New (And Hopefully Improved) Definition of Term Pregnancy

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Figuring out when a pregnancy is “term” should become a little easier, thanks to new criteria released by obstetricians and gynecologists (OB-GYNs).

In recent years, expectant women are more focused on what term pregnancy actually means, thanks to the increased reliability and safety of Cesarean sections, which makes it possible to deliver babies surgically. While intended for medical reasons only, the operation has become popular with mothers who are eager to deliver as soon as their pregnancy is considered “over.” Traditionally, term pregnancy referred to the period three weeks before to two weeks after an estimated delivery date, and indicates the window during which a baby can be born.

But research increasingly shows that physical and mental development differ considerably depending on when babies are born within this time frame. Those five weeks are critically important for proper development, and babies born too early are at higher risk of conditions such as respiratory problems and hypoglycemia. So to improve birth outcomes, major OB-GYN groups collaborated to announce a new definition for term pregnancy that separates the period into four distinct categories.

The categories are as follows:

Early Term: Between 37 weeks 0 days and 38 weeks 6 days
Full Term: Between 39 weeks 0 days and 40 weeks 6 days
Late Term: Between 41 weeks 0 days and 41 weeks 6 days
Postterm: Between 42 weeks 0 days and beyond

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“We wanted there to be no confusion among providers or patients [who assume] that outcomes were uniform between 37 and 42 weeks. We are concerned that by applying a single label to them — the label of ‘term’ — some might come to that conclusion,” says Dr. Jeffrey L. Ecker, chair of the American College of Obstetricians and Gynecologists’ (ACOG) Committee on Obstetric Practice. ACOG, and the Society for Maternal-Fetal Medicine (SMFM) wrote the joint opinion paper published in the journal Obstetrics & Gynecology.

“Increasingly it has been demonstrated in good studies with good research that outcomes between 37 to 39 weeks, for example, are different and worse than outcomes between 39 and 41 weeks,” he says. Most of these differences involve issues with respiratory development. For instance, research published in the New England Journal of Medicine showed that babies born at 37 weeks were at a greater risk for poor respiratory health, newborn sepsis and hypoglycemia compared to babies born at 38 weeks. The babies born earlier also needed more mechanical ventilation, were more likely to be admitted to the neonatal ICU, and hospitalized for five days or more.

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By stratifying term pregnancy, the experts also hope to highlight the fact that elective delivery should not occur before 39 weeks. “I think it just brings clarity to physicians that these five weeks are critical and that you should not deliver a patient electively before they go into labor spontaneously on their own unless there is medical, maternal or fetal indications of a delivery,” says Dr. Mari-Paule Thiet, the director of the Division of Maternal-Fetal Medicine at the University of California, San Francisco.

At first, the four different time frames–specific to the day–may appear more confusing, but ACOG and Thiet believe they will ultimately give women a clearer picture of their baby’s developmental status. “Patients know that due date. They circle it and they know the exact date that that baby should come. In the past we gave that gray zone of five weeks for it to come and said it could come any time within that window, and it’s all the same..” The new definition, Thiet says, should telescope that window and give women a more realistic sense of when it’s time for them to delivery. “I think it’s good that now patients can think, ‘ok, this is really my two weeks until due date week. I might deliver before my due date, but I hope I don’t,'” she says.

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The four-stage definition should also help doctors and those conducting research on the effects of delivery time on development to share standard criteria so study findings can be more valuable for OB-GYNs treating patients. “Because we do recognize that outcomes are different, by adding specific labels, it allows doctors and patients to speak specifically about what they anticipate, and for the language used to be consistent among different doctors and practices so that everyone will apply ‘early term’ to 37 to 39 weeks instead of one hospital saying, ‘early term’ and another hospital saying ‘short of term.’ Everyone will speak the same language,” says Ecker.

ACOG says the new labels will be incorporated in all of their literature and documents, both printed and on the web, so they can be applied as quickly as possibly by OBGYNs and their patients. There may be some confusion at first, as some continue to use their own terms for term pregnancy, but Ecker is confident that more doctors appreciate that not all delivery dates are equal.