The influence of pregnancy on arterial compliance

To examine the effect of pregnancy and the interval between pregnancies on arterial compliance as measured by mean arterial pressure (MAP) and pulse pressure.

We conducted a 3-month chart review of deliveries at a tertiary care hospital (index pregnancies). Data collected included demographics, obstetric history, blood pressures, prepregnancy weight, weight gain, and neonatal outcome. If a subject's first delivery occurred at our institution, these records were reviewed in a similar fashion. Mean antepartum MAP and pulse pressure were calculated and compared for each trimester between index and first pregnancies. Statistical methods employed included repeated measures analysis of variance, repeated measures analysis of covariance, and correlation analysis.

Two hundred eighty-five charts were reviewed. Forty-seven women had complete data covering both index and first pregnancy. Mean arterial pressure was significantly higher in all trimesters of first compared with index pregnancies (first pregnancy-first trimester 82.0 +/- 8.1 mm Hg, index pregnancy-first trimester 79.4 +/- 7.6 mm Hg, P = .032; first-second trimester 81.6 +/- 6.7 mm Hg, index-second trimester 78.7 +/- 6.6 mm Hg, P = .016; first-third trimester 83.9 +/- 6.9 mm Hg, index-third trimester 81.6 +/- 6.9 mm Hg, P = .047). Repeated measures analysis of covariance confirmed that pregnancy order contributed independently to differences in MAP. The interval between pregnancies was found to be inversely related to the difference in MAP from first to index pregnancies by trimester (r = -0.41, P = .004) and the change in MAP within pregnancy from first to third trimester (r = -0.31, P = .046).

Mean arterial pressure is reduced in subsequent pregnancies compared with first pregnancies. This raises the possibility that pregnancy plays a role in modifying cardiovascular compliance. Consistent with this, the effect has temporal limitations in that the shorter the interval between pregnancies, the greater the reduction in MAP.