Objective: To conduct a meta-analysis of published studies on placental abruption to examine its incidence, recurrence, and association with hypertensive disorders (chronic hypertension and preeclampsia) and prolonged rupture of membranes (PROM) in pregnancy.
Data sources: We reviewed studies on placental abruption published since 1950, based on a comprehensive literature search using MEDLINE, and by identifying studies cited in the references of published reports.
Methods of study selection: We identified 54 studies, excluding case reports on placental abruption and studies relating to placenta previa and vaginal bleeding of unknown origin. We also restricted the search to articles published in English.
Tabulation, integration, and results: Studies chosen for the meta-analysis were categorized based on their study design (case-control or cohort), where they were conducted (United States or other countries), source of the data (vital records versus other sources), and magnitude of risk (risk of abruption greater or less than 1.0%). We used both fixed- and random-effects analysis to identify sources of heterogeneity in results among studies. There were striking differences in the incidence of placental abruption between cohort (0.69%) and case-control (0.35%) studies. United States-based studies found a somewhat higher incidence both for cohort (0.81%) and case-control (0.37%) studies compared with studies conducted outside the U.S. (0.60% and 0.26%, respectively). Abruption was more than ten times more common in pregnancies preceded by a pregnancy with abruption. Chronically hypertensive patients were more than three times as likely to develop placental abruption (odds ratio [OR] 3.13, 95% confidence interval [CI] 2.04-4.80) as normotensive patients. The OR for placental abruption was 1.73 (95% CI 1.47-2.04) for patients with preeclampsia. Similarly, women with pregnancies complicated by PROM were more than three times as likely to develop placental abruption (OR 3.05, 95% CI 2.16-4.32). United States-based studies, case-control studies, and studies with an incidence of abruption greater than 1% demonstrated stronger associations between abruption and hypertension and PROM.
Conclusion: Risk of abruption is strongly associated with chronic hypertension, PROM, and especially abruption in a prior pregnancy, and somewhat more modestly with preeclampsia. The criteria for the diagnosis of placental abruption, hypertensive disorders, and PROM may have introduced variability among the results of these studies. More standardized definitions of these pregnancy complications would improve the comparability of the study results.