1、Retained placenta can be defined as lack of expulsion of the placenta within 30 minutes of delivery of the infant . This is a reasonable definition in the third trimester when the third stage of labor is actively managed (ie, administration of a uterotonic agent before delivery of the placenta, controlled cord traction) because 98 percent of placentas are expelled by 30 minutes in this setting
2、Physiological management of the third stage (ie, delivery of the placenta without the use of uterotonic agents or cord traction) increases the frequency of retained placenta: only 80 percent of placentas are expelled by 30 minutes and it takes about 60 minutes before 98 percent of placentas are expelled. In the second trimester, the frequency of retained placenta at 30 minutes is also high; most are expelled by 90 to 120 minutes
3、The three types of retained placenta, in order of increasing morbidity, are:
●Trapped or incarcerated placenta – The incarcerated or trapped placenta is simply a separated placenta that has detached completely from the uterus, but has not delivered spontaneously or with light cord traction because the cervix has begun to close.
●Placenta adherens – The placenta is adherent to the uterine wall, but easily separated manually.
●Placenta accreta spectrum – The placenta is pathologically invading the myometrium due to a defect in the decidua. It cannot be cleanly separated, although the placenta may still be removed vaginally if the area of attachment is small.
4、The overall prevalence of retained placenta varies across settings and over time. In a systematic review of observational studies, the median prevalence of retained placenta at 30 minutes in high-resource settings was 2.7 percent of vaginal deliveries compared with 1.5 percent in low-resource settings. The prevalence has also been increasing
5、The two most common complications of retained placenta are postpartum hemorrhage and postpartum endometritis.
6、Severe bleeding is an obstetric emergency that requires prompt intervention. The retained placenta should be manually removed as soon as possible. Expulsion of the placenta promotes global uterine contraction and will likely reduce bleeding.
7、 When the placenta has been retained for 30 minutes in a stable patient delivered in the third trimester, we perform a physical examination (and sometimes ultrasound) to determine whether the placenta is merely trapped or still adherent and begin preparations for intervention. The optimum timing of intervention balances the risk of leaving the placenta in situ (postpartum hemorrhage) and the risks of intervention (postpartum hemorrhage and/or infection, uterine trauma) versus the likelihood that the placenta will spontaneously deliver with expectant management.
8、There is no consensus worldwide as to when intervention is indicated. We suggest discontinuing expectant management at 60 minutes. Available data suggest that delaying intervention until at least 30 minutes have elapsed will lead to spontaneous delivery of many placentas, and the risk of hemorrhage does not begin to increase until 20 to 30 minutes after birth. This time period could be extended beyond 60 minutes for deliveries in the second trimester where the risk of retained placenta is higher and the risk of hemorrhage is lower. but we suggest not delaying intervention by more than two hours from delivery of the infant due to the risk of infection and bleeding
9、 Gentle controlled cord traction alone may result in successful delivery of a trapped or incarcerated placenta or promote separation of placenta adherens. For the Brandt-Andrews maneuver, one hand is placed on the abdomen to secure the uterine fundus and prevent uterine inversion while the other hand exerts sustained downward traction parallel to the direction of the birth canal on the umbilical cord. Care should be taken to avoid avulsion of the cord.
10、If the lower uterus/cervix is contracted, thereby preventing expulsion of the placenta, administering nitroglycerin (glyceryl trinitrate) will relax smooth muscle in the myometrium and cervix and facilitate placental delivery
11、Manual extraction of the placenta is performed if controlled cord traction and drug therapy (when indicated as described above) do not lead to delivery of the retained placenta. Manual extraction of the placenta increases the risk of endometritis . For this reason, we agree with the World Health Organization (WHO) recommendation to administer prophylactic antibiotics
12、We believe there is no role for routine uterine curettage or aspiration after manual extraction. It has no documented benefit and carries the risk of uterine perforation and Asherman syndrome
13、Management of refractory or complicated cases： If digital extraction is not possible, large-headed forceps (eg, Bierer forceps, ring forceps) can be used to grip and extract the placenta in pieces or as intact specimen; ultrasound guidance can be helpful.
14、Incomplete extraction — During manual placental extraction, the clinician may note a small area where the placenta is very adherent to the uterus. This can usually be managed by slow persistent finger dissection to create a plane of separation at the maternal-placental interface. The plane of dissection is often partially through the placenta in these cases, which leaves some placenta adherent to the decidua and myometrium. This will not lead to postpartum hemorrhage as long as the uterus contracts well and there is no area of subinvolution at the site of the retained placental fragments. Curettage should be avoided, if possible, as the myometrium may be very thin at the point of adherence, thus increasing the risk of perforation. Curettage of the postpartum uterus also increases the risk of formation of intrauterine adhesions (Asherman syndrome).However, if placental tissue is retained and the patient is bleeding excessively, then curettage using a large blunt placental curette or aspiration is reasonable to remove the remaining placental tissue.
15、Unexpected placenta accreta spectrum — Rarely, the placenta accreta spectrum is first recognized at the time of manual removal of the placenta. In these cases, there is no plane of dissection between the uterus and placenta and, almost invariably, attempts at manual removal lead to life-threatening hemorrhage. We suggest administration of uterotonic drugs and preparation for hysterectomy, which is the definitive therapy.
16、Unproven and ineffective approaches — There is no high-quality evidence that any pharmacologic therapy is effective for expulsion of placenta adherens in patients who have been managed with parenteral oxytocin and cord traction as part of active management of the third stage of labor .
It has been hypothesized that administration of an additional uterotonic drug may be effective in this setting, in part because placenta adherens appears to result from contractile failure in the retroplacental area. Although ergot derivatives cause the uterus to contract, limited evidence suggests these drugs are no more effective than oxytocin alone . Furthermore, a powerful, continuous uterine contraction makes subsequent manual extraction more difficult.