Background: It has been suggested that maternal vascular adaptations during pregnancy differ between nulliparous and multiparous women. Therefore, we examined the associations of parity with blood pressure and hemodynamic placental function during pregnancy and risks of gestational hypertensive disorders.
Methods: The study was embedded in a population-based prospective cohort study among 8,377 pregnant women. Information about parity and gravidity was obtained at enrollment. Blood pressure was repeatedly measured in each trimester and mean pulsatility and resistance indexes of uterine artery were measured in second and third trimesters. Information on gestational hypertension and preeclampsia was available from medical records.
Results: As compared with nulliparous women, multiparous women had a lower systolic and diastolic blood pressure in each trimester of pregnancy and a slightly higher second and third trimester uterine artery resistance and pulsatility indexes (all P values < 0.05), but a lower risk of third trimester uterine artery notching (odds ratio (OR) 0.67 (95% confidence interval (CI):0.53, 0.84)). The risks of gestational hypertension and preeclampsia were lower among multiparous women as compared with nulliparous women (OR 0.32 (95% CI: 0.24, 0.43) and OR 0.24 (95% CI: 0.16, 0.37), respectively). Among multiparous women only, we did not observe associations of parity with hemodynamic parameters.
Conclusions: Nulliparous pregnant women have higher blood pressure levels throughout pregnancy and higher risks of notching and gestational hypertensive disorders. The first pregnancy might be a major risk factor for maternal hemodynamic maladaptations and vascular complications. Further studies are needed to explore the underlying mechanisms and consequences for fetal growth and development.