Redefining the Term

Revised Definition of Full-Term Pregnancy Based on NICHD Research

pregnant woman

The American Congress of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) announced that they are recommending the use of the label "term" in pregnancy be replaced by new gestational age designations.

According to the new designations1, full term will refer to 39 weeks through 40 weeks and 6 days of pregnancy. In the past, a pregnancy between 37 and 42 weeks was considered full term.

This change reflects findings from NICHD research about poorer health outcomes of babies born at 37 and 38 weeks of pregnancy—previously considered full term—compared to those born after 39 weeks. NICHD Director of Extramural Research Dr. Catherine Spong outlined much of this research in a May 2013 article published in the Journal of the American Medical Association External Web Site Policy detailing the results of a workshop lead by NICHD that produced the new designations.

For example, research shows that—compared to babies born at or after 39 weeks of pregnancy—babies born before 39 weeks are:

  • At greater risk of being admitted into the neonatal intensive care unit2
  • At a 20% greater risk of complications, including: breathing, feeding, and temperature2 problems; sepsis (severe blood infection)3; and cerebral palsy2
  • 5% more likely to have an intellectual or developmental disability2
  • At a 50% greater risk for death within the first year of life4

Mothers who deliver at or after 39 weeks of pregnancy typically have better outcomes than do mothers who deliver before 39 weeks.

The groups recommend that health care providers begin using the following new categories when discussing term pregnancies with their patients:

  • Early term: 37 weeks through 38 weeks and 6 days
  • Full term: 39 weeks through 40 weeks and 6 days
  • Late term: 41 weeks through 41 weeks and 6 days
  • Post-term: 42 weeks and beyond

According to ACOG and the SMFM, use of these new designations will lead to more consistent data and improved standards upon which to base clinical research. For the NICHD, these new definitions more accurately reflect the available research on infant health outcomes, which could contribute to better care for mothers and infants.

The NICHD’s National Child and Maternal Health Education Program (NCMHEP) offers information about the importance of waiting until at least 39 weeks—now defined as full term—to deliver a healthy pregnancy. The Program offers a video on why it’s worth it to wait until 39 weeks of pregnancy to deliver, as well as resources for expectant mothers and resources for health care providers.

The NICHD and the NCMHEP are encouraged by the revised designations and by the possibilities for improving care related to this change.

More Information


Originally posted: October 24, 2013


All NICHD Spotlights

  1. American College of Obstetricians and Gynecologists Committee on Obstetric Practice and Society for Maternal-Fetal Medicine. (2013). Committee Opinion No. 579. Definition of term pregnancy. Obstetrics & Gynecology, 122(5), 1139–1140. External Web Site Policy
  2. National Child and Maternal Health Education Program (NCMHEP). (no date). NCMHEP continuing medical education course: Raising awareness: Late preterm birth and non-medically indicated inductions prior to 39 weeks. External Web Site Policy
  3. Muzaffar, S. (2012). Early Elective Delivery (EED). Accessed April 19, 2013, from (PDF - 403 KB).
  4. Fleischman, A.R., Oinuma, M., & Clark, S.L. (2010). Rethinking the definition of "term pregnancy." Obstetrics & Gynecology, 116(1), 136-139. Accessed April 19, 2013, from External Web Site Policy
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