Comparison of isotope dilution with bioelectrical impedance analysis among HIV-infected and HIV-uninfected pregnant women in Tanzania.

Background: Bioelectrical impedance analysis (BIA) is a simple tool to assess total body water (TBW), from which body composition can be estimated using statistical equations. However, standard BIA equations have not been sufficiently validated during pregnancy, in HIV infection, or in sub-Saharan Africa. We therefore compared TBW estimates from multifrequency BIA with those from the reference method deuterium isotope dilution (Deut) in a cohort of 30 HIV-uninfected and 30 HIV-infected pregnant women from Tanzania.

Methods: We enrolled pregnant women presenting for routine antenatal care and collected data on pregnancy outcomes. At each trimester of gestation and once at 10-wk post-partum, we measured maternal anthropometry, TBW_BIA, and TBW_Deut.

Results: TBW_BIA was highly correlated at each time point with TBW_Deut among HIV-infected (all P ≤0.001) and HIV-uninfected women (all P <0.0001). During pregnancy, mean TBW_BIA progressively underestimated TBW_Deut in the overall cohort; trimester-specific differences (mean ±SD) were -1.02 ±2.36 kg, -1.47 ±2.43 kg, and -2.42 ±2.63 kg, respectively. The difference at 10-wk postpartum was small (-0.24 ±2.07 kg). In Bland-Altman and regression models, TBW_BIA was subject to a systematic predictive bias at each antenatal and postnatal time point (all P ≤0.038). Among HIV-positive women, TBW_Deut measured during the first (P =0.02) and second trimester (P =0.03) was positively related to birthweight.

Conclusions: The validity of current BIA equations to assess TBW during pregnancy and in the postpartum period among women from sub-Saharan Africa remains uncertain. Deuterium dilution may assess aspects of maternal body composition relevant for pregnancy outcomes among HIV-infected women.