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Term Pregnancy: A Period of Heterogeneous Risk for Infant Mortality

Reddy, Uma M. MD, MPH; Bettegowda, Vani R. MHS; Dias, Todd MS; Yamada-Kushnir, Tomoko MPH, MS; Ko, Chia-Wen PhD; Willinger, Marian PhD

doi: 10.1097/AOG.0b013e3182179e28
Original Research

OBJECTIVE: To estimate the trend of maternal racial and ethnic differences in mortality for early-term (37 0/7 to 38 6/7 weeks of gestation) compared with full-term births (39 0/7 to 41 6/7 weeks of gestation).

METHODS: We analyzed 46,329,018 singleton live births using the National Center for Health Statistics U.S. period-linked birth and infant death data from 1995 to 2006. Infant mortality rates, neonatal mortality rates, and postneonatal mortality rates were calculated according to gestational age, race and ethnicity, and cause of death.

RESULTS: Overall, infant mortality rates have decreased for early-term and full-term births between 1995 and 2006. At 37 weeks of gestation, Hispanics had the greatest decline in infant mortality rates (35.4%; 4.8 per 1,000 to 3.1 per 1,000) followed by 22.4% for whites (4.9 per 1,000 to 3.8 per 1,000); blacks had the smallest decline (6.8%; 5.9 per 1,000 to 5.5 per 1,000) as a result of a stagnant neonatal mortality rate. At 37 weeks compared with 40 weeks of gestation, neonatal mortality rates increase. For Hispanics, the relative risk is 2.6 (95% confidence interval [CI] 2.0–3.3); for whites, the relative risk is 2.6 (95% CI 2.2–3.1); and for blacks, the relative risk is 2.9 (95% CI 2.2–3.8). Neonatal mortality rates are still increased at 38 weeks of gestation. At both early- and full-term gestations, neonatal mortality rates for blacks are 40% higher than for whites and postneonatal mortality rates 80% higher, whereas Hispanics have a reduced postneonatal mortality rate when compared with whites.

CONCLUSION: Early-term births are associated with higher neonatal, postneonatal, and infant mortality rates compared with full-term births with concerning racial and ethnic disparity in rates and trends.


For all races and ethnicities, early-term births are consistently associated with higher neonatal, postneonatal, and infant mortality rates when compared with full-term births. SUPPLEMENTAL DIGITAL CONTENT IS AVAILABLE IN THE TEXT.

From the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; the March of Dimes, White Plains, New York; and the U.S. Food and Drug Administration, Silver Spring, Maryland.

The authors thank Ms. Christine Rogers for her assistance with the figures and tables in this article.

Corresponding author: Uma M. Reddy, MD, MPH, 6100 Executive Boulevard, Room 4B03F, Bethesda, MD 20892-7510; e-mail.

Financial Disclosure The authors did not report any potential conflicts of interest.

© 2011 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.