A study in the June issue of Obstetrics & Gynecology redefined the parameters of a full-term pregnancy. The research found that infant mortality rates are cut in half when the baby isn't born until at least 39 weeks, rather than 37 weeks.
Thirty-seven weeks had previously been considered full-term, although a complete pregnancy technically lasts 40 weeks. The finding that waiting an extra two weeks to deliver can make a difference in a baby's survival added heft to the increasingly vocal public-health message that women should not schedule delivery before 39 weeks. "Up until the last several years, we thought term pregnancies between 37 and 41 weeks were the same," says Alan Fleischman, medical director at the March of Dimes. "This is not the case. It's a biological continuum. The new data makes us pause and realize we ought not intervene unless there's a very good medical reason."
Researchers at the National Institutes of Health, the March of Dimes and the U.S. Food and Drug Administration looked at mortality rates for babies born between 37 and 40 weeks. They found that babies born at 37 weeks had twice the risk of death as 40-weekers, regardless of race or ethnicity. According to 2005 data, the infant-mortality rate was 3.9 per 1,000 babies born at 37 weeks, compared with 1.9 deaths for every 1,000 live births for babies born at 40 weeks. "Mortality is the tip of an iceberg, so there are large numbers of babies who don't die but are sick and require neonatal intensive-care interventions and hospitalizations that they would not have needed if they were born a few weeks later," says Fleischman.