Preterm labor

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Preterm labor

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 that cause her cervix to:

Open (dilate) at least .
Thin (efface) at least 80%.

Before 20 weeks, preterm labor that leads to delivery is considered a miscarriage (spontaneous abortion).

Credits

Author	Jan Nissl, RN, BS
Editor	Susan Van Houten, RN, BSN, MBA
Associate Editor	Tracy Landauer
Primary Medical Reviewer	Renée M. Crichlow, MD - Family Medicine
Specialist Medical Reviewer	Liisa Honey, MD, FRCSC - Obstetrics and Gynecology
Last Updated	August 7, 2006

Last updated:	August 07, 2006
Author:	Jan Nissl, RN, BS
Reviewed By:	Renée M. Crichlow, MD - Family Medicine, Liisa Honey, MD, FRCSC - Obstetrics and Gynecology
Editors:	Susan Van Houten, RN, BSN, MBA, Tracy Landauer

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