Fall 2012

Time for Delivery

Babies who stay in the womb longer seem to do better on tests of intelligence later

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Illustration: Phil Wrigglesworth

It can be a good idea to take your time with life’s great events. An extensive new study has found that babies who stayed in their mothers’ wombs longer seemed to do better on tests of intelligence later.

The study, published in Pediatrics in early July, showed that babies born at 37 or 38 weeks scored slightly worse on third-grade English and math tests than their counterparts born at 39 to 41 weeks. (A typical pregnancy is 40 weeks.) The finding, based on the birth records of 128,000 babies born in New York City between 1988 and 1992, has implications for doctors and parents who often prefer early deliveries, either for the sake of convenience or because of a hint of complication with the pregnancy.

Jonathan Davids, professor of pediatrics and chief of newborn medicine at the Floating Hospital for Children at Tufts Medical Center, who was not involved in the research, confirms that the womb is really the best place for a baby to be. “The message is that unless you really feel that there’s an irreversible or really dangerous thing going on, you should wait until at least 39 weeks to deliver,” he told WBUR’s CommonHealth blog.

The new finding aligns with some recent dramatic shifts in thinking. About a decade ago, Harvard hospitals decided to start delivering some babies via C-section at 38 weeks to improve scheduling flexibility and spread out the demand for operating rooms, according to Tamara Takoudes, a clinical instructor at Harvard Medical School. More recently, however, those same hospitals went back to the 39-week rule after data suggested more babies were ending up in intensive care, she said in the WBUR blog.

Kimberly Noble, an assistant professor of pediatrics at Columbia University Medical Center and one of the authors of the Pediatrics paper, cautioned that the study did not prove that early birth caused lower test scores. It’s not that simple. Although researchers tried to account for as many factors as they could in the study, including socioeconomics, birth weight, age of the mother and the number of C-sections, for example, some unidentified common factor might have caused both, she noted.

Noble tells parents who do have to deliver at 37 or 38 weeks not to worry about their child’s eventual third-grade test performance. There’s plenty of time, she says, to make up whatever small deficits come from being a week or two early.

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