Objective: To generate reference ranges for bioelectrical impedance indices throughout pregnancy and to investigate whether a relationship exists between these indices and the neonatal birth weight.
Study design: Pregnant women with a singleton gestation, gestational age lower than 12 weeks, and absence of medical diseases before pregnancy were enrolled. Patients with pregnancy complications, such as hypertensive disorders, diabetes, and antiphospholipides syndrome were excluded. Antrophometric maternal parameters and bioelectrical impedance measurements were performed during the first, second, third trimester of pregnancy, at delivery and 60 days after delivery. Height(2)/resistance (cm(2)/Omega) and height(2)/reactance (cm(2)/Omega) were utilized to estimate the total and extracellular body water amounts, respectively. Spearman rank correlations and cox proportional hazard modelling were used for statistical purposes.
Results: 169 patients completed all measurements. Total and extracellular water amounts significantly increase as pregnancy advances and return to the pre-pregnancy values within 60 days after delivery. After adjustment for gestational age at delivery, fetal sex, and smoking habits, height(2)/resistance at 25 weeks (hazard=1.04, 95% confidence interval (CI) 1.02-1.06, P<0.005), height(2)/resistance at 30 weeks (hazard=1.03, 95% CI 1.01-1.05, P<0.005), height(2)/reactance at 20 weeks (hazard=1.03,95% CI 1.01-1.05, P<0.005), and height(2)/reactance at 25 weeks (hazard=1.03, 95% CI 1.01-1.04, P<0.01) were found to be independent predictors of birth weight.
Conclusion: We have provided reference ranges for bioimpedance analysis during pregnancy, an easy, fast and non invasive method to estimate the body water composition during pregnancy. Bioelectrical impedance indices during the second trimester of pregnancy are independently related to the birth weight.