title: Maternal pre-gravid body weight and risk for placental abruption among twin pregnancies.
abstract: OBJECTIVE
  Placental abruption is a major cause of fetal and neonatal death and has been reported more frequently in twin pregnancies than among singleton gestations. The purpose of this article is to investigate the role of maternal pre-gravid body mass index (BMI) on the risk for placental abruption among twin pregnancies.
  
  
  METHODS
  We used the Missouri maternally linked cohort files (years 1989-1997) consisting of twin live births (gestational age 20-44 weeks). Maternal pre-gravid weight was classified based on the following BMI-based categories: normal (18.5-24.9), underweight (<18.5), overweight (25-29.9), and obese (>30). We used logistic regression for generated adjusted odds ratios with correction for the presence of intra-cluster correlation using generalized estimating equations.
  
  
  RESULTS
  Overall, 261 cases of placental abruption were registered over the entire study period, yielding a placental abruption rate of 14.9/1000. The frequency of placental abruption correlated negatively with maternal BMI in a dose-effect pattern: underweight (19.3/1000); normal weight (16.1/1000); overweight (13.9/1000); and obese (9.5/1000) mothers (p for trend < 0.01). After adjusting for confounders, the likelihood of placental abruption was still lower in obese women (OR = 0.58; 95% CI = 0.38-0.87). By contrast, women who were underweight had a 20-30% greater likelihood for placental abruption when compared with normal weight mothers, although these findings were statistically not significant.
  
  
  CONCLUSIONS
  There is an inverse relationship between pre-gravid maternal BMI and placental abruption. The mechanism by which obesity impacts the likelihood of placental abruption in twin pregnancies requires further study.
authors.affiliation: Division of Preventive, Occupational and Aerospace Medicine, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Muktar H
authors.initials: MH
authors.lastname: Aliyu
authors.forename: Amina P
authors.initials: AP
authors.lastname: Alio
authors.forename: O'Neil
authors.initials: O
authors.lastname: Lynch
authors.forename: Alfred
authors.initials: A
authors.lastname: Mbah
authors.forename: Hamisu M
authors.initials: HM
authors.lastname: Salihu
mesh_terms: D000037:Abruptio Placentae / Q000453:epidemiology*; D000328:Adult; D015992:Body Mass Index; D001835:Body Weight; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008923:Missouri / Q000453:epidemiology; D011247:Pregnancy; D014427:Twins