Abstract
BackgroundMaternal prepregnancy body mass index (BMI) is associated with several infant outcomes, but it is unclear whether these associations reflect causal relationships. We conducted a study of interpregnancy change in BMI (IPC-BMI) to improve understanding of the associations between BMI and large for gestational age (LGA), small for gestational age (SGA), and preterm birth (PTB).MethodsBirth certificate data from 2481 linked sibling pairs (Texas, 2005–2012) were used to estimate IPC-BMI and evaluate its association with LGA, SGA, and PTB in the younger sibling of the pair. Multivariable logistic regression was used to estimate adjusted odds ratios (aOR) and 95% confidence intervals (CI) using data from the full sample and within strata defined by prepregnancy BMI for the older sibling.ResultsOn average, women gained 1.1 BMI units between pregnancies. In the full sample, interpregnancy BMI decreases were associated with reduced odds of LGA and increased odds of SGA and PTB (IPC-BMI < -1 versus 0 to < 1: LGA aOR 0.7, 95% CI 0.4, 1.1; SGA aOR 1.6, 95% CI 1.0, 2.7; PTB aOR 1.9, 95% CI 1.3, 2.8). In stratified analyses, similar associations were observed in some, but not all, strata. Findings for interpregnancy BMI increases were less consistent, with little evidence for associations between these outcomes and the most extreme IPC-BMI increases.ConclusionsThere is growing evidence that interpregnancy BMI decreases are associated with LGA, SGA, and PTB. However, taken as a whole, the literature provides insufficient evidence to establish causal links between maternal BMI and these outcomes.
Highlights
Maternal prepregnancy body mass index (BMI) is associated with several infant outcomes, but it is unclear whether these associations reflect causal relationships
Villamor and Cnattingius [2] noted that support for a causal relationship between maternal weight and an infant outcome would be strengthened by evidence that temporal changes in an individual’s weight are associated with the outcome and suggested change in prepregnancy BMI between successive pregnancies, or interpregnancy change in BMI (IPC-BMI), as a measure of temporal weight change
We found little evidence of an association between preterm birth (PTB) and interpregnancy BMI increase, which is consistent with the majority of studies that have combined data from both medically-indicated and spontaneous PTB [5, 15, 20, 21]
Summary
Maternal prepregnancy body mass index (BMI) is associated with several infant outcomes, but it is unclear whether these associations reflect causal relationships. Compared to the offspring of women with normal prepregnancy body mass index (BMI), the offspring of obese women are at higher risk of death, congenital malformation, preterm birth (PTB), and being large for gestational age (LGA) [1]. Whether these associations reflect causal influences or Villamor and Cnattingius [2] noted that support for a causal relationship between maternal weight and an infant outcome would be strengthened by evidence that temporal changes in an individual’s weight are associated with the outcome and suggested change in prepregnancy BMI between successive pregnancies, or interpregnancy change in BMI (IPC-BMI), as a measure of temporal weight change. PTB was omitted from the meta-analysis due to a lack of relevant data for calculating a pooled estimate for this outcome [8]
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