Evaluating the effect of preeclampsia and time interval on subsequent pregnancies blood pressure
Howe, Lindsay Spencer
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INTRODUCTION Preeclampsia, a hypertensive disorder of pregnancy, affects 3% to 7% of women throughout the world. Preeclampsia is a leading cause of maternal and infant mortality worldwide, occurring primarily in nulliparous women. Despite extensive research over the past decade, the underlying pathophysiological mechanisms of the disease are largely unknown. A recent hypothesis has suggested that when a pregnancy is complicated by preeclampsia, it is the result of an inability of the maternal cardiovascular system to fully adapt to the physiologic challenge of pregnancy. This may result when there is an underlying and predisposing prepregnancy maternal cardiovascular state that leads to the pathophysiologic consequences of preeclampsia when pregnancy is superimposed. Despite evidence for familial predisposition and presumed multifactorial genetic inheritance, preeclampsia generally occurs in first pregnancies and does not recur when the interpregnancy interval is short. One explanation for these observations is that pregnancy itself modifies the maternal cardiovascular system in ways that persist postpartum and reduce the risk for preeclampsia recurrence, at least for a limited period of time. It has been demonstrated that the maternal cardiovascular system is remodeled during pregnancy, and these changes extend postpartum. The long lasting reduction in mean arterial pressure postpartum that pregnancy induces, and the cardiovascular remodeling that accounts for this, may allow for easier adaptation to volume expansion in subsequent pregnancies, even when the first pregnancy was complicated by preeclampsia. As the maternal cardiovascular system returns, over time, to the baseline condition, this protective effect diminishes. With this knowledge, we hypothesize that the length of time between pregnancies is negatively correlated to the likelihood of recurrence of preeclampsia, and more narrowly that the length of time between pregnancies is inversely associated with mean arterial pressure differences comparing pregnancies across all trimesters. METHODS This study was a retrospective chart review of existing medical records. We reviewed medical records of women who had been diagnosed with preeclampsia at Fletcher Allen Health Care, during their first advanced pregnancy between 1995 and 2014, who went on to have a subsequent pregnancy within that time period. We aimed to identify factors that could affect the blood pressure and risk of preeclampsia in women who were previously diagnosed, including previous medical history and demographic variables. We collected blood pressures from each pregnancy, across each trimester, marking the recurrence of preeclampsia and other complications. Mean antepartum mean arterial blood pressure, pulse pressure, and systolic and diastolic blood pressures were calculated and compared between pregnancies examining differences as a function of interpregnancy interval. RESULTS One hundred and seventy two subjects were identified for review. Overall, there was evidence of a significant association of interpregnancy interval (IPI) and the difference in mean arterial pressure (MAP) between pregnancies (p=0.04). The mean MAP of pregnancy decreased significantly between first and second pregnancies when the interpregnancy interval was <24 months (p=0.0018) and 24-48 months (p=0.0003), but the change was non-significant at interpregnancy intervals of >48 months (p=0.55). The mean MAP during the third trimester, specifically, decreased significantly between first and second pregnancies across all subject groups (IPI <24 months: p<0.0001; IPI 24-48 months: p<0.0001; IPI >48 months: p=0.03). Preeclampsia recurred in 39 of the second pregnancies. The recurrence rate of preeclampsia did not vary significantly with interpregnancy interval (p=0.21). DISCUSSION/CONCLUSIONS The interval between preeclamptic pregnancies and subsequent pregnancies has an influence on the MAP of the second pregnancy. There is good evidence of a temporal influence, in that the shorter interpregnancy intervals resulted in a greater reduction in MAP when compared to the longer interpregnancy interval. We believe that with additional research on interpregnancy intervals >48 months, there could be more a conclusive association identified between the rate of recurrence of preeclampsia and the length of interpregnancy interval.