Preterm labor is labor that happens too early, before 37 weeks of pregnancy. If you have preterm labor, your health care provider may recommend some treatments that may help stop your contractions and prevent health problems for you and your baby. They aren’t guaranteed, but research shows that they do help some people.

What kinds of medicines are used in preterm labor?

Antenatal corticosteroids (also called ACS). These include medicines such as betamethasone and dexamethasone. These speed up your baby’s lung development. They also help reduce your baby’s chances of having certain health problems after birth, including respiratory distress syndrome (also called RDS), intraventricular hemorrhage (also called IVH) and necrotizing enterocolitis (also called NEC). RDS is a condition that affects a baby's breathing. IVH is bleeding in the brain. NEC is a condition that affects a baby's intestines.

Antibiotics. These medicines, which include ceftriaxone, clarithromycin, and metronidazole, kill infections caused by bacteria. If you have a positive Group B strep test, or if you have preterm premature rupture of membranes (also called PPROM), your health care provider may give you antibiotics to help prevent infections in you and your baby. PPROM is when the sac around your baby breaks before 37 weeks of pregnancy.

Tocolytics. These medicines may be used to slow or stop labor contractions. There are several types, including:

  • beta-adrenergic receptor agonists,
  • calcium channel blockers,
  • magnesium sulfate, and
  • nonsteroidal anti-inflammatory drugs, or NSAIDs.

Tocolytics may delay labor, often for just a few days. This delay may give you time to get treatment with ACS or to get to a hospital that has a NICU (neonatal intensive care unit). A NICU is a specialized nursery where newborns get medical care. If you have a health condition, such as a heart problem or severe preeclampsia, some tocolytics may not be safe for you. Preeclampsia is a condition that can happen after the 20th week of pregnancy or right after pregnancy. It’s when a pregnant woman has high blood pressure and signs that some of her organs, like her kidneys and liver, may not be working properly. Some of these signs include having protein in the urine, changes in vision and severe headache.

Do medicines used during preterm labor have side effects?

Yes. A side effect is an effect of a drug or medicine that is not the intended result. For example, a side effect of some cold medicines is that they make you sleepy. Side effects can be different for everyone

What side effects can antenatal corticosteroids cause?

Antenatal corticosteroids are given as two injections within a 24 to 48-hour period. Possible side effects for you may include elevated blood sugar. If you take insulin and receive antenatal corticosteroids, your insulin regimen may need to be adjusted.

What side effects can tocolytics cause?

Beta-adrenergic receptor agonists may cause your baby to have a fast heartbeat. Possible side effects for you may include:

  • Chest pain; fast or irregular heartbeat
  • Breathing trouble; fluid in the lungs
  • Diarrhea, nausea (feeling sick to your stomach), throwing up
  • Feeling dizzy; shaking or feeling nervous; seizures
  • Fever, headache
  • High blood sugar
  • Low blood pressure; low blood potassium

Side effects of calcium channel blockers for you may include:

  • Constipation, diarrhea, nausea
  • Feeling dizzy or faint
  • Headache
  • Low blood pressure
  • Redness of the skin

Magnesium sulfate may cause the following side effects for your baby:

  • Being tired and drowsy
  • Slowed breathing
  • Weak muscles
  • Low levels of calcium and bone problems, if the medicine is used for more than 5 to 7 days.

Side effects of magnesium sulfate for you may include:

  • Breathing problems, fluid in the lungs
  • Dry mouth
  • Fatigue (being very tired), weak muscle
  • Headache, double vision, slurred speech
  • Heart attack
  • Nausea or throwing up
  • Redness of the skin, heavy sweating

NSAIDs, such as indomethacin. For your baby, these medicines may cause:

  • Bleeding in the brain or heart
  • Patent ductus arteriosus, also called PDA. This is a heart problem that’s common in premature babies.
  • Jaundice. This is a common condition caused by too much bilirubin in the blood. Jaundice refers to the temporary yellow color of the skin and white parts of the eyes.
  • Kidney problems, such as making too little urine
  • Necrotizing enterocolitis. This is a problem in a baby’s intestines.
  • Rising blood pressure in the lungs

Side effects for you might include:

Talk with your health care provider about the benefits and risks of medicines.

Last reviewed: December 2020