Underlying mechanisms of retained placenta: Evidence from a population based cohort study.

ABSTRACT

OBJECTIVE: To determine risk factors for retained placenta, and to identify supporting epidemiologic evidence for the three previously-proposed mechanisms (i) invasive placentation, (ii) placental hypo-perfusion, and (iii) inadequate uterine contractility. DESIGN: A retrospective population-based cohort study. SETTING AND POPULATION Israeli population in the southern district. METHODS: Data were analyzed from a tertiary hospital database, between 1989 and 2014, using univariate tests and generalized estimating equation (GEE) multivariable models. MAIN OUTCOME MEASURES: Prevalence of retained placenta. RESULTS: The study population included 205,522 vaginal deliveries of which 4.8% (n=9870) were complicated with retained placenta. Previous intra-uterine procedures and placenta-related pregnancy complications were found to be significant risk factors for retained placenta (history of cesarean section aOR=8.82, 95%CI 8.35-9.31; history of curettage aOR=12.80, 95%CI 10.57-15.50; pre-eclampsia aOR=1.25, 95%CI 1.14-1.38; delivery of a small for gestational age neonate aOR=1.08, 95%CI 1.01-1.16; stillbirth aOR=2.34, 95%CI 1.98-2.77). During labour, the risk for retained placenta was increased in presence of arrest of dilatation (aOR=2.03, 95%CI 1.08-3.82) or arrest of descent (aOR=1.55, 95%CI 1.22-1.96). Infections of the uterine cavity during labour were also found to be strongly associated with increased risk of retained placenta (endometritis aOR=2.21, 95%CI 1.64-2.97; chorioamnionitis aOR=3.35, 95% CI 2.78-4.04). CONCLUSIONS: Supporting epidemiologic evidence were found for all three underlying mechanisms. In addition, there is evidence to suggest that intrauterine infection and inflammation may also be a possible pathology associated with retained placenta. TWEETABLE ABSTRACT Risk factors for retained placenta support previously proposed mechanisms in a large cohort study.