Measuring Energy Expenditure in Habitually Active and Sedentary Pregnant Women

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Abstract
To describe patterns of energy expenditure (EE) during pregnancy and to assess the convergent validity of three methods of estimating EE. We administered heart rate (HR) telemetry, accelerometry, and a physical activity record (PAR) over two consecutive days at weeks 20 and 32 of pregnancy and 12 wk postpartum to 28 habitually active and 28 habitually sedentary women. Mean daily waking-time EE at 20 wk by HR telemetry was 1814 (SD 443) kcal in active women and 1738 (448) kcal in sedentary women (P > 0.50), and did not change over the period of study (for active women P > 0.40; for sedentary women P > 0.70). Compared with HR telemetry, accelerometry underestimated EE by approximately 400 kcal x d-1, and the PAR overestimated EE by a similar amount, at all time periods in both active and sedentary women. EE, expressed per unit body weight, was consistently higher for active than for sedentary women during pregnancy. Pairwise correlations between methods ranged from 0.37 to 0.90 across time periods in both active and sedentary women. Correlations were lower (range 0.07-0.81) when adjusted for the length of the recording day. All methods were sensitive to variation in both the rate of EE and the duration over which activity was monitored. Accelerometry and PAR are useful methods for categorizing EE in epidemiologic studies among pregnant women but absolute estimates are biased relative to HR.