Inter-Pregnancy Change in Body Mass Index and Risk of Preterm Birth

Sarah K Littlejohn, The University of Texas School of Public Health

Abstract

Preterm birth (PTB), or birth of an infant before 37 completed weeks of gestation, is a leading cause of infant morbidity and accounts for 36% of infant deaths in the United States. When compared to women with prepregnancy BMI in the normal range, women who are underweight (BMI<18.5 kg/m 2) or obese (BMI>30.0 kg/m2) have been found to be at an increased risk of PTB, yet the mechanisms behind this association are not fully understood. To improve the understanding of the association between prepregnancy BMI and PTB, we evaluated the association between interpregnancy change in BMI (IPC-BMI) and PTB. Infants born without a birth defect in Texas between 2006 and 2012 were randomly selected and then linked to an older sibling born between 2005 and 2012. In primary analyses, multivariable logistic regression was used to assess the association between IPC-BMI and PTB. This association was assessed in the full study sample and within strata defined by prepregnancy BMI at the sibling pregnancy (BMI-sib). In secondary analyses, we considered IPC-BMI as a continuous variable and used linear regression to evaluate the association between IPC-BMI and gestational age. The final sample size included 2,481 infants with linked siblings with 255 (10.3%) of the index infants born preterm. Among mothers in the sample, the mean IPC-BMI was an increase of 1.12 kg/m2. After controlling for BMI-sib, maternal smoking, maternal race/ethnicity and gestational weight gain, there was a statistically significant association between a decrease in BMI by more than 1 kg/m 2 between pregnancies and an increase in odds of PTB (aOR: 1.88, 95% CI: 1.26, 2.81). There is evidence for a significant linear trend (p=0.001) between increasing IPC-BMI categories and decreasing odds of PTB. When stratified by BMI-sib, the association between a decrease in BMI and an increase in odds of PTB was statistically significant only among normal weight mothers (aOR: 1.87, 95% CI: 1.13, 3.07). Since, IPC-BMI is a modifiable risk factor, the association between IPC-BMI and preterm birth provides further evidence of the value of interventions to maintain or achieve a healthy weight prior to pregnancy.

Subject Area

Obstetrics|Public health|Epidemiology

Recommended Citation

Littlejohn, Sarah K, "Inter-Pregnancy Change in Body Mass Index and Risk of Preterm Birth" (2018). Texas Medical Center Dissertations (via ProQuest). AAI10789065.
https://digitalcommons.library.tmc.edu/dissertations/AAI10789065

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