The retained placenta is a significant cause of maternal mortality and morbidity throughout the developing world. It complicates 2% of all deliveries and has a case mortality rate of nearly 10% in rural areas.
Ultrasound studies have provided fresh insights into the mechanism of the third stage of labour and the aetiology of the retained placenta. Following delivery of the baby, the retro-placental myometrium is initially relaxed. It is only when it contracts that the placenta shears away from the placental bed and is detached. This leads to its spontaneous expulsion. Retained placenta occurs when the retro-placental myometrium fails to contract. There is evidence that this may also occur during labour leading to dysfunctional labour. It is likely that this is caused by the persistence of one of the placental inhibitory factors that are normally reduced prior to the onset of labour, possibly progesterone or nitric oxide.
Presently, the only effective treatment is manual removal of placenta (MROP) under anaesthetic. This needs to be carried out within a few hours of delivery to avoid haemorrhage. For women in rural Africa, facilities for MROP are scarce, leading to high mortality rates. Injection of oxytocin into the umbilical vein has been suggested as an alternative. This method relies on the injected oxytocin passing through the placenta to contract the retro-placental myometrium and cause its detachment. Despite several placebo controlled trials of this technique, no firm conclusion have been reached regarding its efficacy. This may be due to inadequate delivery of the oxytocin to the placenta. Further trials are in progress to assess the optimal dose of oxytocin as well as the efficacy of a new technique designed to improve delivery of the oxytocin to the placental bed.