The relationship between habitual physical activity patterns of pregnant women and foetal growth parameters : a longitudinal study
Van Oort, Andries Fourie
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Regular physical activity during pregnancy provides both maternal and infant health benefits. The complexity of measuring physical activity during pregnancy hampers the determination of the optimal dose of habitual physical activity for pregnant women and has led to broad physical activity guidelines for pregnant women. Subjectively-determined physical activity levels by means of questionnaires may have contributed to these broad guidelines. However the ActiHeart®, a dual heart rate monitor and accelerometer, is an accurate and reliable measurement tool to determine physical activity levels during pregnancy. Maternal physical activity tends to decrease during pregnancy and may lead to various health risks, including excessive weight gain, risk for gestational diabetes, lower back pain and adverse foetal outcomes. Determining the influence of physical activity on foetal growth is confounded by various variables, therefore objectively-measured habitual physical activity is essential. This study aims to objectively determine habitual physical activity patterns of pregnant women and the relationship between habitual physical activity and foetal growth parameters. In a longitudinal, observational, cohort study design, 60 pregnant women were measured at four stages in their pregnancy: the first trimester (9 – 12 weeks), second trimester (20 – 22 weeks), third trimester (28 – 32 weeks) and three months postpartum. Demographic information was collected by means of a questionnaire specifically compiled for this study, followed by anthropometric measurements (height and weight). Assessment of the participants resting blood pressure, heart rate (Microlife® Semi-Automatic blood pressure and heart rate monitor) and metabolic rate (FitmateTM, Cosmed) was obtained. Thereafter, a step-test was performed for individualised calibration of the ActiHeart® device for assessment of habitual physical activity patterns over a 7-day period. Foetal growth parameters that included birth weight (kg), birth length (cm), abdominal circumference (cm) and head circumference (cm), were collected from medical records and from the mother post-partum. Habitual physical activity, presented as average Activity Energy Expenditure (AEE), physical Activity Level (PAL), activity counts and minutes spent in activity, declined from the first to the third trimester of pregnancy. The AEE during the first trimester averaged 803 ± 34 kCal/day and declined statistically significant to 592 ± 383 kCal/day in the third trimester. Minutes spent per week doing moderate activity declined from 103 ± 83 min/week in the first trimester to 55 ± 66 min/week in the third trimester. Average pregnancy AEE indicated a non-significant negative relationship with all foetal growth measurements - birth weight (r = - 0.39, p = 0.45), birth length (r = - 0.16, p = 0.77), Ponderal Index (r = - 0.34, p = 0.51) - and a non-significant positive relationship with head circumference at birth (r = 0.14, p = 0.79). In conclusion, the objectively-determined, habitual physical activity levels of the participants did not meet the stated guidelines for pregnant women. During the progression of pregnancy, the activity levels declined significantly at the third trimester. The habitual activity levels indicate no effect on the foetal growth parameters.