March 21, 2000 (New York) -- Only a small percentage of women who give birth prematurely the first time will deliver their second babies prematurely, according to a study in the Journal of the American Medical Association. Those at highest risk for a second premature delivery are typically black teen-agers.
Study author Melissa M. Adams, PhD, tells WebMD that the research provides new information on African-American women. In addition, she says, it "can provide some comfort to women and to practitioners who are counseling these women that having a first preterm delivery doesn't necessarily mean that you're going to have a preterm delivery in your second pregnancy." Adams is with the division of reproductive health at the CDC in Atlanta.
The majority of white and African-American women whose first pregnancies resulted in premature deliveries (less than 37 weeks of pregnancy) carried their second pregnancies to term. But women who had delivered a first child very prematurely (after less than 31 weeks of pregnancy) and who were under 18 at the time of their second pregnancies had twice the risk of having a second very premature infant compared to a similar group who were 20 to 49 years old at their second delivery.
The study looked at the records of more than 100,000 white women and 55,000 black women 49 and younger.
"The shorter your first pregnancy was, the higher your likelihood of having a preterm delivery in your second pregnancy," Adams says. Among all women whose first deliveries were preterm, 20% of white women and 26% of black women delivered premature infants in their second pregnancies. The risk increased among those who delivered very premature infants, after 20 to 27 weeks. In these cases, 29% of white women and 37% of black women had preterm deliveries in their second pregnancies.
Among black women under 18 who had a very premature first delivery, nearly half delivered prematurely in the second pregnancy: 22% very prematurely and 26% moderately so. For young white women, the corresponding percentages were 15% and 26%.
Many women worry that they may not only have a second premature birth, but that the baby may be even more premature than the first one. That risk is small, but exists, the study shows. Among women whose first child was delivered at 32 to 36 weeks, the percentage who had a second child at 20 to 31 weeks was 2% for white women and nearly 4% for black women.
Researchers do not know all the reasons why some women are more at risk for giving birth prematurely. Some factors that can contribute to the risk include smoking, using drugs or alcohol during pregnancy, and not gaining enough weight.
Another risk factor for prematurity or for delivering a small infant is getting pregnant within six months of a prior pregnancy. In the study, African-American women whose first child was delivered at 32 to 36 weeks and who had intervals between their pregnancies of more than 47 months had a lower risk of delivering another similarly premature baby. Black women whose first newborns had moderately low birthweights and who had intervals between pregnancies of less than 11 months had a moderately higher risk for having a second low-birthweight child. This may reflect poor growth, prematurity, or both.
Women should tell their primary care providers about their obstetric history and notify them when they are considering getting pregnant. With new diagnostic tests and ultrasound, and with the availability of specialists in maternal-fetal medicine, doctors can more easily determine who is at increased risk for premature birth, who is in preterm labor instead of false labor, and who should be treated before and during pregnancy.