Impact of maternal obesity on resting muscle sympathetic nerve activity during uncomplicated pregnancy: a longitudinal assessment

Maternal obesity increases the risk of adverse pregnancy outcomes. The mechanisms that contribute to this elevated risk are unclear but may be related to greater activity of the sympathetic nervous system, which is associated with hypertensive disorders of pregnancy. We hypothesized that resting muscle sympathetic nerve activity (MSNA) would be greater in women with obesity during pregnancy when compared with normal-weight women. Blood pressure, heart rate, and MSNA were recorded during 5 min of supine rest in 14 normal-weight women [body mass index (BMI) 22.1 ± 2.1 (SD) kg/m²] and 14 women with obesity (BMI 33.9 ± 3.5 kg/m²) during (early and late) pregnancy and postpartum. All women had uncomplicated pregnancies. Resting MSNA burst frequency was not different between groups during early (normal weight 17 ± 10 vs. obesity 22 ± 15 bursts/min, P ¼ 0.35) but was significantly greater in the obesity group during late pregnancy (23 ± 13 vs. 35 ± 15 bursts/min, P ¼ 0.031) and not different postpartum (10 ± 6 vs. 9 ± 7 bursts/min, P ¼ 0.74). These findings were also apparent when comparing burst incidence and total activity. Although still within the normotensive range, systolic blood pressure was greater in the obesity group across all time points (P ¼ 0.002). Diastolic blood pressure was lower during pregnancy compared with postpartum (P < 0.001) and not different between groups (P ¼ 0.488). Heart rate increased throughout pregnancy in both groups (P < 0.001). Our findings suggest that maternal obesity is associated with greater increases in sympathetic activity even during uncomplicated pregnancy. Future research is needed to determine if this is linked with an increased risk of adverse outcomes or is required to maintain homeostasis in pregnancy.