Risk factors for retained placenta

Abstract

Objective: Retained placenta complicates 2-3% of vaginal deliveries and is a known cause of postpartum hemorrhage. Treatment includes manual or operative placental extraction, potentially increasing risks of hemorrhage, infections, and prolonged hospital stays. We sought to evaluate risk factors for retained placenta, defined as more than 30 minutes between the delivery of the fetus and placenta, in a large US obstetrical cohort.

Study design: We included singleton, vaginal deliveries ≥24 weeks (n = 91,291) from the Consortium of Safe Labor from 12 US institutions (2002-2008). Multivariable logistic regression analyses estimated the adjusted odds ratios (OR) and 95% confidence intervals (CI) for potential risk factors for retained placenta stratified by parity, adjusting for relevant confounding factors. Characteristics such as stillbirth, maternal age, race, and admission body mass index were examined.

Results: Retained placenta complicated 1047 vaginal deliveries (1.12%). Regardless of parity, significant predictors of retained placenta included stillbirth (nulliparous adjusted OR, 5.67; 95% CI, 3.10-10.37; multiparous adjusted OR, 4.56; 95% CI, 2.08-9.94), maternal age ≥30 years, delivery at 24 0/7 to 27 6/7 compared with 34 weeks or later and delivery in a teaching hospital. In nulliparous women, additional risk factors were identified: longer first- or second-stage labor duration, whereas non-Hispanic black compared with non-Hispanic white race was found to be protective. Body mass index was not associated with an increased risk.

Conclusion: Multiple risk factors for retained placenta were identified, particularly the strong association with stillbirth. It is plausible that there could be something intrinsic about stillbirth that causes a retained placenta, or perhaps there are shared pathways of certain etiologies of stillbirth and a risk of retained placenta.

Keywords: postpartum hemorrhage; preterm birth; retained placenta; stillbirth.

FIGURE 1. Case selection diagram

GA, gestational age.

FIGURE 2. Retained placenta in nulliparous women by gestational age compared to 24 0/7 to 27 6/7

The adjusted odds ratios were adjusted for parity, maternal age, gestational age, admission BMI, race, history of abortion, history of cesarean delivery, large for gestational age (defined at >90% fetal weight), intrauterine growth restriction (defined as <5% fetal weight), duration of first and second stages of labor, duration of rupture of membranes to delivery, labor induction agent, group B streptococcal status, chorioamnionitis, use of epidural, episiotomy, stillbirth, hospital type, and duration of exposure to oxytocin. BMI, body mass index.

FIGURE 3. Retained placenta in multiparous women by gestational age compared to 24 0/7 to 27 6/7

The adjusted odds ratios were adjusted for parity, maternal age, gestational age, admission BMI, race, history of abortion, history of cesarean delivery, large for gestational age (defined at >90% fetal weight), intrauterine growth restriction (defined as <5% fetal weight), duration of first and second stages of labor, duration of rupture of membranes to delivery, labor induction agent, group B streptococcal status, chorioamnionitis, use of epidural, episiotomy, stillbirth, hospital type, and duration of exposure to oxytocin. BMI, body mass index.