Effect of Parity on Cardiovagal Baroreflex Sensitivity and Blood Pressure Variability in Sequential Pregnancies and Postpartum

Abstract

BackgroundPregnancy is characterized by significant maternal cardiovascular adaptations, mediated in part though autonomic control mechanisms, that differ by parity (number of prior pregnancies ≥20 weeks). Pregnancy‐related cardiovascular changes are more pronounced in parous women compared with women in their first pregnancy, and sympathetic hyperactivity characteristic of late gestation is exaggerated in subsequent compared with prior pregnancy. The long‐term impact of repeated pregnancy‐related adaptations on maternal cardiovascular function is unknown, but may underlie the association between multiparity and elevated cardiovascular disease risk. The objectives of this study were to assess cardiovagal baroreflex sensitivity (BRS) and beat‐by‐beat blood pressure variability (BPV) across gestation and postpartum in consecutive pregnancies to characterize effects of parity on cardiovascular function in young women. We hypothesized that BRS would be blunted and BPV augmented in subsequent pregnancies and this would persist postpartum.MethodsAll women had singleton term pregnancies without undergoing fertility treatment and were free from history of chronic hypertension, diabetes or hypertensive pregnancy disorder. Longitudinal assessments were conducted in the first (T1, 12±2 wks), second (T2, 22±2) and third trimester (T3, 32±3) and early postpartum (10±2 weeks) in a prospective pregnancy cohort. Seven women were enrolled for two consecutive pregnancies (inter‐pregnancy interval 1.0‐1.5 yrs, body mass index Δ = 0.3 kg/m2, P=0.31). Women with one study pregnancy were grouped by current parity: first pregnancy (Preg1, N=45, 29±4 years of age), second (Preg2, N=57, 30±4 yrs) and third‐fifth (Preg3, N=41, 32±4 yrs). BRS and BPV were measured for 10 minutes by finger plethysmography and electrocardiography. BRS was calculated via the sequence technique (ms/mmHg) and BPV by standard deviation (mmHg).ResultsIn consecutive pregnancies, BRS was lower in the second studied pregnancy compared with the first (T1 median Δ = ‐4.1 ms/mmHg, P=0.03; T2 Δ = ‐3.2, P=0.02; T3 Δ = ‐0.6, P=0.06) and postpartum (Δ = ‐3.7, P=0.06). BPV was higher in the second compared with first pregnancy in early‐mid gestation (systolic, T1 median Δ = 0.4 mmHg, P=0.03; T2 Δ = 1.4, P=0.046; T3 Δ = 1.2, P=0.16) but not postpartum (Δ = 1.0, P=0.16). In the women with one study pregnancy, body mass index in T1 did not differ by parity group (P=0.21). Women in Preg3 had lower BRS compared with women in Preg1 or Preg2 in T1, T2 and postpartum independent of age (parity main effect: F(2, 496)=8.3, P<0.001; time*parity interaction, P=0.56). BPV was higher after Preg3 compared with Preg1 and Preg 2 groups postpartum (x̅=1.1 mmHg, adj P=0.04).ConclusionsAcross sequential pregnancies, BRS is blunted and BPV elevated throughout gestation and postpartum in the latter pregnancy. These findings are further supported by blunted BRS in women during and after the ≥third pregnancy compared with a first or second pregnancy, accompanied by a postpartum elevation in beat‐to‐beat BPV. These data indicate that autonomic regulatory mechanisms may be affected by repeated pregnancy and this persists postpartum.