"There may be other reasons why people would choose to space their pregnancy ... but we need people to understand that the timing of the interval between pregnancies has an effect on the outcome," Elena Fuentes-Afflick, MD, MPH, tells WebMD. Fuentes-Afflick, one of the co-authors of the study, is assistant professor of pediatrics at UCSF.
Fuentes-Afflick and her co-author, Nancy A. Hessol, MSPH, looked at nearly 300,000 single-baby births of Mexican-origin Hispanic and white women. They defined premature, or preterm birth, as a birth occurring before 37 completed weeks and full-term birth as a birth occurring between 38 to 42 weeks.
Women who got pregnant again less than 18 months after their previous pregnancy had a 14-47% risk of giving birth to a very premature or moderately premature infant. Also, those who conceived more than 59 months after their last child had a similar chance -- 12-45% -- of also delivering prematurely.
Women who had a short time between the end of one pregnancy and conception of the next also tended to use prenatal care less frequently, Fuentes-Afflick says. Perhaps the stress of closely spaced children and other factors may compete with the opportunity to take advantage of prenatal care, she suggests.
"The study confirms data from other institutions and countries that suggest delaying subsequent children for a certain amount of time is a good thing," Errol Norwitz, MD, PhD, says. However, Norwitz tells WebMD that despite the solid design of the study, other factors were not accounted for -- such as prior premature births, smoking, maternal health, marital status, and other conditions that tend to be risk factors for premature birth. Norwitz is an assistant professor in the division of maternal and fetal medicine in the obstetrics and gynecology department at Brigham and Women's Hospital and Harvard Medical School, both in Boston.
Fuentes-Afflick says that the study is by no means saying the interval between pregnancies is the most important or only risk consideration, but when the researchers adjusted for other maternal risk factors, the results did not change much. They were able to determine that the odds did increase for very premature and moderately premature infants among women who were Hispanic, were 15-17 years old, had nine to 11 years of education, had a previous premature infant, or used little or no prenatal care.
The prematurity risk after a delay of five years or longer was not easily explained. Infertility or other medical problems may have been part of the reason for the delay, Fuentes-Afflick suggests. "Although the women who waited longer tended to be older -- and maternal age certainly plays a role -- our bottom line is independent of maternal age, maternal education, and other factors that we were able to look at," she says.
- According to a new study, mothers should allow 18 to 59 months between the birth of one child and the conception of the next, in order to reduce the risk of delivering prematurely.
- The study also showed that women who had a short time interval between two pregnancies tended to use less prenatal care.
- Other factors that can contribute to premature delivery are maternal age, prior premature births, smoking, maternal health, and marital status.