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For the 12th year in a row, Yale-New Haven has been highly ranked by U.S. News & World Report for its programs in gynecology.

Hormone cuts risk of preterm births

This finding represents a major advance in successfully managing women at high risk for delivering their babies prematurely. We have had effective screening tests to identify women who are very likely to deliver early, but we’ve lacked an effective way to treat these women once they’ve been identified.

The problem of preterm birth
Most of our efforts have focused on slowing down labor contractions in women about to deliver prematurely, but this has had little effect on the mortality rates of premature babies. Preterm birth is the leading cause of infant mortality in the U.S., and it’s the leading cause of cerebral palsy, chronic lung disease, blindness and mental retardation.

Preterm birth is the biggest risk pregnant women, particularly African-American women, face even though few women are aware of its threat. The March of Dimes recently surveyed pregnant women, and found that fewer than one percent thought preterm birth was a serious problem.

Progesterone
Progesterone reduced the incidence of preterm birth by more than 30 percent in this study. In addition, progesterone is a very safe, readily available, natural substance with no risks to either the mom or infant. We’re not sure exactly how the progesterone acts to deter preterm birth, but it may interfere with biological mechanisms that come into play in more than one of the causes we’ve identified.

Primary causes of preterm birth
Researchers have identified four primary causes of preterm births: multiple births, vaginal infections, uterine bleeding and stress. The incidence of premature births has increased 27 percent in the last 20 years. The major factor in this increase is the rise in multiple births resulting from assisted reproductive technologies, such as in vitro fertilization. Women pregnant with multiple fetuses tend to deliver early.

Ascending genital tract infections are thought to account for about 40 percent of preterm deliveries.

Uterine bleeding, which occurs when the placenta separates from the uterine wall (i.e., an abruption), also leads to preterm delivery. The bleeding causes the generation of thrombin, a blood-clotting factor that causes an outpouring of enzymes that can break down the fetal membrane, resulting in preterm membrane rupture, a common antecedent to preterm delivery. Thrombin also binds to receptors on uterine muscle cells to trigger contractions.

Cigarette smoking, cocaine use and high blood pressure have all been linked to abruptions, but women with a genetic predisposition to clotting are also at high risk.

Stress can also be a factor. There’s evidence that high levels of anxiety, depression and major life events such as loss of a job, death of a family member and divorce are associated with higher rates of prematurity.

The more striking link, though, is with fetal stress, and there’s lots of evidence that the placentas of many women who deliver prematurely have impaired blood flow, which we know can lead to fetal stress. Smoking, clotting abnormalities and first pregnancies are associated with impaired flow.

Screening tests for those at risk
We have two tests that are effective in predicting which women are likely to deliver early: fetal fibronectin and cervical length.

The presence of fetal fibronectin in vaginal secretions is the most powerful single predictor. This test, done by vaginal swab, along with a vaginal ultrasound to measure cervical length can identify which women might benefit from progesterone treatment. High levels of fetal fibronectin and short cervical length place women at high risk—almost 50 percent—for preterm birth. Low fetal fibronectin and long cervical length indicate a very low risk.

Who should be screened? Women with the following risk factors should talk with their physicians about whether these screening tests are appropriate for them.

• Multiple gestation (twins and more)
• Prior preterm birth
• Mid-pregnancy vaginal bleeding
• Infection
• Cervical incompetence (or weakness)
• Early cervical dilation
• African-American ethnicity
• Low pre-pregnancy weight
• Smoking or illegal drug use

What can women do?
The best preventive strategy is to be in great shape before you become pregnant. Don’t smoke. Maintain a healthy body weight. Women who are overweight have a higher incidence of preclampsia, high blood pressure and diabetes—all of which can result in early deliveries.

Underweight women are also at a higher risk for preterm delivery. Eat a healthy diet and exercise. These factors alone reduce a woman’s risk of preterm birth significantly.

Then, when you do become pregnant, take your prenatal vitamins and folic acid. Maintain a healthy lifestyle and receive regular prenatal care.

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Dr. Lockwood is chief of obstetrics/gynecology at Yale-New Haven Hospital and professor and chair of obstetrics/gynecology at the Yale School of Medicine.