Abstract
Properties of bioelectrical impedance analysis (BIA) reflect body-composition and may serve as stand-alone indicators of maternal health. Despite these potential roles, BIA properties during pregnancy and lactation in rural South Asian women have not been described previously, although pregnancy and infant health outcomes are often compromised. This paper reports the BIA properties among a large sample of pregnant and postpartum women of rural Bangladesh, aged 12-46 years, participating in a substudy of a community-based, placebo-controlled trial of vitamin A or beta-carotene supplementation. Anthropometry and single frequency (50 kHz) BIA were assessed in 1,435 women during the first trimester (< or =12 weeks gestation), in 1237 women during the third trimester (32-36 weeks gestation), and in 1,141 women at 12-18 weeks postpartum. Resistance and reactance were recorded, and impedance and phase angle were calculated. Data were examined cross-sectionally to maximize sample-size at each timepoint, and the factors relating to BIA properties were explored. Women were typically young, primiparous and lacking formal education (22.2 +/- 6.3 years old, 42.2% primiparous, and 39.7% unschooled among the first trimester participants). Weight (kg), resistance (omega), and reactance (omega) were 42.1 +/- 5.7, 688 +/- 77, and 73 +/- 12 in the first trimester; 47.7 +/- 5.9, 646 +/- 77, and 64 +/- 12 in the third trimester; and 42.7 +/- 5.6, 699 +/- 79, and 72 +/- 12 postpartum respectively. Resistance declined with age and increased with body mass index. Resistance was higher than that observed in other, non-Asian pregnant populations, likely reflecting considerably smaller body-volume among Bangladeshi women. Resistance and reactance decreased in advanced stage of pregnancy as the rate of gain in weight increased, returning to the first trimester values by the three months postpartum. Normative distributions of BIA properties are presented for rural Bangladeshi women across a reproductive cycle that may be related to pregnancy outcomes and ultimately be used for assessing body-composition in this population.
Highlights
Bioelectrical impedance analysis (BIA) is widely used in evaluating body-composition in epidemiological studies and clinical settings [1,2,3,4], usually by applying measures of resistance or impedance to population-specific, predictive equations for estimating total body-water (TBW), fat-free mass (FFM), and fat mass
The differences in crosssectional BIA variable distributions were not tested across time-points due to lack of independence, distributions of paired differences between the first and the third trimester, and the first or the third trimester and three months postpartum measures were tested against a null hypothesis of no change over time by analysis of variance (ANOVA) and paired t-test where longitudinal data were available
After exclusions (e.g. BIA measurement not taken within timeframe for inclusion in the first or the third trimester or three months postpartum definitions) and losses to follow-up, 1,435, 1,237, and 1,141 women contributed data on BIA properties at the first trimester, third trimester, and three months postpartum respectively, for cross-sectional analyses at these times
Summary
Bioelectrical impedance analysis (BIA) is widely used in evaluating body-composition in epidemiological studies and clinical settings [1,2,3,4], usually by applying measures of resistance or impedance to population-specific, predictive equations for estimating total body-water (TBW), fat-free mass. Even fewer data are available describing BIA properties during pregnancy or lactation in any South Asian populations, possibly due to uncertainty of the value of BIA in assessing the Distribution of bioelectrical impedance properties among rural pregnant women health or nutritional status in the absence of population-specific equations for body-composition [14]. BIA data obtained in large population studies could improve the understanding of the public-health use of BIA, especially where predictive equations based on sophisticated methods of body-composition measurement are unavailable. The present study was designed to generate and compare normative cross-sectional distributions of bioelectrical impedance properties in early pregnancy, late pregnancy, and at three months postpartum in a cohort of women with viable pregnancies or live infants at the time of analysis in a typical rural setting in northern Bangladesh
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