Preterm labor and calcium channel blockers

A typical pregnancy lasts about 40 weeks. When a woman goes into labor at 37 weeks or earlier, it’s called preterm labor and the baby is said to be premature. Some premature babies need special care when they’re born, and some have long-term physical and mental disabilities because they don’t have enough time to develop fully

Calcium channel blockers (CCBs), commonly used to reduce blood pressure, can also be used to relax uterine contractions and postpone a preterm birth. A common CCB for this purpose is nifedipine (Procardia).

Read more: What is preterm labor? »

Symptoms of preterm labor

The symptoms of preterm labor can be obvious or subtle. Some symptoms include:

  • regular or frequent contractions
  • pelvic pressure
  • lower abdominal pressure
  • cramps
  • vaginal spotting
  • vaginal bleeding
  • water breaking
  • vaginal discharge
  • diarrhea

See your doctor if you experience any of these symptoms or feel you may be going into labor early.

Causes and risk factors

Causes of going into labor prematurely are hard to identify.

According to the Mayo Clinic, any woman can go into labor early. Risk factors linked to preterm labor are:

  • having a previous premature birth
  • being pregnant with twins, or other multiples
  • having problems with your uterus, cervix, or placenta
  • having high blood pressure
  • having diabetes
  • having anemia
  • smoking
  • using drugs
  • having genital tract infections
  • being underweight or overweight before pregnancy
  • having too much amniotic fluid, which is called polyhydramnios
  • bleeding from the vagina during pregnancy
  • having an unborn baby who has a birth defect
  • having an interval of fewer than six months since the last pregnancy
  • having little or no prenatal care
  • experiencing stressful life events, such as the death of a loved one

Tests to diagnose preterm labor

Your doctor may perform one or more of these tests to diagnose preterm labor:

  • a pelvic exam to determine if your cervix has begun to open and to determine the tenderness of your uterus and the baby
  • an ultrasound to measure the length of your cervix and determine your baby’s size and position in your uterus
  • uterine monitoring, to measure the duration and spacing of your contractions
  • maturity amniocentesis, to test your amniotic fluid to determine your baby’s lung maturity
  • a vaginal swab to test for infections

How do calcium channel blockers work?

Doctors commonly prescribe CCBs to postpone preterm labor. The uterus is a large muscle made up of thousands of muscle cells. When calcium enters these cells, the muscle contracts and tightens. When calcium flows back out of the cell, the muscle relaxes. CCBs work by preventing calcium from moving into the muscle cells of the uterus, making it less able to contract.

CCBs are a subset of a group of drugs called tocolytics. One study shows that nifedipine is the most effective CCB for postponing preterm labor and that it’s more effective than other tocolytics.

How effective is nifedipine?

Nifedipine can reduce the number and frequency of contractions, but its effect and how long it lasts varies from one woman to another. Like all tocolytic medications, CCBs don’t prevent or delay preterm delivery for a significant period.

According to one study, CCBs can delay delivery for several days, depending on how far a woman’s cervix is dilated when starting medication. This may not seem like a lot of time, but it can make a big difference for the development of your baby if you’re given steroids along with CCBs. After 48 hours, steroids can improve your baby’s lung function and reduce their risk of mortality.

What are the possible side effects of nifedipine?

According to the March of Dimes, nifedipine is effective and relatively safe, which is why doctors use it so much. Nifedipine has no side effects for your baby. The possible side effects for you may include:

  • constipation
  • diarrhea
  • nausea
  • feeling dizzy
  • feeling faint
  • a headache
  • low blood pressure
  • redness of the skin
  • heart palpitations
  • a skin rash

If your blood pressure drops for a prolonged period, it can affect blood flow to your baby.

Are there women who shouldn’t take nifedipine?

Women with medical conditions that could be made worse by the side effects described above should not take CCBs. This includes women with low blood pressure, heart failure, or disorders that affect muscle strength.


Going into preterm labor can affect the development of your baby. CCBs are a safe and effective way to postpone preterm labor. CCBs postpone labor for up to 48 hours. When you use a CCB along with corticosteroids, the two drugs can help the development of your baby before birth and help ensure you have a safe delivery and a healthy baby.