How To Tell When Labor Begins Preterm Labor Preterm labor is defined as regular contractions of the uterus resulting in changes in the cervix that start before 37 weeks of pregnancy. Changes in the cervix include effacement (the cervix thins out) and dilation (the cervix opens so that the fetus can enter the birth canal). When birth occurs between 20 weeks of pregnancy and 37 weeks of pregnancy, it is called preterm birth.
How to Tell When Labor Begins Your uterus may contract off and on before “true” labor begins. These irregular contractions are called false labor, or Braxton Hicks contractions. They are normal but can be uncomfortable at times. You might notice them more at the end of the day.
Differences between false labor and true labor
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Type of Change
False Labor
True Labor
Timing of contractions
Braxton Hicks contractions are often irregular and do not get closer together.
Come at regular intervals and, as time goes on, get closer together. Each lasts about 30-70 seconds.
Change with movement
Contractions may stop when you walk, rest or with a change of position.
Contractions continue, despite movement.
Strength of contractions
Usually weak (may be strong and then weak).
Increase in strength steadily.
Pain of contractions
Usually felt only in the front.
Starts in the back and moves to the front.
Labor and delivery
