Association of maternal nocturnal heart rate and adverse pregnancy outcomes

Prior data suggest that higher nocturnal heart rate may represent a marker of cardiometabolic disease risk in nonpregnant adults. Data on nocturnal heart rate and pregnancy outcomes are limited. We sought to assess the association of maternal nocturnal heart rate with adverse pregnancy outcomes.

This is a secondary analysis of nulliparas in a prospective cohort at eight US sites undergoing a home sleep study using the Embletta-Gold device with bipolar electrocardiogram at baseline (6⁰-15⁶ weeks) and follow-up (22⁰-31⁶ weeks) visits. Exposures were mean, minimum, and maximum nocturnal heart rate at baseline and follow-up (analyzed separately). Outcomes of interest were gestational diabetes, hypertensive disorders of pregnancy, preterm birth, small-for-gestational age, and stillbirth. Multivariable logistic regression models estimated the odds of each outcome, except for stillbirth due to low frequency, per each 5-beat higher nocturnal heart rate, adjusted for possible confounders.

Among 2952 eligible nulliparas, 30% experienced an adverse pregnancy outcome. We identified higher adjusted odds of gestational diabetes (minimum nocturnal heart rate mean ± standard deviation, gestational diabetes vs. no gestational diabetes: 49 ± 10 vs. 46 ± 11; adjusted odds ratio [aOR] 1.15, 95% confidence interval [CI] 1.03-1.29) and hypertensive disorders of pregnancy (48 ± 11 vs. 46 ± 11; aOR 1.05, 95% CI 1.01-1.10) for each 5-beat higher minimum nocturnal heart rate at baseline; adjusted odds of gestational diabetes were also higher at baseline and follow-up for mean and maximum nocturnal heart rate. At follow-up, we identified lower adjusted odds of small-for-gestational age for each 5-beat higher mean (76 ± 10 vs. 78 ± 9; aOR 0.83, 95% CI 0.78-0.88) and minimum nocturnal heart rate (48 ± 12 vs. 51 ± 13; aOR 0.90, 95% CI 0.86-0.94).

Higher mean, minimum, and/or maximum nocturnal heart rate in pregnancy were associated with higher odds of hypertensive disorders of pregnancy and gestational diabetes. This may reflect higher sympathetic and/or decreased parasympathetic activity in affected gravidas. Conversely, lower mean and minimum nocturnal heart rate in late pregnancy were associated with higher odds of small-for-gestational age, which may be reflective of maladaptive hemodynamic changes in affected gravidas.