Cardiovascular function in pregnancy: effects of posture

Objective To evaluate the cardiovascular response to active postural change s in pregnancy. Design Prospective study. Setting Outpatient Clinic, Fetal Maternity Unit. Participants Sixteen healthy women referred prior to pregnancy. Methods Heart rate, arterial pressure, echocardiographic end-diastolic and end-systolic left ventricular volumes (Teichholz's formula) were measured i n the three months before pregnancy, at the end of the first and second tri mester. at mid third trimester, and six months after delivery in the supine and standing position, in thirteen women (mean age 33, range 25-38 years). Results Cardiac output (supine position) significantly increased (28%). it reached its maximum at the second trimester, remained steadily elevated in the mid third trimester, and returned to baseline after delivery. Cardiac o utput increased during pregnancy also in the active orthostatic position, t he percentage increase being greater (70%) since the standing pre-conceptio n value was lower. The postural stress induced similar changes in heart rat e, arterial pressure and left ventricular ejection fraction before, during and after pregnancy. However, the reduction in cardiac output associated wi th early standing attenuated significantly at the second trimester and it w as absent at mid third trimester (F = 3.13, P = 0.021). This was due to the interplay between the significantly lesser increase in systemic vascular r esistance, occurring since the first trimester, and the significantly lesse r decrease in left ventricular end-diastolic volume which was observed in t he mid third trimester. Conclusion These data indicate that the elevated cardiac output is adequate ly maintained in pregnancy during the postural challenge, due to optimisati on of the responses of preload and afterload.