The effect of obesity and position on heart rate in pregnancy

Abstract

Objective: To determine the prevalence of resting sinus tachycardia among pregnant women during routine third-trimester antenatal visits, and to determine the relationship between body mass index(BMI) and heart rate.Methods: In this cross-sectional study, pregnant women at 32-40 weeks' gestation were evaluated at routine antenatal visits between September 1996 and August 1997. Patientswith medical disorders were excluded. Height, weight and pulse in both the sitting and the left lateral recumbent position were obtained. BMI was based on current weight, and those with a BMI of ≥ 30kg/m2 were classified as obese. Sinus tachycardia was defined as a heart rate of ≥ 100 beats/min.Results: The prevalence of tachycardia was 39% (n = 93) when seated, and29% on the left side. The corresponding rates of sinus tachycardia when seated for obese (n = 31) and non-obese (n = 62) pregnant women were 58% and 29% (relative risk 2.0, 95% confidenceinterval 1.2, 3.3). However, the rates of tachycardia on the left side were not significantly different: 32% for obese and 27% for non-obese (relative risk 1.2, 95% confidence interval 0.6, 2.3).Conclusion:Resting tachycardia during routine antenatal visits may be more common than was previously recognized, and the majority of obese pregnant women are tachycardic when seated. When obese women are tachycardicin the seated position their heart rate should be reassessed after 5 min in the left lateral recumbent position.