Generations of mothers-to-be have heard that babies born any time
between 37 and 42 weeks of pregnancy were "at term" - neither too early
nor too late. But that is now officially outdated wisdom, two leading
medical groups said Tuesday.
A pregnancy is "full term" only in
the narrower two-week window that starts at 39 weeks, under new
definitions published in the journal Obstetrics & Gynecology
and endorsed by the American College of Obstetricians and Gynecologists
and the Society for Maternal-Fetal Medicine. The groups say babies born
within those two weeks do best. Babies born two weeks before or one week
after that window, at "early term" or "late term," face a few more
risks, they say.
The biggest reason the terminology needs to
change is to discourage doctors and patients from scheduling medically
unnecessary deliveries - by induction or C-section - before 39 weeks,
says Jeffrey Ecker, a specialist in maternal-fetal medicine at
Massachusetts General Hospital, Boston. He chairs the college's
committee on obstetric practice.
The new definitions are based on
recent research. The old terminology "was based on the general
observation that babies born after 37 weeks tended to do quite well,"
Ecker says. That's still true, he says, but doctors know now that babies
born at 39 and 40 weeks do better and that risks rise again after 41
"Language and labels matter," he says, and the changes will help doctors better communicate the latest science to patients.
how expectant mothers should now expect doctors to describe the last
possible weeks of pregnancy (counted from the first day of a woman's
last menstrual period, but sometimes adjusted after an ultrasound):
• Early term: Between 37 weeks 0 days and 38 weeks, six days
• Full term: Between 39 weeks and 40 weeks, six days
• Late term: Between 41 weeks and 41 weeks, six days
• Post term: 42 weeks and beyond
definitions were developed at a workshop in 2012 that included
representatives from the National Institute of Child Health and Human
Development and other medical groups. Details from the workshop were published in the journal JAMA earlier this year.
the official endorsement by doctors who deliver babies is "incredibly
important," says Edward McCabe, medical director of the March of Dimes.
"In the past, when a woman made it past the 37-week goal line, she was
home ... This moves the goal line."
A 2009 survey of 650 women who had recently given birth, also published in Obstetrics & Gynecology,
found plenty of confusion about where that goal line was. When asked
when a pregnancy reached "full term," 24% said 34-36 weeks, 51% said
37-38 weeks and just 25% said 39-40 weeks.
Those attitudes helped
explain why early elective deliveries were continuing to rise even after
studies revealed risks for babies, including more breathing and feeding
problems and a small, but increased, risk of death.
Groups including the March of Dimes have been working for several years to educate women about those risks. Many hospitals now have programs in place to stop elective early deliveries.
efforts have had a "significant effect," but the new terminology will
help too, says Elliott Main, medical director of the California
Maternal Quality Care Collaborative. "It's really nice for doctors to be
able to say this is a national effort and we are trying to improve
outcomes. Mothers want better outcomes for their kids."
cautions on early deliveries "should not panic women who go into labor
spontaneously at 37 weeks," or who need to deliver early because they or
their babies have medical problems, Ecker says. Early delivery can be
justified by conditions from dangerously high blood pressure in a mother
to poor growth in a baby, he says. "We are not saying deliveries before
39 weeks should be a 'never' event, but we are saying there should be a
Main says one reason planned early deliveries have
higher risks is that doctors and patients sometimes miscalculate due
dates. Babies themselves are better judges, he says, as evidenced by the
fact that women who go into spontaneous labor at 37 or 38 weeks tend to
have healthier babies than those who choose such early deliveries.
"Spontaneous labor set off by the baby is sign that the baby is really ready to be born," he says.