Objective: To examine the (1) normal ranges of anthropometric and insulin resistance/sensitivity indices (homeostatic model assessment for insulin resistance, homeostatic model assessment for insulin sensitivity, and quantitative insulin sensitivity check index) for Iranian pregnant women and their newborns and (2) associations between maternal anthropometric and metabolic values and infants' birth weights among Iranian women.
Methods: Anthropometric and metabolic values of 163 singleton non-diabetic pregnant women in Tehran, Iran (2014) were collected before and during pregnancy and at delivery. Linear regression, multivariable regression, and Student t tests were used to evaluate correlations between birth weight and maternal variables.
Results: Linear regression modeling suggested that maternal serum glucose (p = 0.2777) and age (p = 0.6752) were not associated with birth weight. Meanwhile, maternal weight and body mass index before pregnancy (p = 0.0006 and 0.0204, respectively), weight at delivery (p = 0.0036), maternal height (p = 0.0118), and gestational age (p = 0.0016) were positively associated with birth weight, while serum insulin (p = 0.0300) and homeostatic model assessment for insulin resistance (p = 0.0334) were negatively associated with infant's birth weight. Using multivariate modeling, we identified severalconfounders: parity (multipara mothers delivered heavier babies compared to first-time mothers) explained as much as 24% of variation in birth weight (p = 0.005), maternal height explained 20.7% (p = 0.014), gestational age accounted for 19.7% (p = 0.027), and maternal body mass index explained 19.1% (p = 0.023) of the variation in the infant's birth weight. Maternal serum insulin and infant's sex were not observed to be associated with birth weight (p = 0.342 and 0.669, respectively) in the overall model.
Conclusion: Overweight/obese women may experience higher incidence of delivering larger babies. Multivariable regression analyses showed that maternal body mass index and height, parity, and gestational age are associated with newborn's birth weight.
Keywords: Neonates; birth weight; body mass index; homeostatic model assessment; low/high birth weight; pregnancy.