Prepregnancy Obesity and Birth Outcomes

24 Pages Posted: 18 May 2015

See all articles by Susan L. Averett

Susan L. Averett

Lafayette College - Department of Economics & Business

Erin Fletcher

University of Colorado at Boulder; Gettysburg College; Lafayette College - Department of Economics & Business


We investigate the association between prepregnancy obesity and birth outcomes using fixed effect models comparing siblings from the same mother. A total of 7,496 births to 3,990 mothers from the National Longitudinal Survey of Youth 1979 survey are examined. Outcomes include macrosomia, gestational length, incidence of low birthweight, preterm birth, large and small for gestational age (LGA, SGA), c-section, infant doctor visits, mother's and infant's days in hospital post-partum, whether the mother breastfed, and duration of breastfeeding. Association of income outcomes with maternal pre-pregnancy obesity was examined using Ordinary Least Squares (OLS) regression to compare across mothers and fixed effects to compare within families.In fixed effect models we find no statistically significant association between most outcomes and prepregnancy obesity with the exception of LGA, SGA, low birth weight and preterm birth. We find that prepregnancy obesity is associated with a with lower risk of low birthweight, SGA, and preterm birth but controlling for prepregnancy obesity, increases in GWG lead to increased risk of LGA. Contrary to previous studies, which have found that maternal obesity increases the risk of c-section, macrosomia and LGA, while decreasing the probability of breastfeeding, our sibling comparison models reveal no such association. In fact, our results suggest a protective effect of obesity in that women who are obese prepregnancy have longer gestation lengths, and are less likely to give birth to a preterm or low birthweight infant.

Keywords: infant health, birth outcomes, BMI, maternal obesity, gestational weight gain

JEL Classification: I12, J13

Suggested Citation

Averett, Susan and Fletcher, Erin, Prepregnancy Obesity and Birth Outcomes. IZA Discussion Paper No. 9052, Available at SSRN: or

Susan Averett (Contact Author)

Lafayette College - Department of Economics & Business ( email )

Easton, PA 18042
United States
610-250-5307 (Phone)
610-250-8961 (Fax)

Erin Fletcher

University of Colorado at Boulder ( email )

1070 Edinboro Drive
Boulder, CO 80309
United States

Gettysburg College ( email )

United States

Lafayette College - Department of Economics & Business ( email )

Easton, PA 18042
United States

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