Absence of retained placenta in a previous delivery does not predict its absence in a subsequent delivery: a retrospective cohort study

A history of retained placenta (RP) increases the recurrence rate of RP in subsequent pregnancies. However, no studies have examined whether the risk of RP is reduced in subsequent pregnancies among women without RP in their previous delivery. To address this knowledge gap, we examined whether the absence of RP at first delivery was associated with a lower risk of RP at subsequent delivery. This retrospective cohort study was conducted at a birth clinic for low-risk women. Three hundred women with low-risk pregnancies who delivered their first and second full-term singleton babies vaginally were included (second delivery between May 2021 and March 2022). Data from the first and second deliveries of the same women were linked and analyzed. RP was defined solely on the basis of a prolonged third stage of labor (≥ 30 min). The primary outcome was the predictive value of RP status at the first delivery for RP occurrence at the second delivery. Among the 293 women without RP in the first delivery, 286 (97.6%) remained free of RP in the second delivery, whereas 7 (2.4%) developed a new RP. Among the 7 women with RP in the first delivery, RP recurred in 1 woman (14.3%). The absence of RP in the first delivery was not predictive of the absence of RP in the second delivery (negative likelihood ratio, 0.89; 95% CI, 0.69–1.16). No significant difference in third-stage duration was observed between the first and second deliveries. We found no evidence that the absence of RP at the first delivery predicted a lower risk of RP at the subsequent delivery. Therefore, the absence of RP in a previous delivery should not be assumed to indicate a lower risk in a subsequent delivery.