Retained placenta

The third stage of labour commences with the completed delivery of the fetus and ends with the completed delivery of the placenta and its attached membranes. The length of the third stage itself is usually 5-15 minutes. The National Institute for Health and Care Excellence (NICE) recommends that the third stage is diagnosed as delayed if it takes longer than 30 minutes to deliver the placenta with active management or 60 minutes if allowed to deliver the placenta physiologically with maternal effort¹ .

Retained placenta is important as it is one of the causes of hemorragia pós-parto, which is the third leading cause of maternal mortality in the UK² . Retained placenta increases the risks of a postpartum haemorrhage by five-fold (3.36-7.87; 99% confidence interval (CI))³ .

Etiologia

There are three main types of retained placenta following vaginal delivery, which can all be treated by manual removal of the placenta⁴ :

• Placenta adherens, when the myometrium fails to contract behind the placenta.

• Trapped placenta, when a detached placenta is trapped behind a closed cervix.

• Partial accreta, when there is a small area of adherent placenta preventing detachment.

Rarely there is an abnormality of the placenta (placenta accreta) which leads it to penetrate the myometrium to a varying degree preventing manual removal without risking significant postpartum haemorrhage.

The incidence and importance of retained placenta vary greatly around the world⁴ .

• In less developed countries, it affects about 0.1% of deliveries but has up to 10% case fatality rate.

• In more developed countries, it is more common (about 3% of vaginal deliveries) but very rarely associated with mortality. Retained placenta was identified as the cause of 18% of severe obstetric haemorrhages in one American series⁵ .

Active management of the third stage is encouraged as it is associated with a lower risk of hemorragia pós-parto and blood transfusion. If the labour has progressed normally and the mother requests physiological management of the third stage, she should be supported in this request^{1 6} . However, if there has been significant haemorrhage, try to discover if the placenta has separated - as indicated by:

• A sudden rush of blood.

• Fundus moves higher and becomes rounded.

• Increase in length of part of the umbilical cord visible at the vulva.

• Raising of fundus does not cause the cord to decrease in length.

If the placenta has separated:

• Try to deliver the placenta by 'rubbing up' the uterus.

• Then push it towards the vagina to help with expulsion of the placenta and membranes.

• These are held and twisted whilst pulling constantly so that membranes are kept intact.

If the placenta does not deliver, offer a vaginal examination and if this finds no evidence that the placenta has detached, IV access should be obtained. If there is excessive bleeding,give IV oxytocic agent to produce a contraction but it should not be used routinely. If the woman is not already in an obstetric unit, she should be transferred urgently. She should be observed frequently to assess the need for resuscitation¹ .

If the placenta needs to be removed manually, this must be done under anaesthetic:

• Place a gloved hand into the uterus, with the other hand on the fundus to control it.

• Follow the umbilical cord until you find the lower edge of the placenta.

• Push the hand between the placenta and the body of the uterus and ease the placenta away with a sawing action (NB: in cases of placenta accreta, the placenta will not detach easily and use of excessive force can result in life-threatening haemorrhage which may require hysterectomy).

• When fully detached, explore the uterine cavity for damage and for other pieces of placenta.

• Massage the fundus with one hand whilst extracting the placenta and membranes with the hand in the uterine cavity.

• Look carefully at the placenta to be sure that it is complete.

• Intravenous oxytocic agents should not be used routinely to deliver a retained placenta. However intravenous oxytocic agents should be used if the placenta is retained and the woman is bleeding excessively. Oxytocin is preferred to ergometrine.

• Retained placenta is, in itself, life-threatening because of its association with infection and hemorragia pós-parto.

• Manual removal of a retained placenta is not without risk. Although it increases the likelihood of bacterial contamination in the uterine cavity, there are no randomised controlled trials to evaluate the effectiveness of antibiotic prophylaxis to prevent endometrite after manual removal of placenta⁷ .

Since manual removal of a retained placenta is invasive and carries risks of damage to the genital tract, infection and haemorrhage, many attempts have been made to increase the ability of the uterus to expel a retained placenta without recourse to surgery.

• Umbilical vein injections of saline, plasma expander or prostaglandins with or without oxytocin have all been studied. Unfortunately, a Cochrane review found no evidence of any beneficial effect of any of these⁸ . Also, NICE no longer recommends umbilical vein injection of oxytocin¹ .

• There is conflicting evidence from small studies that nitroglycerine, sublingual or IV, may reduce the need for a manual removal of retained placenta; the true effect is uncertain.

• Sulprostone is a potent stimulator of uterine smooth muscle contractions with high abortifacient activity. It is not licensed in the UK but has been shown in one small study (n=50) to reduce the need for the manual removal of the placenta by 49%⁹ and in a study of 126 women, all of whom received sulprostone, by 39.7%.

• Misoprostol does not reduce the need for manual removal for retained placenta¹⁰ .