EARLY-PREGNANCY CHANGES IN HEMODYNAMICS AND VOLUME HOMEOSTASIS ARE CONSECUTIVE ADJUSTMENTS TRIGGERED BY A PRIMARY FALL IN SYSTEMIC VASCULARTONE

OBJECTIVE: The purpose of this study was to test the hypothesis that e arly pregnancy changes in volume homeostasis develop as a consequence of preceding changes in maternal hemodynamics. STUDY DESIGN: Maternal cardiovascular function of 10 pregnant women was followed up by Dopple r echocardiography. Vascular filling state and volume homeostasis were evaluated by echocardiographic index values, glomerular filtration ra te, serum osmolality, and volume-regulating hormones. Studies were per formed weekly in early pregnancy, in the second and third trimesters, and post partum. Changes relative to the fifth week and the consistenc y of changes between weeks 5 and 8 were evaluated by nonparametric sta tistics. RESULTS: In early pregnancy cardiac output increased and afte rload decreased. Concomitant increases in ultrasonic preload index val ues and glomerular filtration rate were accompanied by decreases in se rum renin, Na+, and osmolality. CONCLUSION: These data support the con cept that maternal hemodynamic adaptation to pregnancy is most likely triggered by a primary fall in systemic vascular tone. The resulting r apid fall in preload and afterload leads to a compensatory increase in heart rate and activation of the volume-restoring mechanisms. Subsequ ently cardiac output increases because of a rise in stroke volume, whi ch develops because the vascular filling state normalizes, whereas the reduced afterload reduction is maintained.