The prevalence of preterm births has dropped in recent years, but more than 11 percent of U.S. infants are delivered before 37 weeks of gestation. More than 450,000 babies were born preterm in 2012, one in every nine deliveries.
“Preterm birth is the largest single cause of infant death in this country,” said Rita Driggers, MD, FACOG, associate professor of gynecology and obstetrics at The Johns Hopkins School of Medicine. “It is also the leading cause of neurological defects in infants. Our goal is simple: prevent preterm birth.”
Dr. Driggers discussed the variety of interventions available to deal with preterm birth during a clinical seminar on “Preterm Birth: Cerclage, 17-OH-P, Vaginal Progesterone, Tocolyze, or Cross Your Fingers?” Crossing your fingers is never a good option, she said, but the others have a place in reducing preterm birth.
The mechanisms of preterm birth remain a mystery. Contributing factors include uterine overextension, cervical insufficiency, low maternal weight, nutritional insufficiency, stress, tobacco use, recreational and illicit drug use, allergic disorders, hormonal changes and vascular factors.
Universal cervical ultrasound screening could help identify women at risk for cervical insufficiency, Dr. Driggers said. Johns Hopkins Medicine has a prenatal screening program that begins with abdominal ultrasound.
If the cervix is 35mm or larger, usual prenatal care is appropriate. Women with a small cervix may be candidates for vaginal ultrasound screening, which provides a more accurate measurement. Women with a short cervix may be candidates for vaginal progesterone starting between 16 and 24 weeks.
While ACOG does not support universal screening, the College advises appropriate quality control measures and sonographers credentialed by either the Fetal Medicine Foundation or the Cervical Length Education and Review Program when screening is used.
Other preventative measures include halting elective deliveries prior to 39 weeks, encouraging women to remain on contraception to extend the time between pregnancies, counseling to aid smoking and drug use cessation, nutritional support, and psychosocial support as needed.
No known treatments are effective in preventing preterm birth for twins, Dr. Driggers said. There are a variety of interventions that can reduce preterm births, delay preterm delivery and reduce morbidity and mortality in preterm babies.
Intramuscular progesterone, or 17-alpha hydroxyprogesterone caproate, better known as 17-OH-P or 17P, can help prevent preterm birth in women with a history of preterm births. Physicians don’t use 17P in women who do not have a history of preterm birth or who are carrying more than one fetus.
For women who have no history of preterm birth but are at risk due to a short cervix, vaginal progesterone is the agent of choice. Vaginal progesterone has shown a 45 percent reduction in preterm births in women who are carrying a singleton. It has shown no benefit for women carrying twins in clinical trials.
Cerclage has been shown to reduce preterm birth in women with a short cervix carrying a singleton. “Short” is either less than 15 cm or less than 25 cm, depending on the trial. But cerclage can more than double the risk of preterm birth in women carrying twins.
Small studies suggest that a pessary can also be effective in preventing preterm birth in women with a short cervix. More data are needed, Dr. Driggers said, and more than 20 clinical trials are under way.
Tocolytics can delay preterm labor up to seven days, she said. There are no data showing differences in effectiveness between beta agonists, calcium channel blockers, or NSADS, the three classes of tocolytics approved in the United States.
Magnesium sulfate given during delivery can reduce the risk and severity of cerebral palsy.