Placenta praevia--a review with emphasis on the role of ultrasound

Ultrasound Techniques and Follow-Up Exaninations in Placenta Previa

In placenta previa, the placenta occupies a position near the internal os at or after 28 weeks of gestation. Ultrasound examination has been used to diagnose placenta previa in 6% of the general population during the first trimester of pregnancy. More than 90% of these cases undergo placental conversion by the third trimester. This conversion (commonly called migration) is caused by the differing growth patterns of the uterine corpus and the lower uterine segment. To correctly diagnose placenta previa, it is crucial to utilize all available ultrasound techniques, including endovaginal and translabial scanning. This retrospective study examines the timing and the techniques of follow-up ultrasound examination in placenta previa.

The role of transvaginal sonography in the diagnosis of placenta praevia

Transvaginal sonography was performed in 70 patients diagnosed to have placenta praevia by transabdominal sonography. The diagnosis was confirmed either by digital examination in theatre at term or operative finding at delivery. Forty-nine cases (70%) were correctly diagnosed to have placenta praevia by both modes of sonography. Transvaginal sonography ruled out placenta praevia in 12 cases (17%) thought to be placenta praevia by transabdominal ultrasound. Both transabdominal and transvaginal sonography demonstrated 'placental migration' in 4 cases (6%) which were no longer praevia at delivery. Five patients (7%) were erroneously believed to have placenta praevia by both sonographic techniques. Overall, the diagnostic accuracy of transvaginal sonography was 92.8% compared with 75.7% for transabdominal sonography. None of the subjects experienced any exacerbation of bleeding or other complications. The results suggest that transvaginal sonographic localization of the placenta is safe and superior to the transabdominal route.

Do women with placenta praevia without antepartum haemorrhage require hospitalization?

Patients with placenta praevia in the third trimester are routinely confined to hospital for fear of major haemorrhage. Whilst this is arguably necessary for those who have had an episode of antepartum haemorrhage (APH), it is uncertain whether these same management principles are valid for those with placenta praevia without antepartum haemorrhage. A retrospective study was undertaken reviewing the case records of 69 consecutive patients diagnosed with placenta praevia in the third trimester of pregnancy. The outcome of 15 who had had no episodes of bleeding were compared with those who had at least 1 antepartum bleeding episode. Patients with placenta praevia without evidence of APH spent a significantly shorter amount of time in hospital and had a significantly lower rate of emergency delivery, with a neonatal outcome as good if not better than the APH group. We conclude that outpatient management in this cohort of patients may be a safe and cost-effective means of care, and warrants randomized prospective study.