title: Incidence of placental abruption in relation to cigarette smoking and hypertensive disorders during pregnancy: a meta-analysis of observational studies.
abstract: OBJECTIVE
  To systematically review the literature and summarize the relationship between cigarette smoking and placental abruption, and to evaluate the joint influences of smoking and hypertensive disorders (chronic hypertension and preeclampsia) on the subsequent development of abruption.
  
  
  METHODS
  We reviewed studies identified through a MEDLINE literature search between 1966 and 1997 and through studies cited in the references of published reports.
  
  
  METHODS
  A total of 13 observational (seven case-control and six cohort) studies were identified which included a total of 1,358,083 pregnancies. We excluded case reports on placental abruption, and restricted the literature search to studies published in English. A meta-analysis was performed by computing pooled odds ratios based on random-effects models describing the association between placental abruption, smoking, and hypertensive disorders. Potential sources of heterogeneity among these studies were explored in detail.
  
  
  RESULTS
  The overall incidence of placental abruption was 0.64% (8724 of 1,358,623). Smoking was associated with a 90% increase in the risk of placental abruption (odds ratio [OR] 1.9, 95% confidence interval [CI] 1.8, 2.0). This pattern was consistent by study design (case-control compared with cohort studies) and smoking prevalence (low compared with high prevalence, defined as less than 30% compared with 30% or more, respectively). However, the association was significantly (p < .001) stronger among the seven studies conducted outside the United States (OR 2.1, 95% CI 2.0, 2.2), compared with the six studies conducted in the United States (OR 1.6, 95% CI 1.5, 1.8). Pooled population attributable risk percentage for each stratum ranged between 15% and 25%, implying that 15-25% of placental abruption episodes are attributable to cigarette smoking. Data on the dose-response relationship between number of cigarettes smoked per day and the risk of abruption indicate that the OR increased with increasing number of cigarettes smoked. Furthermore, a meta-analysis of the joint effects of smoking and hypertension during pregnancy on the development of abruption identified two published studies, including 102,609 pregnancies. In the presence of smoking, the risk of abruption was further increased due to chronic hypertension, mild or severe preeclampsia, or chronic hypertension with superimposed preeclampsia.
  
  
  CONCLUSIONS
  Our meta-analyses showed an increased risk for placental abruption in relation to both cigarette smoking and hypertensive disorders during pregnancy. Because cigarette smoking is a modifiable risk factor, and hypertensive disorders are potentially treatable if diagnosed early in pregnancy, patient education, smoking cessation programs, and early prenatal care may be important factors in the prevention of placental abruption.
authors.affiliation: The Center for Perinatal Health Initiatives, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School/St. Peter's Medical Center, New B.
authors.forename: C V
authors.initials: CV
authors.lastname: Ananth
authors.forename: J C
authors.initials: JC
authors.lastname: Smulian
authors.forename: A M
authors.initials: AM
authors.lastname: Vintzileos
mesh_terms: D000037:Abruptio Placentae / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications*; D015994:Incidence; D011225:Pre-Eclampsia / Q000150:complications*; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular; D012907:Smoking / Q000009:adverse effects*