Calculations

1. Overview

   PeriStats is a database-driven website that aggregates data from multiple government agencies and organizations, including:

   • National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC)
   • National Center for Chronic Disease Prevention and Health Promotion, CDC
   • National Center for HIV, STD, and TB Prevention, CDC
   • National Birth Defects Prevention Network (NBDPN)
   • Centers for Medicare and Medicaid Services (CMS), Department of Health and Human Services (DHHS)
   • Health Resources Services Administration (HRSA), DHHS
   • Substance Abuse and Mental Health Services Administration (SAMHSA)
   • U.S. Census Bureau
   • Agency for Healthcare Research and Quality (AHRQ)
   • March of Dimes

   A primary goal of the website is to present health indicators that are comparable across the entire United States, and to show these indicators at the state, county and city level, when possible. The majority of the health indicators on PeriStats are calculated by the March of Dimes Perinatal Data Center using data obtained electronically from the source agency. Those data not calculated directly by the Perinatal Data Center are obtained directly from the source agency or their publications.

2. Perinatal Data Center Calculations

   Calculations performed by the Perinatal Data Center generally follow the guidelines provided by the National Center for Health Statistics (NCHS).

   
   

   Rates

   Rates calculated by the Perinatal Data Center are processed using a series of programs written in SPSS/SAS software. All U.S. total rates are based on the 50 states and the District of Columbia. Some rates are presented as aggregates for a combination of years (e.g. 2017-2020). Due to insufficient numbers, some rates cannot be shown on PeriStats. When rates for single years cannot be shown, three-year aggregates are shown, if available. If the three-year aggregates are not sufficient, that indicator will not be provided in order to ensure confidentiality.

   When an item on a birth or death certificate is illegible or missing, it is coded by NCHS as "not stated" or "unknown." Denominators used in rates and ratios on PeriStats exclude values that are coded as "not stated" or "unknown".

   
   

   Maternal Race/Ethnicity and Age

   Many indicators are shown by race, race/ethnicity, and maternal age. Data provided by race and race/ethnicity reflect the race and ethnicity of the mother as indicated on the birth certificate. Race categories shown on PeriStats include: White, Black, American Indian/Alaska Native, and Asian/Pacific Islander, consistent with those reported by NCHS. Race/ethnicity categories include: non-Hispanic white, non-Hispanic black, non-Hispanic American Indian/Alaska Native, non-Hispanic Asian/Pacific Islander, and Hispanic. Race and ethnicity are reported separately on the birth certificate. When race of the mother is missing from the birth certificate, NCHS assigns race using race of the father, if available, or by assigning the specific race of the mother on the preceding record with a known race of mother (5.9% of live births in 2015).

   While some states report the mother's age directly, most states do not, and maternal age is calculated by NCHS using the difference between the mother's and infant's dates of birth as reported on the birth certificate. From 1964 to 1996, births reported to mothers younger than age 10 or older than age 49 years had age assigned according to the age of mother from the previous record with the same race and total birth order. After 1997, this range changed to mothers reported to be younger than age 9 or older than age 55. For records where age of mother was not reported, maternal age was assigned as previously described (0.01% of live births in 2015).

   
   

   State Departments of Health

   While one strength of PeriStats is the ability to make comparisons between states/local areas or between any state/local area and the U.S., the website is only a starting point for obtaining state and local data. We encourage users to work with their state health departments to analyze data in order to gain a deeper understanding of maternal and infant health issues specific to their area.

   Data provided on PeriStats may differ from rates obtained by state health departments and vital statistics agencies and this could be due to multiple causes. As part of the Vital Statistics Cooperative Program, states are required to send the National Center for Health Statistics (NCHS) natality and mortality data for a given year by a specific date. Sometimes states receive data after this date, which may result in slight differences in the rates calculated using NCHS processed data and state-processed data. Another reason rates may differ could be differences in the way NCHS and the states calculate variables and input missing data.

3. Binge Alcohol Use

   Binge alcohol use among women of childbearing age is derived from the Behavioral Risk Factor Surveillance Survey (BRFSS), which is a health survey conducted by 50 states, 3 territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Alcohol use is part of a rotating core of questions asked every other year.

   The calculation for the BRFSS binge drinking indicator is performed by the March of Dimes Perinatal Data Center, and includes the percent of women of childbearing age (18-44 years) who engage in binge alcohol use. Binge alcohol use is defined as having four or more drinks on at least one occasion during the past month. The U.S. rate is the median value for all states which provided data during the year. More background can be found at the BRFSS website.

4. Birth Defects Prevalence

   The National Birth Defects Prevention Network (NBDPN) and the Centers for Disease Control and Prevention support state-specific birth defect surveillance programs that collect data on major birth defects (i.e., conditions present at birth that cause adverse structural changes in one or more parts of the body). The NBDPN produces an annual Congenital Malformations Surveillance Report that includes state-level data on major birth defects and a directory of population-based birth defects surveillance systems in the United States.

   Data from the report are displayed on PeriStats and include the prevalence rates of birth defects by maternal race/ethnicity. Gastroschisis and chromosomal defects are also stratified by maternal age at delivery. The full report can be found on the NBDPN website. Updated data may be available on state-specific websites.

   NBDPN reports the prevalence of each birth defect as the total birth defect cases for any pregnancy outcome for 'X' years, divided by the total live births for those years. The calculated number is then multiplied by 10,000. The total live birth denominator is used for all reported birth defects except for hypospadias, which is calculated using a denominator of total male live births, and turner syndrome which is calculated using a denominator of total female live births.

   State programs have different rules for cell suppression to protect confidentiality. Refer to the footnotes beneath each graph or table for more information on state-specific cell suppression.

   State birth defects surveillance programs report race/ethnicity using the categories required by the NBDPN, which are compatible with the federal standards. These categories may differ from categories used in other reports published by state health departments and may differ from the way race/ethnicity is reported from other sources of data shown in PeriStats. For more information, refer to the NBDPN Guidelines for Conducting Birth Defects Surveillance.

   Differences in state surveillance program methodology exist and may change over time. For example, state surveillance programs vary in the number and type of data sources used to seek out cases and the diagnostic coding systems used to classify birth defects. State programs also vary in the inclusion of different pregnancy outcomes in the case definition. For a detailed description of state-specific methods, refer to the directories located in the Congenital Malformations Surveillance Report. Contact the specific state program for more details about their surveillance methodology.

5. Fertility Rates and Percentage of Births

   Fertility rates are the number of live births per 1,000 persons in a specified group. Fertility rates on PeriStats are calculated as the number of live births per 1,000 women, 15-44 years of age. The denominator for this calculation is based on population data from the U.S. Census Bureau, available through the National Center for Health Statistics website. For more information, see calculation notes on Population.

   Percentage of births calculations show the distribution of live births by race, race/ethnicity, and maternal age. Calculations are based on the number of live births in a specified group, divided by all live births, multiplied by 100. Data for distributions by race and maternal age sum to 100 percent. Distributions by race/ethnicity do not sum to 100% due to live births missing data on ethnicity.

6. Birthweight
   Birthweight rates are stratified into three categories: very low birthweight (less than 1500 grams or 3 1/3 pounds), low birthweight (less than 2500 grams or 5 1/2 pounds, includes very low birthweight). Calculations are based on the number of live births to infants in a specific birthweight category divided by all live births, minus the missing values and then multiplied by 100. Low birthweight and very low birthweight rates among singletons and multiples are calculated the same way.
7. Delivery Method

   Note: In 2003 states started to implement the 2003 revision of the U.S. Standard Certificate of Live Birth and by 2016 all states had completed implementation. Some method of delivery data is not comparable across revisions. As of June 2018, select delivery method indicators based on the 1989 revision of the birth certificate are no longer available on PeriStats. A limited number of delivery method indicators and years are available on PeriStats for states that implemented the 2003 revision most recently. See detailed description below.

   
   

   Calculation

   Delivery method rates are calculated for total Cesarean births, primary Cesarean births, vaginal births after Cesarean births (VBAC), and repeat Cesarean births.

   The total Cesarean birth rate is calculated as the number of births delivered by Cesarean divided by the total number of live births minus the not-stated values for delivery method, multiplied by 100.

   The primary Cesarean birth rate is calculated as the number of women having a first Cesarean delivery divided by the number of live births to women who have never had a Cesarean delivery, multiplied by 100. The denominator for this rate excludes those with method of delivery classified as repeat Cesarean, vaginal birth after previous Cesarean, or if the method was not stated.

   The VBAC rate is calculated as the number of VBAC deliveries resulting in a live birth divided by the sum of VBAC and repeat Cesarean deliveries, multiplied by 100.

   The repeat Cesarean birth rate is calculated as the number of repeat Cesarean deliveries resulting in a live birth divided by the sum of VBAC and repeat Cesarean deliveries, multiplied by 100.

   
   

   Impact of Birth Certificate Revision

   The transition from the 1989 revision of the U.S. Standard Certificate of Live Birth to the 2003 revision has some implications on tracking rates of primary and repeat Cesarean births and VBAC deliveries in the United States. ⁽¹⁾ The method of delivery item on the 2003 revision specifically asks if the mother had a previous Cesarean birth under the "Risk Factors for Pregnancy" section of the birth certificate. In past revisions this information was indicated by a checkbox for VBAC under the method of delivery section. As a result of this modification, rates of VBAC and primary Cesarean birth from the 2003 revision are not comparable to data collected using earlier birth certificate revisions. Specifically, under the 2003 revision, rates of VBAC deliveries and primary Cesarean births are slightly higher than expected, and repeat Cesarean births are slightly lower. Total Cesarean section and vaginal delivery rates are not impacted.

   The state implementation of the 2003 revision also impacts U.S. and state temporal trends. While some states began using the revised birth certificate in 2003, the schedule for implementation varies by state. Therefore, starting in 2003, total U.S. rates of VBAC and primary Cesarean deliveries are not reported due to data incompatibilities between states. Furthermore, some states have implemented the 2003 revision mid-year, and in these cases data for that year are not shown. New Jersey's implementation spanned two years (2014-2015) and therefore data on primary, repeat, and VBAC deliveries is available on PeriStats beginning with 2016 data.

   Beginning in June 2018, data on delivery method based on the 1989 revision of the birth certificate is no longer displayed on PeriStats. All states implemented the 2003 birth certificate by 2016. In addition, the functionality that allows you to make comparisons between regions will show only the years for which both areas have data available. States implemented the 2003 revision of the birth certificate in the following years:

   • 2003: PA, WA
   • 2004: FL (mid-year), ID, KY, NH (mid-year), NY (excluding New York City), SC, TN
   • 2005: KS, NE, PR, TX, VT (mid-year)
   • 2006: CA (partially), DE, ND, OH, SD, WY
   • 2007: CO, GA (mid-year), IN, IA, MI (partially)
   • 2008: MT, NM, New York City, OR
   • 2009: DC (mid-year), NV (mid-year), OK (mid-year), PR, UT
   • 2010: IL, LA (mid-year), MD, MO, NC (mid-year)
   • 2011: MA (mid-year), MN (mid-year), WI
   • 2012: VA (mid-year)
   • 2013: AK, ME (mid-year), MS
   • 2014: AL, AZ, AR, HI, NJ (mid-year), WV
   • 2015: NJ (mid-year)
   • 2016: CT

   1. Martin JA, Hamilton BE, Sutton PD, et al. Births: Final data for 2003. National vital statistics reports; vol 54 no 2. Hyattsville, MD: National Center for Health Statistics. 2005.

   Low-risk Celsarean birth rates were calculated as: the number of Cesarean births that occurred to first-time mothers of a single infant, positioned headfirst with a agestational age of at least 37 weeks, divided by the number of first -time mothers of a single infant, positioned headfirst with a gestational age of at least 37 weeks, multiplied by 1,000. This is often referred to as the NTSV Cesarean birth rate. NTSV is an abbreviation for nulliparous, term, singleton and vertex.

8. Federal Poverty Level
   The percent of women (15-44 years) and children (<20 years) below the federal poverty level is obtained from the U.S. Census Bureau. Data is collected by the Census using the Current Population Survey (CPS), a monthly survey of about 50,000 households. The sample is selected to represent the civilian, non-institutional population. More background can be found at the CPS website.
9. Fetal and Perinatal Mortality Rates

   Fetal death is defined as death that occurs prior to the delivery of a fetus, and which is not an induced termination of pregnancy. In PeriStats, data are presented for "late fetal deaths" and include those with a stated period of gestation that is 28 weeks or more. Late fetal mortality rates are computed as: the number of fetal deaths at 28 weeks of gestation or more, divided by the number of live births and fetal deaths at 28 weeks or more, multiplied by 1,000.

   Perinatal death refers to a death that occurs around the time of delivery. In PeriStats, perinatal mortality includes infant deaths less than seven days of age and late fetal deaths at 28 weeks of gestation or more. Perinatal mortality rates are calculated as the number of infant and fetal deaths, divided by the number of live births and fetal deaths.

   The population at risk for fetal and perinatal death is represented in the denominator of the calculation as: the number of live births plus fetal deaths, in a specified age group. For late fetal mortality rates, the numerator is calculated using data from the Fetal Death Data File from NCHS. The denominator is calculated using data from the Final Natality File from NCHS for the number of live births and the Fetal Death Data File for the number of fetal deaths at 28 weeks gestation or more. For perinatal mortality rates, the numerator is calculated using data from Fetal Death Data File from NCHS and numerator file in Period Linked Birth/Infant Death Data Set. The denominator is calculated using the Fetal Death Data file from NCHS and the Live Birth Denominator File in Period Linked Birth/Infant Death Data Set that accompanies the numerator file.

   Reporting requirement for fetal death data

   Reporting requirements for fetal deaths vary by state and these differences have important implications for comparisons of fetal and perinatal mortality rates by state. ⁽¹⁾ The majority of states require reporting of fetal deaths of 20 weeks of gestation or more, or a minimum of 350 grams birthweight or some combination of the two. More information about state reporting requirements can be found in the Fetal and Perinatal Mortality, United States report (National Vital Statistic Reports, NCHS). PeriStats presents late fetal mortality rates in order to account for these differences and provide more comparable data across states.

10. Illicit Drug Use

    Illicit drug use among population ages 12 and older is derived from the National Survey on Drug Use & Health (NSDUH), which is the primary source of statistical information on the use of illegal drugs by the U.S. population. The survey is sponsored by the Substance Abuse and Mental Health Services Administration (SAMHSA). The NSDUH collects information from residents of households, non-institutional group quarters (e.g., shelters, rooming houses, dormitories), and civilians living on military bases. Persons excluded from the survey include homeless persons who do not use shelters, active military personnel, and residents of institutional group quarters, such as jails and hospitals.

    A small subset of data from NSDUH is available on PeriStats, and includes the percent of the population ages 12 and older that engage in illicit drug use. To ensure reliability, data are provided for a two-year combined period. Illicit drug use indicates past month use at least once of marijuana/hashish, cocaine (including crack), inhalants, hallucinogens (including PCP and LSD), heroin, or any prescription-type psychotherapeutic used non-medically. More background is available at the NSDUH website.

11. Infant Mortality

    Infant Mortality Rates

    Infant mortality rates are calculated as; the number of deaths in the first year of life, divided by the number of live births, multiplied by 1000. The numerator is calculated using data from the Period Linked Birth/Infant Death File, and the denominator is calculated using the Live Birth Denominator File that accompanies the numerator file.

    Age at Infant Death

    Age at infant death rates include calculations for two age-specific categories: neonatal deaths and postneonatal deaths. The neonatal death rate is calculated as the number of infant deaths that occur between 0-27 days of life (often referred to as the 1st month of life), divided by the number of live births, multiplied by 1,000. The postneonatal death rate is calculated as the number of infant deaths that occur from 28 days to under one year of life, divided by the number of live births, multiplied by 1,000.

    Cause of Infant Death

    Cause of Infant Death rates are calculated using the Period Linked Birth/Infant Death File for the following causes of death: birth defects, preterm birth/low birthweight, sudden infant death syndrome, respiratory distress syndrome, maternal complications of pregnancy, and neural tube defects. Rates are calculated as the number of cause-specific infant deaths, divided by the number of live births, multiplied by 100,000.

    All causes of death are based solely on the underlying cause of death and compiled in accordance with the International Statistical Classifications of Diseases and Related Health Problems - Ninth Revision (ICD-9) for 1995 through 1998, and Tenth Revision (ICD-10) beginning in 1999. When comparing data between these time periods, it is important to consider the potential impact on coding and definitions of cause of death categories that may have occurred upon transitioning from ICD-9 to ICD-10. To compensate for these discontinuities, NCHS has published cause-specific comparability ratios that when applied more clearly represent trends in mortality statistics from 1998 to 1999. Comparability ratios have not been applied in PeriStats.

    
    

    Cause of Death	ICD-9 Codes	ICD-10 Codes
    Birth Defects	P07	765
    Prematurity/LBW	Q00-Q99	740-759
    Sudden infant death syndrome	R95	798.0
    Respiratory distress syndrome	P22	769
    Maternal complications of pregnancy	P01	761

    
    
    

    Deaths due to neural tube defects include anencephalus, craniorachischisis, iniencephaly, spina bifida with and without hydrocephalus and encephalocele.
12. Maternal Mortality

    Maternal death is defined as one that occurs during pregnancy or within 42 days of the end of a pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by a woman's pregnancy, but not from accidental or incidental cause. Maternal mortality rates are calculated as the number of maternal deaths in a calendar year, divided by the number of live births for the same period, multiplied by 100,000. The number of live births used in the denominator is an approximation of the population of pregnant women who are at risk of a maternal death. The numerator is calculated using data from the Final Mortality File from NCHS, included in these deaths assigned an underlying cause of death ICD-10 code of A34, O00-O95, or O98-O99. The denominator is calculated using data from the Natality File from NCHS.

    An update to the maternal mortality calculation method in 2018 introduces two new practices. The first change attempts to reduce reporting errors that lead to over-representation of maternal deaths among older women and the second update makes changes to the coding practices for maternal deaths.

    From 2003-2017 a checkbox was added to the death certificate to indicate whether the decedent was pregnant at the time of death or up to a year before the death occurred. This was previously used for deaths of a person aged 10-54 years of age. The checkbox still remains, however, the 2018 change reflects a practice to reduce the use of the checkbox to only those aged 10-44.

    The second change states that if the checkbox is the only indication of a pregnancy for decedents aged 10-44, a maternal code will be assigned as the underlying cause, except in cases where the underlying cause is an external or incidental cause. This change allows more information from the death certificate to be retained in the underlying cause of death reporting.

    These changes will be reflected in all maternal mortality data starting with the 2018 reporting year and will be incorporated going forward.

    Citations:

    1. Hoyert DL, Heron MP, Murphy SL, Kung H. Deaths: Final Data for 2003. National vital statistics reports; vol 54 no 13. Hyattsville, MD: National Center for Health Statistics. 2006.

    2. Hoyert DL, Minino AM. Maternal Mortality in the United States: Changes in Coding, Publication, and Data Release, 2018. National Vital Statistic Reports; vol 69 no 2. Hyattsville, MD: National Center for Health Statistics. 2020.

13. Maternal Weight

    Maternal weight and body mass index (BMI) are derived from the Behavioral Risk Factor Surveillance Survey (BRFSS) and the Pregnancy Risk Assessment Monitoring System (PRAMS).

    The BRFSS is a health survey conducted by 50 states, three territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Obesity is part of a standard core of questions asked every year.

    Methodological changes to the BRFSS in 2011 have affected the trends in prevalence estimates and they are not comparable to earlier years. The changes include the addition of cellular phones and improvements in the statistical weighting methods.

    The PRAMS survey, from the Centers for Disease Control and Prevention (CDC) in partnership with state health departments, collects state-specific, population-based data to monitor maternal and child health indicators. Each state randomly samples women who have recently had a live birth by selecting from the participating state's birth certificate records. More info for both BRFSS and PRAMS can be found on the CDC website.

    Calculations for Maternal Weight indicators are performed by the March of Dimes Perinatal Data Center, and include the percent of women of childbearing age (18-44 years) defined as obese by BRFSS and BMI category prior to pregnancy from PRAMS. Body Mass Index (BMI) is a number calculated from a person's weight in kilograms divided by the square of height in meters. Obesity is defined as persons who have a Body Mass Index of 30 or more. U.S. rate is the median of states which reported that year. Calculations for PRAMS pre-pregnancy measures reflect standard BMI categories where: a BMI less than 18.5 is underweight, a BMI equal to or above 18.5 and less than 25 is normal weight, a BMI equal to or above 25 and less than 30 is overweight, and a BMI equal to or above 30 is obese.

14. Pregnancy Risk Assessment Monitoring System (PRAMS)

    The Pregnancy Risk Assessment Monitoring System (PRAMS) from the Centers for Disease Control and Prevention (CDC) in partnership with state health departments, collects state-specific, population-based data to monitor maternal and child health indicators. Each state randomly samples women who have recently had a live birth by selecting from the participating state's birth certificate records.

    Data are weighted in order to provide representative estimates of a state’s population. Because the data are based on a weighted sample, PeriStats also displays 95% confidence intervals to assist with interpretation of rates and comparisons.

    Select PRAMS data are available on PeriStats and fall under the following broad categories: Prenatal Care, Smoking and Alcohol Use, Health Insurance and Income, Maternal Weight, Flu Shot, NICU Admissions, Breastfeeding, Infant Safe Sleep, Preconception/Interconception Care, Depression, Intimate Partner Violence and Folic Acid Use. Most data are available stratified by maternal race/ethnicity, age and Medicaid status.

    The availability of PRAMS data varies by state and year. Some topics are not available for certain states and years because of variations in the PRAMS survey and completeness of data across states and over time. A list of data availability by state and year can be found on the PRAMS website.

    PRAMS data for New York City and New York state are reported separately.

    For more on PRAMS methods and questionnaires, visit the PRAMS website.

15. Population
    Population data are shown for three major categories: total population, population of women 15-44 years of age, and total population of children less than 20 years. The data provided are from the following Census estimates; 1996 to 1999 are based on the 1990 Census, 2000 to 2009 are based on the 2000, and years 2010 and later are based on the 2010 Census. Distribution by race and race/ethnicity is also provided for total population, women 15-44 years and children less than 20 years, and by age for women 15-44 years. Beginning with the 2000 Census, race and ethnicity were reported according to standards published by the Office of Budget and Management, which were inconsistent with the reporting of race on vital records, including the birth certificate. In order to adjust for this, the Census Bureau released special population estimates that bridged the gap between these two sources of data. More information on this procedure and the data files can be found at the NCHS website.
16. Prenatal Care

    Note: In 2003 states started to implement the 2003 revision of the U.S. Standard Certificate of Live Birth and by 2016 all states had completed implementation. This significantly impacts the ability to compare temporal and regional prenatal care data. As of June 2018, prenatal care data based on the 1989 revision of the birth certificate is no longer available on PeriStats. Only limited data on prenatal cares is available on PeriStats for states that implemented the 2003 revision most recently.

    Timing of Prenatal Care

    Timing of prenatal care calculations are broken into three categories. These categories include: "Early prenatal care," which is care started in the 1st trimester (1-3 months); "Second trimester care" (4-6 months); and "Late/no prenatal care," which is care started in the 3rd trimester (7-9 months) or no care received. Calculations are based on the number of live births to mothers in a specific prenatal care category, divided by all live births excluding those missing data on prenatal care, multiplied by 100.

    Adequacy of Prenatal Care

    Adequacy of prenatal care calculations are based on the Adequacy of Prenatal Care Utilization Index (APNCU), which measures the utilization of prenatal care on two dimensions. The first dimension, adequacy of initiation of prenatal care, measures the timing of initiation using the month prenatal care began as reported on the birth certificate. The second dimension, adequacy of received services, is measured by taking the ratio of the actual number of visits reported on the birth certificate to the expected number of visits. The expected number of visits is based on the American College of Obstetrics and Gynecology prenatal care visitations standards for uncomplicated pregnancies ⁽¹⁾ and is adjusted for the gestational age at initiation of care and for the gestational age at delivery. The two dimensions are combined into a single summary index, and grouped into four categories: Adequate Plus, Adequate, Intermediate, and Inadequate. On PeriStats, the percent of infants whose mothers received Adequate and Adequate Plus prenatal care are combined into one category, Adequate/Adeq+ prenatal care. Definitions for these categories include:

    • Adequate Plus: Prenatal care begun by the 4th month of pregnancy and 110% or more of recommended visits received.
    • Adequate: Prenatal care begun by the 4th month of pregnancy and 80-109% of recommended visits received.
    • Intermediate: Prenatal care begun by the 4th month of pregnancy and 50-79% of recommended visits received.
    • Inadequate: Prenatal care begun after the 4th month of pregnancy or less than 50% of recommended visits received.
    • Adequate/Adeq+ used on the PeriStats website can be defined as prenatal care begun by the 4th month of pregnancy and 80% or more of recommended visits received.

    
    

    A more detailed description of APNCU can be found in the second resource listed in this section².

    
    

    Impact of Birth Certificate Revision

    The transition from the 1989 revision of the U.S. Standard Certificate of Live Birth to the 2003 revision has multiple implications for tracking rates of prenatal care in the United States.⁽³⁾ First, the timing of prenatal care item has changed. For data collected using the 1989 revision (all data prior to 2003), the item was recorded as the month of pregnancy that prenatal care began as reported by the mother. In 2003 the item was changed to request the date (day/month/year) of the first prenatal care visit, as recorded in the prenatal care or medical record. As a result of these modifications, rates of prenatal care timing and adequacy from the 2003 revision are not comparable to data collected using earlier birth certificate revisions.

    The state implementation of the 2003 revision also impacts U.S. and state temporal trends. While some states began using the revised birth certificate in 2003, the schedule for implementation varies by state. Therefore, starting in 2003, total U.S. rates of timing and adequacy of prenatal care are not reported due to data incompatibilities between states. Comparison of prenatal care between states on different implementation schedules will not be possible. Furthermore, some states have implemented the 2003 revision mid-year, and in these cases data for that year are not shown. In 2006 California did not adopt the 2003 revision of prenatal care items. California fully implemented the 2003 revision in 2007. In 2007 not all births in Michigan are reported based on the 2003 revision, and data are not shown for that year. Finally, New York State implemented the 2003 revision in 2004 and New York City implemented in 2008. Rates of prenatal care for New York state exclude New York City from 2004 to 2007. Data for New York City can be found separately under city/county data. New Jersey's implementation spanned two years, 2014-2015, and therefore data on prenatal care will be available on PeriStats beginning with 2016 data. All states implemented the 2003 birth certificate revision by 2016.

    Beginning in June 2018, data on prenatal care based on the 1989 revision of the birth certificate is no longer displayed on PeriStats. In addition, the functionality that allows you to make comparisons between regions will show only the years for which both areas have data available. States implemented the 2003 revision of the birth certificate in the following years:

    • 2003: PA, WA
    • 2004: FL (mid-year), ID, KY, NH (mid-year), NY (excluding New York City), SC, TN
    • 2005: KS, NE, PR, TX, VT (mid-year)
    • 2006: CA (partially), DE, ND, OH, SD, WY
    • 2007: CO, GA (mid-year), IA, IN, MI (partially)
    • 2008: MT, NM, New York City, OR
    • 2009: DC (mid-year), NV (mid-year), OK (mid-year), PR, UT
    • 2010: IL, LA (mid-year), MD, MO, NC (mid-year)
    • 2011: MA (mid-year), MN (mid-year), WI
    • 2012: VA (mid-year)
    • 2013: AK, ME (mid-year), MS
    • 2014: AL, AZ, AR, HI, NJ (mid-year), WV
    • 2015: NJ (mid-year)
    • 2016: CT

    1. Standards for Obstetric-Gynecologic Services. 6th ed. Washington, DC: American College of Obstetricians and Gynecologists; 1985.
    2. Kotelchuck M. An evaluation of the Kessner Adequacy of Prenatal Care Index and a proposed Adequacy of Prenatal Care Utilization Index. Am J Public Health 1994; 84: 1414-1420.
    3. Martin JA, Hamilton BE, Sutton PD, et al. Births: Final data for 2003. National vital statistics reports; vol 54 no 2. Hyattsville, MD: National Center for Health Statistics. 2005.

17. Preterm Birth

    A preterm birth is defined as a live birth occurring before 37 completed weeks of gestation. Preterm birth rate calculations are based on the number of live births to infants in a specificy gestational age category, divided by all live births, excluding those missing data on gestational age, multiplied by 100. Gestational age is reported as the number of completed weeks of gestation on individual birth certificates and then categorized by NCHS. Preterm birth rate calculations are based on the number of live births to infants in a specific gestational age category divided by all live births excluding those missing data on gestational age, multiplied by 100. Overall, singleton-, and multiple-specific rates are calculated in the same way.

    Beginning with 2014 data, the primary measure used by NCHS to determine the gestational age of the newborn is the obstetric estimate of gestation (OE). This measure replaces the previous measure that was based on the interval between the date of the mother's last menstrual period (LMP) and the infant's date of birth. The OE has been shown to more accurately reflect the true gestational age of the infant than LMP. NCHS edits OE data to include only gestational ages between 17 and 47 completed weeks. In 2014, 0.1% of records were either outside of this range or were missing information.

    Calculations using OE gestational age differ from calculations using LMP gestational age. For example, in 2014, the U.S. preterm birth rate based on OE was 9.6% of live births compared to 11.3% based on LMP. Despite these differences, both measures indicate a decline in the U.S. preterm birth rate between 2007 and 2014.

    In additional to overall preterm births, three subcategories of preterm birth are displayed on PeriStats: very preterm (less than 32 completed weeks); moderately preterm (32-36 completed weeks); and late preterm (34-36 completed weeks).

    As with other indicators, preterm birth rates on PeriStats may differ from those provided directly by state health departments. This may be due to differences in the way the health department and NCHS calculate the gestational age of the infant or in the handling of missing data.

    Additional information on the transition to OE gestational age and differences between OE and LMP gestational age measure can be found in:

    Martin JA, Osterman MJK, Kirmeyer SE, Gregory ECW. Measuring gestational age in vital statistics data: Transitioning to the obstetric estimate. National vital statistics reports; vol 64 no 5. Hyattsville, MD: National Center for Health Statistics. 2015.

    Hamilton BE, Martin JA, Osterman MJK, et al. Births: Final data for 2014. National vital statistics reports; vol 64 no 12. Hyattsville, MD: National Center for Health Statistics. 2015.

    Martin JA, Wilson EC, Osterman MJ, Saadi EW, Sutton SR, Hamilton BE. Assessing the quality of medical and health data from the 2003 birth certificate revision: results from two states. National Vital Statistics Report. 2013 Jul 22;62(2):1-19.

    Dietz PM, Bombard JM, Hutchings YL, Gauthier JP, Gambatese MA, Ko JY, Martin JA, Callaghan WM. Validation of obstetric estimate of gestational age on U.S. birth certificates. American Journal of Obstetrics &Gynecology. 2014 Apr;210(4):335.e1-5. doi: 10.1016/j.ajog.2013.10.875.

    Ambrose CS, Caspard H, Rizzo C, Stepka EC, Keenan G. Standard methods based on last menstrual period dates misclassify and overestimate U.S. preterm births. Journal of Perinatalogy. 2015 April 2:35:411-414.

18. Sexually Transmitted Disease
    Sexually transmitted disease (STD) statistics on PeriStats were obtained from Division of STD Prevention (DSTD), National Center for HIV, STD, and TB Prevention (NCHSTP), Centers for Disease Control and Prevention (CDC). They acquire this data from STD control programs and health departments in the 50 States, the District of Columbia, selected cities, counties, U.S. dependencies and possessions, and independent nations in free association with the United States. Rates for chlamydia, gonorrhea, and syphilis are reported as rates per 100,000 women. Congenital syphilis is reported as a rate per 100,000 live births. Rates for syphilis and congenital syphilis are 5-year averages. More background can be found at the DSTD website.
19. Singleton and Multiple Birth Rates
    Singleton and multiple birth rates are shown for all births, by maternal race, maternal race/ethnicity and maternal age. Multiple birth deliveries are further stratified by twin deliveries and triplet and higher order deliveries. The singleton delivery rate is calculated as the number of singleton live births, divided by all live births, multiplied by 100. All multiple birth calculations are shown as a ratio rather than a percent, and are multiplied by 1000 instead of by 100, consistent with NCHS procedures. This is a ratio, as opposed to a rate, because sets of multiples cannot be determined from the data. Therefore, counts in the numerator represent individual live births that occur from multiple deliveries. Low birthweight, very low birthweight, preterm and very preterm birth rates among singletons and multiples are also shown (see calculation notes on Birthweight and Preterm birth for more information).
20. Smoking

    Smoking among women and men is derived from the Behavioral Risk Factor Surveillance Survey (BRFSS). The BRFSS is a health survey conducted by 50 states, 3 territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Cigarette use is part of a standard core of questions asked every year.

    Methodological changes to the BRFSS in 2011 have affected the trends in prevalence estimates and they are not comparable to earlier years. The changes include the addition of cellular phones and improvements in the statistical weighting methods.

    Calculations for BRFSS smoking indicators are performed by the March of Dimes Perinatal Data Center, and include the percent of women of childbearing age (18-44 years) and of men 18 years and older defined by BRFSS to be smokers. Smokers are defined as persons who have ever smoked 100 cigarettes and currently smoke every day or some days. U.S. rate is the median of states which reported that year. This does not include the use of e-cigarettes. More background can be found on the BRFSS website.

21. Title V
    Title V funding figures are obtained from the Maternal and Child Health Bureau (MCHB), a department of the Health Resources and Services Administration (HRSA), U.S. Department of Health and Human Services (HHS). Title V of the Social Security Act has authorized the Maternal and Child Health Services Program since 1935 and is a major source of state funds for women of childbearing age, infants, children, adolescents and children with special health care needs. Title V consists of block grants to state health agencies on the basis of specified formulas, and discretionary grants referred to as Special Projects of Regional and National Significance. States and jurisdictions must match every four dollars of federal Title V money they receive, by at least three dollars. PeriStats makes available the amount of federal dollars allocated to each state as well as the amount matched by each state and Washington, DC. U.S. totals shown in PeriStats include funding to all 50 states and the District of Columbia, but exclude funding to territories. More background is available on the MCHB website.
22. Uninsured Women and Children
    The percent of uninsured women (15-44 years of age) and children (<19 years) is obtained from IPUMS-USA, University of Minnesota, www.ipums.org using data from the American Community Survey (ACS) from the U.S. Census Bureau. The ACS is a nationwide survey that collects information on demographic, social, economic, and housing characteristics about the U.S. population every year. The ACS is an ongoing survey of about 295,000 households each month, or 3.5 million households annually. PeriStats presents the percent of women and children who do not have any health insurance coverage. A respondent was considered uninsured if they were not covered by any type of health insurance at the time of the survey. Additionally, they were considered uninsured if they only had coverage through the Indian Health Service (IHS). More background can be found at IPUMS-USA or the U.S. Census Bureau websites.
23. Women, Infants and Children (WIC) Program
    The Special Supplemental Nutrition Program for Women, Infants and Children (WIC), is a federally funded program administered by the U.S. Department of Agriculture (USDA), state health departments, city and county health departments and community health clinics. The program serves low-income women, infants and children who are nutritionally at risk. A state may receive additional funds mid-year. PeriStats makes available the number of women and children served by WIC for each state and Washington, DC. Data shown in PeriStats includes participants served by state health departments and excludes those receiving services from the Inter-Tribal Organizations. More background on WIC can be found at the USDA website.
24. Maternity Care Desert Variable

    A maternity care desert is any county in the United States without a hospital or birth center offering obstetric care and without any obstetric providers. Obstetric providers include obstetricians, family physicians who provide obstetric care, certified nurse midwives and certified midwives (CNM/CM). Low access to appropriate preventive, prenatal and postpartum care is defined as counties with one or fewer hospitals or birth centers that provide obstetric care, few obstetric providers (fewer than 60 per 10,000 births) or a high proportion of women without health insurance (10 percent or more). Moderate access to care is defined as living in a county with access to one or fewer hospitals or birth centers and less than 60 obstetric providers and with less than 10% of reproductive-aged women uninsured. Full access to maternity care can be defined as two or more hospitals or birth centers providing obstetric care and 60 or more obstetric providers at the county level.

25. NTSV Calculation

    A low-risk Cesarean birth occurs when a woman undergoes a Cesarean section procedure when the baby is a single infant, is positioned head-first and the mother is full-term (at least 37 weeks), and has not given birth prior.¹ This is also referred to as a NTSV Cesarean birth. NTSV is abbreviated to mean nulliparous (first-time mother), term, singleton, vertex (head first position). Low-risk Cesarean birth rates were calculated using the National Center for Health Statistics 2018 final natality data.² Low-risk Cesarean birth rates were calculated as the number of Cesarean births that occurred to first-time mothers of a single infant, positioned headfirst with a gestational age of at least 37 weeks (NTSV), divided by the number of first-time mothers of a single infant, positioned headfirst with a gestational age of at least 37 weeks (NTSV), multiplied by 1,000.

    1. Martin JA, Hamilton BE, Osterman MJK, Driscoll AK. Births: Final Data for 2018. Natl Vital Stat Rep 2019;68(13):1- Retrieved from: https://www.cdc.gov/nchs/data/nvsr/nvsr68/nvsr68_13-508.pdf

    2. National Center for Health Statistics, final natality data.

26. Folic Acid

    Folic acid use among women is derived from the Pregnancy Risk Assessment and Monitoring System (PRAMS), from the Centers for Disease Control and Prevention (CDC), in partnership with state health departments, collects state-specific, population-based data to monitor maternal and child health indicators. Each state randomly samples women who have recently had a live birth by selecting from the participating state's birth certificate records. Calculations for the PRAMS folic acid use indicator are performed by the March of Dimes Perinatal Data Center. Use is grouped by frequent and infrequent multivitamin use, prenatal vitamin, or folic acid vitamin use among mothers in the month prior to conception. Frequent use is defined as reporting vitamin use four to seven times a week and infrequent use is defined as reporting vitamin use zero to three times a week.

    Weighted rates and 95% confidence intervals are provided for frequent and infrequent vitamin use. For more on PRAMS methods and questionnaires, visit the PRAMS website.

27. Safe Sleep

    Safe sleep is derived from the Pregnancy Risk Assessment and Monitoring System (PRAMS), from the Centers for Disease Control and Prevention (CDC), in partnership with state health departments, collects state-specific, population-based data to monitor maternal and child health indicators. Each state randomly samples women who have recently had a live birth by selecting from the participating state's birth certificate records. Calculations for the PRAMS safe sleep indicator is performed by the March of Dimes Perinatal Data Center. Safe sleep is presented as a combination of reported practices that a caregiver can take to reduce the risk of Sudden Infant Death Syndrome (SIDS). A PRAMS questionnaire respondent is included in the safe sleep category if in the last two weeks they reported:

    • Baby most often laid on back to sleep
    • Baby always slept alone in their own crib or bed
    • Baby slept in the same room as a caregiver
    • Baby usually slept in the absence of blankets, toys, cushions, pillows, and crib bumpers.

    Weighted rates and 95% confidence intervals are provided for safe sleep. For more on PRAMS methods and questionnaires, visit the PRAMS website.