Preterm labor occurs during pregnancy when the uterus regularly contracts before the 37th week of pregnancy, causing the cervix to open (dilate) and thin (efface).
Symptoms of preterm labor include pelvic or lower abdominal pressure; a persistent, dull ache in the lower back; menstrual-like cramps (with or without diarrhea); a change in the type or amount of vaginal discharge (sometimes a leak or gush of fluid); and regular or frequent tightening of the uterine muscle, often painless.
Early symptoms of preterm labor often are hard to diagnose. Commonly, the uterus will contract before true labor. 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.
Before 20 weeks of pregnancy, preterm labor that leads to delivery is considered a miscarriage (spontaneous abortion). Very few premature infants will survive preterm birth at 23 weeks. Many hospitals do not resuscitate newborns born until 24 weeks of pregnancy because the chance of survival is extremely low.
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