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Preterm labor occurs during pregnancy when the
uterus starts to contract before the 37th week of
pregnancy, causing the
cervix to open (dilate) and thin (efface).
The length of a normal pregnancy is 37 to 42 weeks, measured from the
date of the mother's last menstrual period.
Early symptoms of
preterm labor often are hard to diagnose. The uterus normally begins to
contract around the 20th week of pregnancy. These early contractions (Braxton Hicks contractions) do not dilate or efface
the cervix but help prepare the uterus and fetus for labor. These contractions
can be mistaken for preterm labor.
Preterm labor is diagnosed in a
woman who is 20 to 37 weeks pregnant and has regular uterine contractions. This
means 4 or more in 20 minutes, or about 8 or more in 1 hour.
Before 20 weeks, preterm labor that leads to delivery is considered a
miscarriage (spontaneous abortion).
March 20, 2012
William H. Blahd, Jr., MD, FACEP - Emergency Medicine & H. Michael O'Connor, MD - Emergency Medicine
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