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Overview of preterm labor and birth

Charles J Lockwood, MD, MHCM
Section Editor
Susan M Ramin, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Preterm birth refers to a delivery that occurs before 370/7ths weeks of gestation. It may or may not be preceded by preterm labor. Although term pregnancy has been defined as 370/7ths to 416/7ths weeks of gestation, the period 370/7ths to 386/7ths weeks should be considered ‘early term’ because neonates born in this gestational age range have higher neonatal morbidity and mortality than infants born at ‘full term’ from 390/7ths to 406/7ths weeks [1,2].


Classification — Subtypes of preterm birth are variably defined.

By gestational age:

World Health Organization [3]:

Moderate to late preterm: 32 to <37 weeks


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Literature review current through: Apr 2015. | This topic last updated: Apr 22, 2015.
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