Reply to C Nunez

¹ Department of Obstetrics and Gynecology, University of Tor Vergata, Rome, Italy
² Human Nutrition Unit, University of Tor Vergata, Rome, Italy, E-mail: delorenzo{at}uniroma2.it

Dear Sir:

We indeed were interested in determining whether multifrequency bioelectrical impedance analysis (MF-BIA) could be used as a simple method for understanding the evolution of pregnancy by differentiating normal and hypertensive patients. We intended to use this method mostly in a qualitative rather than a quantitative way. For this reason, we were excited to find differences during the evolution of pregnancy in untreated patients. The absolute values of total body water, intracellular water, and extracellular water that we reported were used only for the purpose of discriminating between hypertensive and nonhypertensive patients. We did not intend for MF-BIA to be used as the final body-composition method in this investigation.

Several issues need to be clarified before we can correctly identify exact body composition during pregnancy. For example, parity, dietary intake, fluid intake, daily exercise, fetal weight, fetal amniotic fluid, placental weight, and blood volume expansion are among the factors that must be taken into consideration before we can make any final conclusions regarding body-composition changes during pregnancy.

Gestational hypertension is usually associated with hypovolemia, reduced blood volume, hemoconcentration, elevated hematocrit value, reduced fetal growth, and oligohydramnios, and these features fit with the data obtained in our study. Nevertheless, in term pregnancies, hypertension might appear in patients with pretibial edema, increased body weight, hydramnios, and fetal macrosomia, and these findings are far from the data we collected.

These major differences must be kept in mind and could help the reader in understanding our results. We focused our attention on a select group of patients enrolled in a longitudinal study and evaluated them before any pharmacologic treatment. Special consideration was given to recording qualitative differences between the hypertensive patients and the nonhypertensive patients matched for gestational age, rather than calculating the absolute value of water. The validity of the BIA method for estimating body fluid compartments is supported by numerous publications in the literature with and without accompanying reference methods (1–3).

Last, the units for the BIA index in Figure 1 should be cm² instead of m²; we apologize for this error.

_REFERENCES

1. De Lorenzo A, Andreoli A, Matthie J, Withers P. Predicting body cell mass with bioimpedance by using theoretical methods: a technological review. J Appl Physiol 1997;82:1542–58.
2. Van Loan MD, Lori EK, King JC, Wong WW, Mayclin PL. Fluid changes during pregnancy: use of bioimpedance spectroscopy. J Appl Physiol 1995;78:1037–42.
3. Lukaski HC, Siders WA, Nielsen EJ, Hall CB. Total body water in pregnancy: assessment by using bioelectrical impedance. Am J Clin Nutr 1994;59:578–85.