Epidemiology of retained placenta: oxytocin as an independent risk factor.

OBJECTIVE

To identify factors related to retained placenta in the context of contemporary obstetric practice.

METHODS

This was a case-control study comparing 408 cases of retained placenta and an equivalent number of control individuals. Epidemiological and delivery-related variables were registered in computerized prenatal and in-hospital medical records. Univariable and multivariable logistic regressions were used for estimation of risk ratios and statistical significance.

RESULTS

Independent risk factors for retained placenta were: previous retained placenta (odds ratio [OR] 12.61, 95% confidence interval [CI] 3.61-44.08); preterm delivery (OR 3.28, 95% CI 1.60-6.70); oxytocin use for 195-415 minutes (OR 2.00, 95% CI 1.20-3.34); oxytocin use more than 415 minutes (OR 6.55, 95% CI 3.42-12.54, number needed to harm 2.3); preeclampsia (OR 2.85, 95% CI 1.20-6.78); two or more previous miscarriages (OR 2.62, 95% CI 1.31-5.20); and one or more previous abortion (OR 1.58, 95% CI 1.09-2.28). Parity of two or more had a seemingly protective effect (OR 0.40, 95% CI 0.24-0.70), as did smoking at the start of pregnancy (OR 0.28, 95% CI 0.09-0.88). Retained placenta was significantly associated with an increased risk of postpartum hemorrhage. The OR related to blood loss exceeding 500 mL, 1,000 mL, and 2,000 mL and the need for blood transfusion was 33.07 (95% CI 20.57-53.16), 43.44 (95% CI 26.57-71.02), 111.24 (95% CI 27.26-454.00), and 37.48 (95% CI 13.63-103.03), respectively. Diabetes was numerically overrepresented in the case group, but the power of the study to detect a significant difference in risk outcome was insufficient.

CONCLUSION

Identifying risk factors for retained placenta is important in the assessment of women after delivery. The increased risk associated with duration of oxytocin use is of interest, considering its widespread use.

LEVEL OF EVIDENCE: II.