Placenta abruption
Placenta abruption is the premature separation of the placenta prior to the third stage of labour and it is associated with severe maternal and fetal morbidity and increased perinatal mortality of up to 12% (59).
Variable incidence rates of placenta abruption have been reported in different populations, with 0.2-1% of pregnancies affected (60).Risk factors
The major risk factors for the occurrence of placenta abruption include a previous history of abruption, hypertensive disorders, or abdominal trauma, while modifiable risk factors include smoking and cocaine use (Box 22.7). Previous abruption is associated with a recurrence risk of 4.4%. This increases to 19-25% after two or more abruptions (16).
Some of the risk factors associated with abruption have synergistic effects (hypertension and cigarette smoking), hence the importance of antenatal education and intervention to encourage behaviour modifications with regard to substance misuse during pregnancy (61).
Classification
Attempts have been made to classify and grade placental abruption based on the severity in a similar fashion to placenta praevia (Box 22.8); however, this is not consistently used in day-to-day clinical practice where a more practical triaging into mild, moderate, or severe abruption is used based on the overall assessment of maternal and fetal well-being.
Pathophysiology
In a significant number of cases of placenta abruption, an underlying chronic placental disease exists. Abnormalities in the development of the spiral arteries in combination with decidua necrosis and vascular disruption lead to bleeding with or without an obvious trigger (62, 63). The initial bleeding occurs from disruption of maternal vessels in the decidua basalis and the accumulated blood or clot progressively separates the interface between the placenta and the decidua leading to partial or complete separation of the placenta.
This process may be self-limiting and contained or continuous especially in the high-pressure arterial bleeding in the central area of the placenta leading to rapid detachment and haemorrhage, with evident maternal and fetal compromise (64). In high-pressure bleeding from maternal vessels in the decidua basalis, some blood will track in between the myometrium towards the uterine serosa leading to the classic appearance of a couvelaire uterus. Abruption resulting from mechanical-related events (abdominal trauma, sudden uterine decompression from ruptured membranes) is thought to be caused by rapid shearing forces applied to the relatively inelastic placenta from sudden stretching or contraction of the uterine wall (62, 63). Placenta abruption resulting from maternal cocaine use may be related to the intense vasoconstriction induced by cocaine with consequent ischaemia and disruption of vessels (65).The production and release of thrombin accounts for the clinical sequelae observed in placenta abruption. The initial bleeding from the decidua stimulates the production of thromboplastin which then releases thrombin (66). Thrombin is a uterotonic agent and its release in placenta abruption is associated with uterine hypertonia and when in excess in the maternal circulation, it sets the stage for severe bleeding from an overwhelmed haemostatic system and widespread intravascular fibrin deposition (disseminated intravascular coagulopathy) (67).
Box 22.8 Classification of placenta abruption
Box 22.7 Risk factors for placenta abruption
• Hypertensive disorder:
— Pre-eclampsia
— Chronic hypertension
• Abdominal trauma
• Placental insufficiency
• Polyhydramnios
• Spontaneous rupture of membranes
• Smoking
• Cocaine use
• Multiparty
0: asymptomatic
Retrospective diagnosis.
1: mild
No or mild bleeding, slightly tender uterus, no maternal or fetal compromise, no coagulopathy.
2: moderate
No or moderate vaginal bleeding, moderate to severe uterine tenderness, maternal haemodynamic compromise, fetal distress, hypofibrinogenaemia.
3: severe
No or heavy vaginal bleeding, tetanic uterus, maternal haemodynamic compromise, coagulopathy, fetal death.
Box 22.9 Complications of abruption
• Fetal death
• Fetal distress
• Massive obstetric haemorrhage
• Disseminated intravascular coagulopathy
• Acute kidney injury
• Multiorgan failure
• Caesarean hysterectomy for postpartum haemorrhage
Clinical features
Pregnant women with placental abruption typically present with vaginal bleeding associated with abdominal or lower back pain and uterine contractions. The pain could be constant in nature or intermittent. The presence of known risk factors or triggers should heighten the suspicion of placenta abruption. Clinical examination may reveal pallor, maternal tachycardia, and hypotension in severe blood loss. The abdomen is typically tender with a firm to hard feel. The distinctive feel on abdominal palpation in severe abruption is described as ‘woody hard' caused by uterine hypertonus. In severe abruption with more than 50% of the placenta separated, evidence of fetal heart rate abnormalities and coagulopathy may be present. Complications of abruption are listed in Box 22.9.
The observed bleeding in these patients does not necessarily reflect the extent of haemorrhage because a significant amount of blood can be trapped in the retroplacental space also termed ‘concealed abruption'; therefore, decisions regarding ongoing management should be based on the overall assessment of maternal and fetal status and laboratory investigations.
The diagnosis of placenta abruption is mainly clinical. The investigations performed are aimed at assisting in the triaging and further management.
Assessment and resuscitation
The initial assessment and resuscitation should follow the principles described in the initial assessment of patients with APH. Laboratory investigations in suspected cases include a full blood count, group and crossmatch where it is considered moderate or severe, coagulation profile (prothrombin time, activated partial thromboplastin time, fibrinogen), liver function tests, renal function tests, and Kleihauer-Betke test.
A toxicology screen should be performed in suspected cases of substance misuse. Where facilities are available, the use of real-time point-of-care tests of coagulation (e.g. ROTEM), could be particularly helpful in providing an early indication of clotting derangement which allows for timely correction with appropriate blood and blood products.The role of ultrasonography in the assessment of patients with suspected placenta abruption is limited but this can exclude placenta praevia. However, it has a limited role in those patients who are previously known to have fundal placenta location, as the sensitivity of ultrasound findings for the diagnosis of abruption is relatively low (25-50%) (68).
Transfusion of blood and blood products
The possibility of blood transfusion and transfusion of blood products must always be anticipated in patients with clinical suspicion of abruption. Appropriate preparations must therefore be made. In severe abruption with evidence of maternal haemodynamic compromise, coagulopathy, or fetal death, prompt replacement of blood and blood products must be expeditiously done. This can be achieved in a timely manner by activating the massive blood transfusion protocol. The typical protocol will deliver 6 units of packed red blood cells, 6 units of fresh frozen plasma, two pools of cryoprecipitate (10 units), and six pools of platelets. Fibrinogen at a dose of 2 g should be made available as well. Once the estimated blood loss exceeds 500 mL in placenta abruption, blood transfusion should be initiated while awaiting the results of laboratory investigations. Coagulation studies should be frequently monitored in these patients until there is a trend towards normality.
Delivery
The decision on whether to embark on expediting delivery or to pursue expectant management depends on the presence or absence of significant maternal or fetal compromise. In the presence of fetal compromise or fetal death, delivery should be expedited.
This should also be the case when there is evidence of significant coagulopathy and active bleeding.When vaginal delivery is not imminent and there is evidence of fetal distress, a caesarean delivery should be performed. However, if intrauterine fetal death has already occurred, vaginal delivery is the preferred mode of delivery with transfusion of blood and blood products as required to correct coagulopathy.
In those patients who have been stabilized after the initial resuscitation and are at more than 34 weeks' gestation with regular contractions, expedited vaginal delivery should be the goal unless there are obstetric contraindications to vaginal birth. These patients usually deliver relatively quickly following amniotomy.
Conservative management is only appropriate in stable preterm pregnancies (be administered given the increased risk of preterm delivery in these patients. The role of tocolysis is debatable and routine use is not recommended. Patients with preterm abruption on expectant management should be monitored very closely until delivery, which should be considered by 37-38 weeks' gestation in those patients who remain stable after initial presentation with preterm mild clinical abruption (69).
Postpartum care
Close monitoring of patients with complications of abruption (Box 22.8) should be carried out in a critical care setting after delivery. Monitoring and correction of coagulation status and regular maternal vital signs should be carried out. Patients who have suffered severe abruption particularly those with poor outcome should be properly debriefed about the peripartum events by a senior clinician prior to discharge from the hospital. Additionally, these patients will benefit from a follow-up when a plan of care for any subsequent pregnancies can be discussed. The likelihood of recurrence in a subsequent pregnancy is 3-15% (70) and the need for antenatal awareness should be emphasized.