New Definitions of Full-Term Pregnancy: Why They Matter


A pregnancy is not full term until 39 weeks, according to a new set of definitions endorsed by the American Congress of Obstetrics and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine. This represents an important change from the old understanding under which pregnancy was considered full term from 37 weeks to 42 weeks.

The new set of definitions breaks down like this:

  • Early term: 37 weeks to 38 weeks and 6 days
  • Full term: 39 weeks to 40 weeks and 6 days
  • Late term: 41 weeks to 41 weeks and 6 days
  • Postterm: 42 weeks and beyond

In practical terms, what this means is that whereas for years mothers have been told that if they make it to 37 weeks they can assume their babies are ready to be born, those same babies will now be considered not yet full term for another two weeks.

Why Change the Definitions?

The change matters because, as the March of Dimes has been arguing and actively educating the public on, elective deliveries performed before 39 weeks without a medical reason consistently result in greater risks of health problems for the baby. These risks include problems with breathing as well as developmental issues.

Nevertheless, these early births—via induction or cesarean section—have risen to as many as 15 percent of births annually in the United States. The rate of early delivery is so high because the risks are not widely understood, because births are scheduled for reasons of health-care provider convenience, and because estimated due dates are often miscalculated, resulting in the mistaken belief that a baby is to term when it really is not yet.

The new definitions should encourage physicians to practice greater patience around the end of pregnancy. In most cases, spontaneous labor is the best way to determine the healthiest time for birth. It does, however, remain the case that there are some health conditions for which early induction is medically indicated, but in general labor should be allowed to start on its own.

The new definitions are good news not only for babies, but also for mothers. Not only is carrying to full term less likely to pose the health problems associated with prematurity in the baby, but the possibility of more spontaneously initiated labors would mean fewer labors via induction or surgery. Both of these interventions are accompanied by health risks to the mother, including more painful contractions, risk of infection, uterine rupture, and the possibility of cascading interventions in which ultimately induction will not work and the major surgery that is cesarean section will become necessary.

Part of a Larger Trend

The new definitions seem to be in line with a shift signaled by, among other things, a blog post published in March by ACOG President James T. Breeden in which he argued that “a vaginal birth that occurs after the natural onset of labor is ideal” and that both cesarean sections and labor induction should be limited to cases of medical necessity.

As Miriam Pérez commented at RH Reality Check in April, “I’m glad to see ACOG taking such a bold stance in supporting ‘mother nature’s’ role in the beginning of labor, but I know that it may take a long time for these recommendations to actually affect the use of inductions and preterm c-sections as parts of standard obstetrical practice.”

The new definitions hopefully will be a catalyst for a cultural shift toward encouraging labor to begin on its own.

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  • Arekushieru

    Sorry, but I believe that when a woman requests early delivery, limiting her right to do so only when ‘medically necessary’, actually harms the woman and, thus, the baby’s health. Miriam’s comment is rather disappointing, too. Just because a woman CAN do something doesn’t mean she SHOULD. It contradicts Amanda’s own article about women’s health care being more than merely keeping women alive. Thanks.

    • Sarah Whedon

      Thanks for your thoughtful comment. I agree that women should be empowered to make decisions about their own pregnancies and births. I do think there’s a bit of a straw man here because the dangerously high rates of inductions and cesarean deliveries in the U.S. are not primarily driven by maternal request. I remain cautiously hopeful that the new definitions will help care providers to better inform moms so that together they can make better decisions in each individual case.

      • Arekushieru

        I SO totally 100% agree, Sarah. Thanks for YOUR thoughtful comment. It’s very much appreciated! :)

  • John H

    Personally, I’ve always found c-section delivery to be fascinating from an socio-legal perspective. I would classify it as very-late-term abortion: it’s a medical intervention that ends pregnancy, it just generally involves a viable fetus that can (and does) survive the procedure (the use of the term “elective delivery” instead of “abortion” has definite political implications). As a supporter of the full bodily autonomy of people who can become pregnant (actually, everyone, though it’s most often people who can become pregnant who have their bodily agencies attacked), I’m in favor of the right to end a pregnancy at any point without restriction, whether such termination is likely to result in a viable infant or not. As such, while it might be a good idea to recommend to women interested in the health of their fetuses/infants above all else that they not end their pregnancies before going into labor or that they opt for vaginal delivery, any attempts to actually restrict ‘early’ elective delivery/late-term abortion are unacceptable.

    • Arekushieru

      I agree with your last comment, wholeheartedly, @disqus_iQFBMI7lGC:disqus! Case in point: I have a cousin who was married to, and is now currently in the process of divorcing, a woman whom my entire family felt they could absolutely not care for. Anyways, she and my cousin have two children. In her last pregnancy, my cousin’s estranged wife opted to deliver early. While many of my family would have regarded her decision as inappropriate, I absolutely supported her decision, in this case.

      But, I don’t classify a c-section delivery as an abortion. To me, an abortion is the termination of a pregnancy before a fetus is entirely extracted from the host’s body.

    • lady_black

      Going into labor could have killed me, and my son… in short order. Why don’t we just allow obstetric decisions to be made by the woman and her doctor with the ultimate goal of getting HER through it safely, and hopefully with a healthy baby. But her life is the first consideration, always.

  • Origami_Isopod

    “Sarah Whedon, Ph.D. is chair of the Department of Theology and Religious History at Cherry Hill Seminary, founding editor of Pagan Families, and the author of Birth on the Labyrinth Path: Sacred Embodiment in the Childbearing Year. She is an ALACE-trained birth doula and a Bay Area Doula Project-trained abortion doula, and she’s currently working to launch the Boston Doula Project.”

    LOL, what a pile of woooooooooo.

    • colleen2

      Sorry this blog disappoints someone your high standards and gigantic sense of entitlement. Perhaps you should read Jill Stanek’s blog, I understand that she has a nursing degree of some sort.

      • Origami_Isopod

        Well, that was a pointless and stupid reply. It’s rather appalling, though, that you think it’s “a gigantic sense of entitlement” to expect people commenting on medical issues to, you know, be medical professionals.

        • Arekushieru

          Perhaps Colleen2 was responding to the way you dismiss anything that
          doesn’t have a medical credential attached to it as New Age claptrap.
          Just because it is a medical issue written by someone who isn’t a medical professional, shouldn’t garner scorn for ANYTHING other than the content in it you happen to disagree with. Besides, people on this blog regularly write about medical issues without having a medical credential of any kind. So, do you only attack those that you agree with? Sorry, but that IS an attitude that is normally associated with right-wingers and Republicans. Kthx.

        • colleen2

          I have no interest in further conversation with you cmarie.