Estimates of body water compartments with use of bioelectrical impedance analysis

St Luke's–Roosevelt Hospital Center, Obestity Research Center, Weight Control Unit, 1090 Amsterdam Avenue, New York, NY 10025

Dear Sir:

I read with interest the article published recently in the Journal on bioelectrical impedance analysis (BIA) in women with a normal and hypertensive pregnancy (1). The authors suggested that BIA "can be used to monitor variations in body water compartments in normal pregnancy." Although this is an interesting and potentially important study, the authors should clarify several points for readers. Because BIA was not compared with a reference method, on what basis did the authors conclude that their quantitation of water spaces was valid? This question arises because total body water decreased by 20 L over the course of pregnancy in the subjects who developed gestational hypertension, including a loss of more than one-half of their intracellular water compartment. This information is provided in both Table 2 and Figure 2. An immediate question is whether body weight changes supported the BIA-detected anomalous changes in fluid balance; no body mass data were reported. With only 17.5 L of tissue water during the third trimester, the women with gestational hypertension either lost a substantial portion of their body mass or had severe dehydration. Alternatively, the BIA fluid estimates were inaccurate. Supportive data are provided in Figure 1 expressed as the bioimpedance index, but this index was not defined in the text and the unit, m²/, seems improbable on the basis of the magnitude of the plotted data.

REFERENCE

1. Valensise H, Andreoli A, Lello S, Magnani F, Romanini C, De Lorenzo A. Multifrequency bioelectrical impedance analysis in women with a normal and hypertensive pregnancy. Am J Clin Nutr 2000;72:780–3.