When Karen Dressler went in for a routine ultrasound in her 26th week of pregnancy, she expected nothing but great news. The Manhattan Beach, Calif., nursing director was pregnant with her first baby and felt terrific. But her doctor found that Dressler’s uterus contained excessive amniotic fluid and that she was having 15 barely perceptible contractions an hour. Dressler was ordered to bed and given medications to try to stop her contractions and to reduce the amount of fluid.
Like Dressler, some 12 percent of pregnant women in the United States experience preterm labor, and the number of premature babies — those born before 37 weeks — is rising. According to the March of Dimes, 450,000 babies a year are born too soon, with prematurity contributing to more than 75 percent of newborn deaths. “Some of the increase is due to the greater number of twins and triplets, but some is because our treatments just aren’t that good yet,” says Michael Socol, M.D., professor of obstetrics and gynecology at Northwestern University Medical School in Chicago and past president of the Society for Maternal-Fetal Medicine. However, researchers are learning more about the causes of prematurity and, as a result, potential ways to prevent it.
Who is at risk?> The single biggest risk factor for premature labor is having experienced it previously, which triples or quadruples the chances. Women carrying twins have a 50 percent greater risk; smokers, first-time moms, and overweight, underweight and hypertensive women also are more prone. Having either a shorter-than-average cervix or a “weak,” or “incompetent,” cervix also increases risk. (A procedure known as circlage, which involves putting a stitch in a weak cervix, can help keep it from opening too soon.) Age has not proven to be a factor.
Researchers increasingly are finding links to stress and infection. Whether physical or psychological, stress definitely plays a role in early labor, says Donald Mattison, M.D., medical director for the March of Dimes. “Certainly, jobs requiring a lot of standing or walking without rest periods appear related,” he says, “but mentally demanding jobs may be as well.” Some investigators believe that by testing stress-hormone levels early in pregnancy, doctors may better predict who is at risk.
Researchers also believe that the same set of immunologic responses the body undergoes to fight infection can trigger labor. Vaginal infections, such as bacterial vaginitis, may be responsible for as many as 40 percent of preterm deliveries, says Charles Lockwood, M.D., a perinatologist and chairman of the department of obstetrics and gynecology at New York University.
Infections elsewhere in the body also can trigger premature labor. Several studies have found a link to periodontitis, or gum disease. If you need treatment for this during pregnancy, the safest time is probably during the second trimester, says Marjorie Jeffcoat, D.M.D., chairwoman of periodontics at the University of Alabama in Birmingham. In fact, you shouldn’t hesitate to take any antibiotic prescribed by your doctor.