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Defining “Term” Pregnancy:  Recommendations From the Defining “Term” Pregnancy Workgroup

Catherine Y. Spong, MD
JAMA. 2013;309(23):2445-2446. doi:10.1001/jama.2013.6235.
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The national emphasis on reducing preterm birth, and the increase in scheduled deliveries, has created confusion around the definition of term gestation. The concept of “term” gestation provides guidance to clinicians and influences the public's perceptions about the optimal timing of delivery for a healthy pregnancy. Currently, a term birth is defined as a delivery that occurs neither preterm nor postterm. Because preterm is classically defined as delivery prior to 37 weeks following the onset of the last menstrual period and postterm as after 42 weeks, term has been conventionally defined as delivery between 37 and 42 weeks. The International Classification of Diseases defines term pregnancy as delivery between 37 weeks 0 days and 41 weeks 6 days.1,2

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Figure. Proposed Approach for Determination of Gestational Age
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If the LMP is known, an ultrasound obtained before 13 weeks 6 days with a crown-rump length corresponding to a gestational age within 5 days confirms the estimated due date based on menstrual dates. Conversely, the estimated due date should be based on the ultrasound if the difference between menstrual and ultrasound dates is 6 days or greater. For ultrasounds between 16 and 22 weeks, composite gestational age based on biometry should be within 10 days to confirm LMP dating, and the estimated due date should be changed only if the calculated gestational age difference is 11 days or greater. If the LMP is unknown, dating should be based on ultrasound, preferably in the first trimester. When performed by trained practitioners, the first ultrasound is the most accurate, and the pregnancy should not be redated based on a subsequent ultrasound.aBiometry based on biparietal diameter, abdominal circumference, and femur length.



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