Maternal body composition at term gestation and birth weight: is there a link?

To assess the relative influence of maternal body composition at late gestation on birth weight, we examined maternal body composition near term (36.50 +/- 2.67 weeks gestation) in a group of 29 women, aged 20-39 years. The women came to the laboratory after an overnight fast. After anthropometric measurements, bioelectrical impedance analysis (BIA) was performed, determining resistance (R) and reactance (Xc), with a Tefal scale at 50 kHz. Fat mass (FM, kg) and fat-free mass (FFM, kg) were determined with the total body water (TBW) equation of Siri. The correlation between BIA parameters and birth weights was examined by linear regression analysis. All subjects delivered between 37 and 41 weeks' gestation. The mean +/- SD values of the studied parameters were: Xc=490.00 +/- 77.34 Omega, R=55.71 +/- 8.71 Omega, FM=24.18 +/- 6.51 kg, FFM=45.82 +/- 2.65 kg, maternal weight gain=9.51 +/- 6.43 kg, birth weight=3.43 +/- 0.36 kg. A direct significant correlation was found between FFM, maternal weight gain, and birth weight. It is known that in late pregnancy, maternal weight gain over gestation is linked to birth weight. We observed that FFM was the most important maternal body component associated with the newborn weight at term gestation, and we believe that this finding might be elucidated by fluid retention. In fact, resistance seemed to be inversely related to birth weight and we do not overlook the link between resistance and TBW. The implementation of our study could shed more light on the influence of maternal body composition on birth weight.