Sonographic examination of uteroplacental separation during the third stage of labor

To characterize patterns of uteroplacental separation during the third stage of labor, and to investigate their association with previous history of Cesarean section (CS), delays in placental separation and blood loss.

In this cohort observational study, continuous ultrasound imaging of uteroplacental separation was performed during the third stage of labor in 78 vaginal deliveries. All women were primiparous and were divided into two groups: those with a previous vaginal delivery (n = 62) and those who had undergone CS (n = 16).

Three patterns of separation were observed: 'down-up' (n = 64), 'up-down' (n = 12) and 'bipolar' (n = 2). Bipolar separation was observed only with fundal placentae. Up-down separation was significantly associated with a history of CS (P < 0.001; odds ratio 14.0; 95% CI, 3.4-57.4) and a longer second stage of labor (P = 0.02).

In most cases, uteroplacental separation begins at the lower placental pole and proceeds upwards. Women with a history of CS have a higher rate of up-down separation, possibly owing to impaired lower uterine segment contractility.