American Journal of Epidemiology Advance Access originally published online on May 20, 2008
American Journal of Epidemiology 2008 168(4):422-426; doi:10.1093/aje/kwn115
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ORIGINAL CONTRIBUTIONS |
Effects of Interpregnancy Interval on Blood Pressure in Consecutive Pregnancies
From the Epidemiology Branch, National Institute of Child Health and Human Development, Bethesda, MD
Correspondence to Dr. Jun Zhang, Epidemiology Branch, National Institute of Child Health and Human Development, Building 6100, Room 7B03, Bethesda, MD 20892 (e-mail: zhangj{at}mail.nih.gov).
Received for publication December 18, 2007. Accepted for publication April 4, 2008.
The lower risk of preeclampsia observed in parous women has prompted a hypothesis that cardiovascular adaptation from a first pregnancy has ongoing benefits which contribute to a reduced risk of preeclampsia in the second pregnancy. However, how the interpregnancy interval affects mean arterial pressure (MAP) as an indicator of cardiovascular adaptation in subsequent pregnancies has not been well studied. The authors examined the effect of interpregnancy interval on MAP in consecutive pregnancies using data from the Collaborative Perinatal Project (1959–1965) and a semiparametric random-effects regression model. Prenatal MAP measurements were available for 533 women with both first and second births. MAP was lower in the second pregnancy (by approximately 2 mmHg) for very short interpregnancy intervals. However, this difference diminished when the interval increased, and it totally disappeared for intervals longer than 2 years. The authors conclude that although MAP is lower in the second pregnancy than in the first pregnancy, the effect persists for only a short time. It is therefore unlikely that mechanisms involving MAP as an indicator of cardiovascular adaptation contribute appreciably to the reduced risk of preeclampsia in subsequent pregnancies. However, it does not rule out the possibility that other mechanisms of cardiovascular adaptation persist longer.
birth intervals; blood pressure; pre-eclampsia; pregnancy
Abbreviations: CPP, Collaborative Perinatal Project; MAP, mean arterial pressure