Hormonal influences on cardiovascular function in early pregnancy

To test the hypothesis that cardiovascular adaptations to human pregnancy b egin in the first 4 weeks post ovulation (PO) we obtained estimates of rest ing heart rate (HR), blood pressure (BP), stroke volume (SV), cardiac outpu t (CO), peripheral resistance (TPR), and venous capacity (VC) and complianc e (VCom) weekly under standard conditions beginning on day 3 of the menstru al cycle. The data obtained in cycles with conception were compared to thos e in which conception did not occur. Techniques utilized included EKG, auto mated blood pressure measurement (Dynamap), echocardiography, and plethysmo graphy. No directional changes were observed in any parameter during the cy cles in which conception did not occur. However, in cycles in which concept ion occurred HR increased 10 bpm within 1 week PO and remained at that leve l for the next 7 weeks. BP did not fall significantly until the 5th week PO , SV rose significantly between the 2nd and 3rd week PO and plateaued 10% a bove pre ovulatory levels thereafter. As a result, CO rose and TPR fell sig nificantly within 1 week PO and plateaued 1.5 l/min above and 300 dyne/cm/s (-5) below pre ovulatory levels by the 3rd PO week. VC increased and follow ed a similar time course. These changes were associated with rapid increase s in human chorionic gonadotropin, a fourfold increase in estradiol, and a twofold increase in progesterone. We conclude that the hypothesis is correc t and speculate that the cardiovascular changes are initiated by the rapidl y changing hormonal milieu.