Ultrasound
- Transabdominal US is the standard method of evaluating patients with antepartum haemorrhage, but resuscitation takes priority over any form of imaging. 4
- The results of transabdominal US are improved when the patient has a full bladder. However this itself can distort the anatomy of the lower uterine segment, making visualisation of the placenta and the internal os difficult. The shadow cast by the pubic symphysis may also obscure the imaged area. 4,5
- In such cases, transvaginal or transperineal US are indicated as they are more sensitive, specific and accurate than transabdominal US. However, there are no randomised trials that directly compare the different approaches. 6
- With skilled operators, transvaginal US is not associated with an increase in the rate of haemorrhage or adverse outcomes as the focal length of the ultrasound beam is usually between 2 to 7 centimetres. 4
- For placenta previa, the sensitivity and specificity for transabdominal US is 79%-82%, and 38%-97% respectively. If the placenta is noted to be previa early in pregnancy, a repeat ultrasound is recommended between 32 to 34 weeks gestation. 4
- The sensitivity for placental abruption is low and this remains a clinical diagnosis. 1,7
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