When does labor usually start?

For most women, labor begins sometime between week 37 and week 42 of pregnancy. Labor that occurs before 37 weeks of pregnancy is considered premature, or preterm.1

Just as pregnancy is different for every woman, the start of labor, the signs of labor, and the length of time it takes to go through labor vary from woman to woman and even from pregnancy to pregnancy.

The primary sign of labor is a series of contractions (tightening and relaxing of the uterus) that arrive regularly. Over time, they become stronger, last longer, and are more frequent. Some women may experience false labor, when contractions are weak or irregular or stop when the woman changes positions. Women who have regular contractions every 5 to 10 minutes for an hour should let their health care provider know.

It is important to discuss labor and signs of labor with a health care provider early in pregnancy, before labor begins. Some providers may want a woman to wait until she has multiple signs of labor or is in "active" labor before coming to the hospital or birthing center.

Other signs of labor include:2

  • "Lightening." This term refers to when the fetus "drops," or moves lower in the uterus. This may happen several weeks or only a few hours before labor begins. Not all fetuses drop before birth. Lightening gets its name from the feeling of lightness or relief that some women experience when the fetus moves from the rib cage to the pelvic area. It allows some women to breathe more easily and more deeply and may provide relief from heartburn.
  • Increase in vaginal discharge. Called "show" or "the bloody show," the discharge can be clear, pink, or slightly bloody. This discharge occurs as the cervix begins to open (dilate) and can happen several days before labor or just as labor begins.

Labor contractions before 37 weeks of pregnancy are a sign of preterm labor. Women who notice regular, frequent contractions at any point in pregnancy should notify a provider or go to the hospital. Providers can check for changes in the cervix to see whether labor has begun. As needed, providers can also give women in preterm labor specialized care. Among women who experience preterm labor, only about 10% go on to give birth within a week.

Other signs of labor include:3

  • Change in vaginal discharge
  • Pain or pressure around the front of the pelvis or the rectum
  • Low, dull backache
  • Cramps that feel like menstrual cramps, with or without diarrhea
  • A gush or trickle of fluid, which is a sign of water breaking

Sometimes, if the health of the mother or the fetus is at risk, a woman's health care provider will recommend inducing or causing labor using medically supervised methods, such as medication.4

Unless earlier delivery is medically necessary or occurs on its own, waiting until at least 39 weeks before delivering gives mother and baby the best chance for healthy outcomes. During the last few weeks of pregnancy, the fetus's lungs, brain, and liver are still developing.5

The Is It Worth It? Initiative, from NICHD's National Child and Maternal Health Education Program, focuses on raising awareness of the importance of waiting until at least 39 weeks to deliver a baby, unless it is medically necessary to deliver earlier.


  1. Fleischman, A. R., Oinuma, M., & Clark, S. L. (2010). Rethinking the definition of “term pregnancy.” Obstetrics and Gynecology, 116(1), 136–139.
  2. American College of Obstetricians and Gynecologists. (2011). FAQ: How to tell when labor begins. Retrieved February 13, 2017, from http://www.acog.org/Patients/FAQs/How-to-Tell-When-Labor-Begins
  3. American College of Obstetricians and Gynecologists. (2016). FAQ: Preterm (premature) labor and birth. Retrieved July 17, 2017, from https://www.acog.org/Patients/FAQs/Preterm-Labor-and-Birth
  4. American College of Obstetricians and Gynecologists. (2012). FAQ: Labor induction. Retrieved February 13, 2017, from http://www.acog.org/Patients/FAQs/Labor-Induction
  5. National Child and Maternal Health Education Program. (2013). Moms-to-be: Let baby set the delivery date. Retrieved February 13, 2017, from https://www.nichd.nih.gov/ncmhep/initiatives/is-it-worth-it/Pages/moms.aspx
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