RESUMEN
Systolic time interval measurements were made sequentially during second, third trimesters and postpartum period. Recordings were made in the supine position after bed rest for at least five minutes in order to obtain a steady state. In second trimester, pre-ejection period index (PEPI) was significantly shortened and left ventricular ejection period index(LVETI) remained normal while PEP/LVET decreased. Four possible mechanisms may be involved to account for the alterations in hemodynamic changes during this period(late stage of second trimester) : (1) increased metabolic demands of pregnancy: (2) hemodynamic effects of hypervolemia: (3) circulatory adjustments secondary to an arteriovenous shunt-like effect of the placental circulation: (4) cardiovascular effect of steroid hormone. The third trimester was characterized-by a markedly shortened LVETI, a prolonged PEPI and PEP/LVET. This findings are consistent with impaired left ventricular performance and are probably due to decreased left ventricular preload resulting from diminished venous return secondary to inferior vena caval obstruction by the large gravid uterus. In the postpartum period, the PEPI and PEP/LVET remained elevated and the LVETI shortened in the supine position. It is concluded that alterations in systolic time intervals occur normally during the course of uncomplicated pregnancy and persist into the postpartum period.