Reoccurrence of retained placenta at vaginal delivery: an observational study.

Objective: To estimate the prevalence and validate the diagnosis of retained placenta in nulliparous women and the risk of reoccurrence at subsequent vaginal delivery.
Design: Nested cohort study.
Setting: Department of Gynecology and Obstetrics, university-affiliated teaching hospital.
Population: 10 334 nulliparous singleton pregnancies who delivered vaginally at the hospital during 2000-2009.
Methods: Data from a computerized database information system were used to identify 287 women who had an ICD-10 diagnosis of retained placenta and 572 randomly selected controls matched by the date of first delivery. At chart review the diagnosis was confirmed by: (1) excessive bleeding <30 minutes after delivery without placental separation, (2) placenta not separated 30 minutes after delivery or (3) confirmation of retained placental tissue >2 hours postpartum.
Main Outcome Measures: Confirmation of the diagnosis and prevalence of retained placenta. Risk of reoccurrence in a subsequent vaginal delivery.
Results: The prevalence of retained placenta increased from 2.8 to 7.0% after confirmation according to the set criteria. Of the selected women, 48.4% had a subsequent vaginal delivery. Of these women, 25.3% (23/91) with a previous retained placenta and 5.3% (11/206) without previously retained placenta, experienced retained placenta in subsequent delivery. This corresponds to an adjusted odds ratio of 5.5 (95% confidence interval 2.6-12.7) in the multivariate analysis for recurrence of retained placenta in a subsequent vaginal delivery.
Conclusions: The use of the ICD-10 diagnosis of retained placenta underestimated the prevalence. The risk of reoccurrence of retained placenta is significantly increased in a subsequent vaginal delivery.
(© 2012 The Authors Acta Obstetricia et Gynecologica Scandinavica © 2012 Nordic Federation of Societies of Obstetrics and Gynecology.)