Preeclampsia and maladaptation to pregnancy: a role for atrial natriuretic peptide?

Background: The majority of women with a history of preeclampsia have either an underlying thrombophilic disorder or a vascular disorder. In this study, we tested the hypothesis that only the latter condition predisposes for abnormal hemodynamic adaptation to pregnancy.
Methods: Thirty-seven formerly preeclamptic subjects were subdivided into a hypertensive (HYPERT, N = 10), a normotensive thrombophilic (THROMB, N = 13) and a normotensive nonthrombophilic subgroup (NONTHROMB, N = 14). In these women and in 10 normal parous controls, the following variables were measured at least five-months postpartum at day 5 (+/-2) of the menstrual cycle and again at five- and seven-weeks amenorrhea in the next pregnancy: mean arterial pressure, heart rate, cardiac output, central cardiovascular dimensions, plasma volume, glomerular filtration rate, effective renal plasma flow, 17-beta estradiol, progesterone, the hormones of the renin-angiotensin-aldosterone (RAAS) axis, catecholamines and alpha-atrial natriuretic peptide.
Results: The early pregnancy rise in cardiac output, renal variables, RAAS activity, and plasma volume was comparable in all groups. However, the HYPERT and NONTHROMB subgroups differed from controls by a lower plasma volume in the prepregnant state. In addition, only the women in these two subgroups responded to pregnancy by a rise in circulating alpha-atrial natriuretic peptide. In addition, at seven weeks, in the subjects belonging to the HYPERT and NONTHROMB subgroups, plasma volume was the lowest and correlated inversely with the concomitant circulating level of alpha-atrial natriuretic peptide.
Conclusion: The hemodynamic adaptation to pregnancy in the HYPERT and NONTHROMB subgroups differs from that in THROMB and controls by an early pregnancy rise in alpha-atrial natriuretic peptide. As a consequence, the early pregnancy plasma volume expansion in the NONTHROMB and HYPERT subgroups is less than in normal parous controls.