div class=”ChapterContextInformation”>
37. The Retained Placenta
37.1 Background
The United Nations in 2000 have set Millennium Development Goals, one of which is to bring maternal mortality down by three quarters. To achieve the goal, postpartum haemorrhage (PPH)-related maternal deaths have to go down. Health workers of the low-resource countries need to have adequate relevant medication and to have training in first aid procedures. Most important, there is a need of evidence-based guidelines on the various interventions across the world. This will help to lay the foundation for the strategies, policies and programme development.
37.2 Introduction
Postpartum haemorrhage is an extremely important causative factor of maternal mortality in the developing world. Postpartum haemorrhage associated with retained placenta amounts to almost 0.6–3.3% of normal deliveries [1–3]. Mortality is very low if timely hospital care and blood banks are available. In PPH, the overall case fatality rate is high. The commonest cause of death is haemorrhage, especially when timely manual removal is not available or when approach to hospital is difficult. Hence an immediate and effective medical method of management has a major role in reducing the maternal mortality.
37.3 What Is PPH?
Postpartum haemorrhage is defined as blood loss more than or equal to 500 mL within 24 h of birth; severe PPH is blood loss greater than or equal to 1000 mL within 24 h. Postpartum haemorrhage is the commonest cause of maternal mortality. Majority of complications due to PPH occur in the first 24 h postdelivery (primary PPH), whereas any abnormal or excessive bleeding from the birth canal occurring between 24 h and 12 weeks postpartum is regarded as secondary postpartum haemorrhage.
37.4 What Is Retained Placenta?
The placenta retained in utero, with its commonest complication, PPH, is one of the nightmares of delivery events, which no ante-natal care can predict or even prevent [4, 5]. There are conditions, first, in which the placenta remains in the uterus, retained placenta, or second, an adherent placenta.
In retained placenta, the placenta may separate partially or completely, but due to an associated secondary complication (usually mechanical), it fails to expel from the uterus, the most common cause being uterine inertia.
37.4.1 Pathophysiology
The key factor is the retro-placental myometrium.
Brandt in 1993 explained the role of a uterine contraction in the process of detachment of the placenta from the decidual bed [6]. Herman first used ultrasonography to show that a retro-placental myometrial contraction is necessary to generate shearing forces between the placenta and myometrium which finally leads to its separation. He divided the third stage into four phases according to the ultrasound appearances [7].
In the latent phase, immediately after expulsion of the baby, the whole of the myometrium contracts apart from the retro-placental part. In the contraction phase, the retro-placental myometrium contracts leading to the separation of the placenta from the decidua. In the next phase, uterine contraction leads to placental expulsion. Contractions occurring prior to delivery are insufficient to cause placental separation as the foetus prevents the myometrium from achieving the necessary strain for detachment [8]; some of the authors hence omit the contraction stage from the classification [9]. These authors have elaborated the events using Doppler. They say that the blood flow through the arcuate and radial arteries is decreased during the latent phase and completely cuts off at the onset of the contraction phase [9]. This reduced blood flow is due to the myometrial ‘physiological ligature’. Hence maternal blood flow to the placenta stops prior to ‘placental detachment and only blood from the intervillous spaces is lost. USG studies also help to understand the causes of the retained placenta. The duration of the 3rd stage of labour depends on the duration of the latent phase and a prolonged 3rd stage is due to failure of contraction in the retro-placental area’. In the retained placenta, there is an overall failure of retro-placental contraction. Doppler studies confirm that the blood flow through the myometrium to the placenta continues irrespective of placenta accreta or prolonged latent phase [9], hence more chances of haemorrhage during manual removal of placenta. This also explains why partial or forced separation of the placenta prior to onset of the contraction phase is associated with high rates of haemorrhage. If the pro-contractile stimuli are strong enough, then labour can be successful despite of persisting, localised placental inhibition. But there will be more chance of retained placenta because of the strong persistent placental inhibition of retro-placental myometrial contractility [10–13].
Many local inhibitors have been identified. Progesterone is an important inhibitor of myometrial contractility in animals; its role in women is under evaluation. The anti-progesterone mifepristone sensitises myometrium to given prostaglandins and hence is used for induction of labour in all trimesters of pregnancy in humans [14–16]. Recent evidence, however, suggests reduction in progesterone metabolites as its mechanism of action [17, 18]. Nitric oxide, a powerful smooth muscle relaxant, is produced in large amount by nitric oxide synthase (NOS) in the placenta [19]. It is rapidly oxidised following its production. Exogenous NO seems to relax myometrium. A prolonged latent phase is an important cause of retained placenta. This could be either maintained by eliminating the inhibitor (e.g. by treatment with an anti-progesterone) or by stimulation with oxytocics. Umbilical vein oxytocin is a localised stimulus to the retro-placental myometrium [20–22].
37.5 Management of Retained Placenta
37.5.1 Manual Removal
Presently commonest mode of treatment for a retained placenta is its manual removal under anaesthesia though the female is exposed to risks of anaesthesia as well as infections. Both risk factors are higher in the developing world. The time that is allowed before manual removal may vary; recommended is a delay of ½–1 h in the absence of haemorrhage. There is no increase in haemorrhage till 30 min postpartum [1]; also between 30 and 60 min almost 40% more of placentae will be spontaneously expelled with the loss of an average of just about 0.3 L of blood [23].
There are multiple management options in cases of placenta accreta. Partial manual removal followed by curettage is used to remove maximum possible placenta. The remaining bits of trophoblast is usually reabsorbed spontaneously, but the B-HCG take longer to return to normal [24]. In the placenta percreta, blood continues to flow via the area of invasion even after the maximum part of the placenta is removed due to the lack of the myometrial physiological ligature which would normally cease the flow [9]. In a LSCS, the haemostasis may be achieved through myometrial bed ligatures or through uterine or internal iliac artery ligation [25]. At times, a hysterectomy may be required. If placenta percreta is diagnosed antenatally using ultrasound [9], then it is advisable to opt for conservative treatment. This involves leaving the placenta in situ after delivery. The levels of B-HCG are followed serially and manual removal and curettage performed if indicated [26]. Methotrexate may be beneficial [27].
37.5.1.1 WHO Recommendation
Stat dose of antibiotics (ampicillin or first-generation cephalosporin) post manual removal of the placenta (quality of evidence, very low; strength of recommendation, strong).
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
