Learn what causes premature labor and how to prevent it from happening.

woman in labor in hospital
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If your due date is weeks away, you've probably got lots of time to anticipate Baby’s arrival – but sometimes delivery comes sooner than expected. While health care for preemies is improving, taking steps to prevent preterm labor and its complications is vital. Here’s everything you need to know about the causes of preterm labor, with tips for preventing it from happening.

What is Preterm Labor?

“Preterm labor is when a woman goes into labor too early or is having contractions prior to 37 weeks of pregnancy,” says Colleen Wittenberg, M.D., an Ob-Gyn with Kaiser Permanente in Riverside, CA. “It’s associated with changes in your cervix, namely dilation and/or thinning out of the cervix.” She adds that preterm labor without delivery is a common reason for hospital admissions, but 30-50% of women with preterm labor will not deliver a premature baby.

Jimmy Belotte, interim medical director for the Division of General Ob-Gyn at Montefiore Health System in the Bronx, NY, says that 18% of births worldwide may occur preterm. In the U.S., about 12% of deliveries are premature, and spontaneous preterm labor is responsible for about half of these. Most of the time, preterm labor comes on suddenly and without warning. Symptoms include contraction-like pain, pelvic pressure, and spotting.

Unfortunately, preterm labor can have negative consequences for the mother. “Preterm labor itself could mean a need for the mother to be on bed rest, which can increase her risk of blood clots in her legs. It could also mean the need for her to be exposed to medications in an attempt to slow down the contractions, which carry side effects of their own,” says Kaylah Rondon, a physician at Atlantic Medical Group’s Women’s Health in Westfield, NJ. She says preterm labor is especially dangerous if it results in premature birth; in many cases, the mother has to undergo an emergency cesarean section, which raises her risk for blood loss, infection, and other complications.

If preterm labor results in premature birth, the baby may suffer side effects as well. That’s because premature babies tend to have more health problems than those born full term, requiring a stay in the neonatal intensive care unit. “The earlier the baby is born, the higher the risk for health problems, especially if the baby is not able to breathe on his own or is too small, or considered to have low birth weight (less than 5lbs, 8 oz),” says Dr. Wittenberg. Babies with low birth weight may have trouble eating and gaining weight, and they're susceptible to infections. They also may experience long-term problems with their vision, hearing, and respiratory system, as well as developmental and intellectual disabilities.

Causes of Preterm Labor

The causes of preterm labor aren't yet understood, but the latest research suggests that it may be triggered by the body's natural response to certain bacterial infections such as these:

  • Vaginal infections: Studies suggest that a common infection called bacterial vaginosis (BV) may double a woman's chances of delivering prematurely. BV, which affects 12 to 22 percent of pregnant women, is caused by an overgrowth of bacteria that naturally occur in the vagina. Fortunately, a safe treatment that significantly lowers the rate of preterm delivery is available – talk to your doctor.

  • Infection of the fetal membranes: Studies have shown that any bacterial infection affecting the amniotic fluid and fetal membranes can increase your risk for delivering prematurely. Once diagnosed, however, these infections can be treated with antibiotics that are safe for mother and baby.

  • Periodontal (gum) disease: A small 1996 study from the University of North Carolina School of Dentistry reported that women who had severe periodontal disease faced a sevenfold increase in their risk of preterm delivery. While more studies are needed to confirm this, researchers speculate that the infection may prompt the production of hormone-like substances that trigger labor. Unfortunately, the treatments for periodontal disease aren't recommended for pregnant women. If you have any signs of gum disease – bleeding gums, a receding gumline, or loose teeth – your dentist should be able to advise you on proper dental care during pregnancy.


Risk Factors of Preterm Labor

Up to two-thirds of preterm deliveries affect women with no risk factors, says Dr. Belotte. Even so, here are some risk factors of preterm labor:

  • History of preterm labor:”In a woman with a history of spontaneous preterm labor and delivery, there is up to 30% increased odds that the condition may happen again, usually around the same weeks of pregnancy,” says Dr. Belotte.
  • Premature rupture of membranes
  • Being pregnant with multiples
  • Infection
  • Placenta previa
  • Placental abruption
  • Maternal and fetal stress
  • Uterus problems
  • Smoking and substance abuse during pregnancy
  • Medical conditions like high blood pressure, diabetes, urinary tract infections, or blood clotting problems
  • Maternal age (under 17 or over 35)  

How to Prevent Preterm Labor

To prevent preterm labor, Dr. Belotte recommends progesterone supplementation, which relaxes the uterus and decreases its tendency to initiate contractions. He also suggests “sonographic measurement of the length of the uterine cervix with a diagnosis of a short cervix, and placement of cervical cerclage for those with cervical insufficiency.” Spacing out the pregnancies (by at least 18 months) may also help prevent preterm labor.

Some medications can help manage the side effects of preterm labor, including tocolytics, magnesium sulfate, and corticosteroids. “Tocolytics are drugs that are used to decrease or abort the uterine contractions, therefore allowing time (48 hours) for the administration of corticosteroids,” says Dr. Belotte. “Corticosteroids are a class of medications proven to improve the health outcomes of preterm babies. Specifically, they accelerate fetal lung maturity and decrease the incidence or the severity of fetal brain hemorrhage and fetal bowel complications.”  

Contact your doctor if you think you’re experiencing preterm labor. And remember that while prematurity is common, there are a number of steps you and your doctor can take to prevent it or lessen its complications in your baby. The prognosis for the littlest infants seems to get better all the time.

American Baby