The Impact of Increased Pre-Pregnant Adiposity on Birth Weight Indices

A secondary data analysis was undertaken to analyze risk in term singleton infants of non-diabetic women for high birth weight indices: large-for-gestational-age (LGA), birth weight z-scores and ponderal index. Multiple regression analyses using logistic, linear and quantile methods were used to examine the effects of maternal biological (non-modifiable [age, parity, height] and modifiable [pre-pregnant body mass index (BMI) and gestational weight gain (GWG)]), behavioral (smoking), and social (marital status, support partner, Medicaid) factors. Logistic regression demonstrated a positive relationship between LGA and the biological factors parity, height, GWG, and pre-pregnant BMI (which showed highest level of increased risk). Linear regression coefficients showed a significant relationship between birth weight z-scores and all variables except marital status and Medicaid. Quantile regression showed a positive increasing trend of the regression coefficient for pre-pregnant BMI and GWG as the birth weight percentile increased. Increases in the regression coefficient across the percentiles were seen in the significant predictors age and height. Smoking had a negative and reducing impact as birth weight z-scores percentiles increased. Marital status was not identified as a significant predictor; however, it was identified as an interaction term with pre-pregnant BMI. Biological and social factors only contributed to a low level of the explained variance in the ponderal index linear regression model. Parity, pre-pregnant BMI, GWG, gestational age and gender were significant in the linear and quantile regression models. The quantile model showed that the influence of pre-pregnant BMI increased as the ponderal index percentile increased. Pre-pregnant BMI had a higher impact than GWG at all levels. Parity, GWG, gestational age and gender failed to show temporal trends. Results indicate that the mechanisms of influence of the modifiable biological factor pre-pregnant BMI changes as birth weight indices increase. The impact of pre-pregnant BMI is greatest at the higher birth weight indices. With ongoing research suggesting that infants with a high birth weight index are at risk for childhood obesity, increased pre-pregnant BMI may be contributing to long-term health risks for the offspring. Health care providers need to discuss the importance of optimal BMI in women well in advance of conception.