Pediatricians who specialize in the treatment of premature infants have made remarkable gains. Twenty years ago, a baby born 12 weeks early in the United States would have had little chance of surviving; today, that baby's chances of survival are more than 90%.
In spite of this progress, the issue of prematurity remains a great concern because the number of children born too early is on the rise. Between 1981 and 2002, the rate of premature births in the United States increased almost 30%.
The challenge of decreasing these numbers has fallen to obstetricians. Many of the things they've been trying haven't worked, but a new approach, using the hormone progesterone, offers some promise.
The most common cause of premature delivery is preterm labor, or regular contractions beginning before 37 weeks. In most cases, it's impossible to identify what causes the contractions. "There are probably several different causes," says Jennifer Niebyl, a professor of obstetrics and gynecology at the University of Iowa in Iowa City. In some women, the contractions may be related to an overstretching of the uterus; in others, an infection could trigger them.
A number of things are known to increase the likelihood that preterm labor will occur. One group of women at high risk are those who have previously given birth to a premature infant. Women who are pregnant with twins or triplets have a much greater chance of delivering prematurely than women carrying a single child. (Approximately half of all twin births end before 37 weeks; nearly all triplet births end prematurely.)
By identifying women at risk, doctors hope to be able to prevent contractions from starting too early and to stop them quickly if they do. Unfortunately, this is easier said than done.
Many interventions that have been widely used to date are now believed not to work. Bed rest, for example, is considered by most experts to be largely ineffective. In spite of this, bedrest is still frequently prescribed for women with threatened preterm labor. There's no evidence to suggest that it reduces the risk of preterm birth; in twin pregnancies, it may actually increase it. Even medications that help stop contractions once they have started appear to postpone delivery by only a day or two.
One treatment that is gaining favor, however, is the use of progesterone. A study published last year in the New England Journal of Medicine found that women with a history of premature delivery who received a weekly injection of progesterone beginning at 16 to 20 weeks of pregnancy had significantly fewer premature births than women given a placebo -- an ineffective pill. Treatment reduced the risk of delivery at less than 37 weeks of pregnancy by 34%; the risk of delivering before 32 weeks was decreased by 42%.
The idea, says Niebyl, is that progesterone prevents the uterine contractions that lead to preterm labor.
In October 2003, the American College of Obstetricians and Gynecologists acknowledged that progesterone may be used to reduce preterm births in women with a history of early delivery. Because it has not been tested in other "high-risk" women, progesterone is not currently recommended for them.
"Once we get a better sense of what causes preterm labor, we'll better know how to treat it," Niebyl says. For now, the most important things a pregnant woman can do are learn to detect contractions and other signs of labor (such as pelvic pressure, vaginal discharge and back pain) and get to a hospital with a newborn intensive care unit quickly if she suspects she might deliver prematurely.
Dr. Valerie Ulene is a board-certified specialist in preventive medicine practicing in Los Angeles. She can be reached by e-mail at firstname.lastname@example.org.