Reproductive hormones and blood pressure during pregnancy.

The mechanisms involved in cardiovasular changes during human pregnancy and the complicated aetiology of gestational hypertension are unclear. Reproductive hormones have known effects on the cardiovascular system in the non-pregnant state and in animal systems, but their effects in human pregnancy are uncertain. In this study of pregnant women, the effects of serum concentrations of relaxin, progesterone and oestradiol on arterial blood pressure were studied. Higher serum concentrations of progesterone and relaxin, but not oestradiol, in early pregnancy were related to lower mean systolic blood pressures in the second and third trimesters. No relationship was found between hormonal concentrations and diastolic blood pressures. However, women with a diastolic blood pressure of >90 mmHg in late pregnancy showed statistically significant lower relaxin concentrations in early pregnancy in comparison with women whose diastolic blood pressure was </=90 mmHg. In a multivariate analysis, the mean systolic blood pressure (P: < 0.0001) and serum relaxin (P: < 0.01) in early pregnancy, but not progesterone, were independently related to systolic blood pressure in late pregnancy. The results support previous experimental and clinical studies. The effect of relaxin may be explained by a possible vasodilatatory action seen in animal studies and appears to be moderate.