34
Obstetric haemorrhage
Introduction
Obstetric haemorrhage is one of the leading causes of maternal mortality worldwide, and even in the more affluent societies, with ready access to resuscitation, uterotonics, blood transfusion and surgery, deaths still occur. Haemorrhage may be of rapid onset. It is important to recognize its severity promptly, institute effective therapy and keep ahead of the loss.
A vaginal examination should not be performed in the presence of antepartum vaginal bleeding without first excluding placenta praevia – ‘No PV until no PP’.
Definitions
Vaginal bleeding associated with intrauterine pregnancy is divided into the following categories:
threatened miscarriage – up to 24 weeks’ gestation
antepartum haemorrhage – from 24 weeks’ gestation until the onset of labour
intrapartum haemorrhage – from the onset of labour until the end of the second stage
postpartum haemorrhage – from the third stage of labour until the end of the puerperium (6 weeks after delivery).
Antepartum haemorrhage (APH)
APH affects 3–5% of pregnancies. Placental abruption and placenta praevia are the most important causes of APH but are not the commonest. The majority of APH remains unexplained after clinical and ultrasound examination.
Causes
Antepartum haemorrhage is classified according to the source of the bleeding.
Local
There may be bleeding from the vulva, vagina or cervix. Bleeding from the cervix is not uncommon in pregnancy and may follow sexual intercourse. A cervical ectropion or benign polyp is often found, and only very rarely is there cervical carcinoma. Later in pregnancy, the passing of a blood-stained ‘show’, mucus along with a small amount of blood, may simply herald the onset of labour as the cervix becomes effaced.
Placental
Placenta praevia
This is when the placenta encroaches upon the lower segment, with the lower segment arbitrarily defined on ultrasound scanning as extending 5 cm from the internal os. Placenta praevia is more common among women with a previous caesarean section but the majority of women with placenta praevia have no discernible risk factors. Transvaginal ultrasound is a reliable and safe method of determining the distance between the edge of the placenta and the internal os of the cervix. Placenta praevia is classified either as major or minor, or graded I–IV (Table 34.1, Fig. 34.1).
It is also important to note whether the placenta is anterior or posterior, as caesarean section is technically more difficult with an anterior placenta.
It is not possible to avoid haemorrhage in labour with a major placenta praevia, but it may be possible to deliver successfully with a minor degree of praevia. In the assessment of suitability for such a delivery, engagement of the presenting part is important together with the actual distance of the placenta from the internal os determined by ultrasound (Fig. 34.2). Those who do not have an at least partially engaged head should be delivered by caesarean section and a distance of at least 2 cm from placental edge to internal os is recommended before recommending vaginal birth. A low-lying placenta may be identified in an asymptomatic woman at the time of an ultrasound scan early in pregnancy and placental location is routinely determined at the time of the fetal anomaly scan at 20 weeks. As the uterus grows from the lower segment upwards, the placenta appears to move upwards with advancing gestation. In total, 2% of those with a low-lying placenta before 24 weeks; 5% of those at 24–29 weeks and 23% of those at 30 + weeks, will still have a placenta praevia at term. This is not a reflection of placental migration, but simply a feature of uterine growth. When a low-lying placenta is detected on ultrasound scanning early in pregnancy, it is necessary to repeat the scan early in the third trimester and then review the management if the placenta is still low.
The risk of placenta praevia is of a sudden, unpredictable, major haemorrhage and some clinicians advocate hospital admission from 30–32 weeks onwards, so that facilities for resuscitation and delivery are immediately available. This can be socially difficult for the woman, particularly if she has children at home, and immobility in hospital may predispose to thromboembolic disease. Outpatient management is frequently undertaken, particularly for those who have had no bleeding (placenta praevia an incidental ultrasound finding) or just light bleeding, and who live close to the hospital with good social support and available transport. Elective delivery is usually planned for 38–39 weeks, but will be earlier if there is a major haemorrhage.
Caesarean section in the presence of placenta praevia should be directly supervised or performed by a senior obstetrician, since a large blood loss is frequently encountered due to the relatively poor capacity of the lower segment of the uterus to contract.
Anterior placenta praevia in the presence of a history of one or more caesarean sections predisposes the woman to placenta accreta, where the placenta invades the myometrium and cannot be readily separated from the uterus following delivery. Placenta accreta can be diagnosed with ultrasound antenatally and MRI is increasingly being used to improve accuracy of diagnosis. The presence of placenta accreta markedly increases the chance of severe haemorrhage and a multidisciplinary approach to delivery is recommended. Severe haemorrhage can require hysterectomy and women should be warned of this possibility prior to surgery.
Placental abruption
Placental abruption is defined as retroplacental haemorrhage (bleeding between the placenta and the uterus) and usually involves some degree of placental separation. Its management depends on the amount of bleeding, presence or absence of maternal haemodynamic compromise, the maturity of the fetus and its condition. Separation of the placenta results in a reduced area for gas exchange between the fetal and maternal circulations predisposing to fetal hypoxia and acidosis. It is crucial to remember that with placental abruption the amount of ‘revealed’ blood (bleeding from the vagina) may not reflect the total blood loss and, indeed, a woman may have considerable retroplacental bleeding without any external loss at all – a ‘concealed abruption’, the most hazardous type of abruption (Fig. 34.3).
History of a previous pregnancy affected by placental abruption and maternal cigarette smoking are among the risk factors for placental abruption, but the majority of placental abruptions occur by chance in women without identifiable risk factors.
Light bleeding from the edge of a normally situated placenta does not normally compromise the fetus and a brief episode of inpatient observation with subsequent surveillance of fetal growth with serial ultrasound fetal biometry is appropriate until delivery at term.
Major revealed haemorrhage is obvious, and urgent delivery is usually required. A major concealed abruption is inferred from the degree of pain, uterine tenderness and evidence of hypovolaemic shock; again, urgent delivery may be required. The decision between vaginal delivery and caesarean section is influenced by the degree of bleeding, maternal and fetal conditions.
