Maternal Pre-pregnancy BMI, Gestational Weight Gain, and Infant Birth Weight: A Within-Family Analysis in the United States

In the United States, the high prevalence of unhealthy preconception body weight and inappropriate gestational weight gain among pregnant women is an important public health concern. However, the relationship among pre-pregnancy BMI, gestational weight gain, and newborn birth weight has not been well established. This study uses a very large dataset of sibling births and a within-family design to thoroughly address this issue. The baseline regression controlling for mother fixed effects indicates maternal preconception overweight, preconception obesity, and excessive gestational weight gain significantly increase the risk of having a high birth weight baby, while underweight before pregnancy and inadequate gestational weight gain increase the low birth weight incidence. The benchmark results are robust in a variety of sensitivity checks. Since poor birth outcomes especially high birth weight and low birth weight have lasting adverse impacts on newborn’s health, education and socio-economic outcomes later in life, the findings of this research suggest promoting healthy weight among women before pregnancy and preventing inappropriate weight gain during pregnancy can generate significant intergenerational benefits. Key Words: Pre-pregnancy BMI; Gestational weight gain; Birth weight; High birth weight; Low birth weight