TEMPORAL RELATIONSHIPS BETWEEN HORMONAL AND HEMODYNAMIC-CHANGES IN EARLY HUMAN-PREGNANCY

Background The systemic hemodynamic profile of human pregnancy is char acterized by a decrease in mean arterial pressure, a rise in cardiac o utput and plasma volume in association with an increase in renal plasm a flow and glomerular filtration rate. The factors and the time course responsible for the initial hemodynamic changes seen in human pregnan cy have not been completely documented. We hypothesize that systemic a nd renal hemodynamic changes occur early, prior to the presence of the fetal-placental unit. Methods. Thirteen women were studied prior to a nd immediately following conception in identical fashion at gestationa l weeks 6, 8, 10, 12, 24 and 36. Individuals underwent mean arterial p ressure, cardiac output, inulin and PAH clearance determinations. Resu lts. Mean arterial pressure decreased by six weeks gestation (mid foll icular 81.5 +/- 2.6 vs. six weeks 68.7 +/- 2.0 mm tig, P < 0.001) in a ssociation with a significant increase in cardiac output, a decrease i n systemic vascular resistance and an increase in plasma volume. Renal plasma flow and glomerular filtration tate increased by six weeks ges tation. Plasma renin activity and aldosterone concentration increased significently by six weeks, whereas norepinephrine levels did not chan ge throughout pregnancy. Atrial natriuretic peptide levels increased l ater, at 12 weeks gestation. Plasma cGMP levels decreased and cGMP cle arance increased by six and eight weeks, respectively. Conclusions. Pe ripheral vasodilation occurs early in pregnancy Drier to full placenta tion in association with renal vasodilation and activation of the reni n-angiotensin-aldosterone system. Plasma volume expansion occurs early , followed later by increases in ANP concentration, suggesting that AN P increases in response to changes in intravasular volume.