LATE FOR THE PARTY
Babies are regarded as full-term between 37 and 42 weeks of gestation. But one in ten infants arrives after 42 weeks. "Remember, you're considered post-term at 42 weeks -- not at 40," notes Iffath Hoskins, M.D., chief of obstetrics at the New York University Downtown Hospital. In fact, since a due date is at best an educated guess, many "overdue" babies aren't really late at all. Even if the due date is right, doctors aren't sure why some babies need to gestate for longer than others, but they do know that first-time mothers tend to deliver later than veteran moms.
While more than 90 percent of post-term babies are delivered safely, the risk of complications tends to increase as pregnancy stretches on, according to Kathryn Moyer, M.D., an ob-gyn in Santa Monica, CA. One reason: The placenta, which transports oxygen and nutrients to the fetus, may function less efficiently after 40 weeks. In addition, babies left to grow inside the womb can become too large to pass safely through the birth canal, so a c-section becomes more likely.