The incidence of placental attachment disorders continues to increase with rising caesarean section rates. Antenatal diagnosis helps in the planning of location, timing and staffing of delivery. In at-risk women grey-scale ultrasound is quite sensitive, although colour ultrasound is the most predictive. Magnetic resonance imaging can add information in some limited instances. Patients who have had a previous caesarean section could benefit from early (before 10 weeks) visualisation of the implantation site.Current data refer only to placentas implanted in the lower anterior uterine segment, usually over a caesarean section scar.

The purpose of this study was to determine in what percentage of cases the assessment of placental localization using transabdominal sonography (TAS) was changed after transvaginal sonography (TVS) was applied. TVS was prospectively performed on all pregnant women of at least 15 weeks' gestation, when the placental edge using TAS appeared to be over or within 2 cm (low-lying) of the internal cervical os. The time required for the TVS scan and the distance of the placental edge from the internal cervical os were recorded. Of the 168 patients entered into the study, 131 were analyzed. Landmarks were poorly seen in 50% of the cases when using TAS. In 66 cases, the placenta appeared low or possibly over the internal cervical os using TAS, but a definitive diagnosis could not be made due to suboptimal visualization. In the remaining 65 cases, visualization of the internal os and placental edge was possible using both TAS and TVS. In this group, there was a change in the diagnosis in 26% of the cases after TVS was performed. Our results suggest that optimal visualization of the placental edge and internal cervical os is usually difficult with TAS when the placenta appears low-lying or over the internal cervical os. The assessment of placental localization was changed in over one-quarter of cases (26%) after transvaginal sonography was performed. The use of transvaginal ultrasound should be seriously considered when the placenta appears to be low or over the internal cervical os by transabdominal ultrasound.

Objectives

Three-dimensional ultrasonography offers several additional imaging tools that are not currently provided by more conventional ultrasonography for the detection of vasa previa. It represents an important adjunct to two-dimensional (2D) studies, especially when this diagnosis is questionable.

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Almost all cerebral arteriovenous malformations in the fetus involve the vein of Galen, although occasionally they may involve the frontal area of the brain instead. In all reported cases arteriovenous malformations have presented some time after 30 weeks as a sonolucent oval lesion located in the midline behind the third ventricle. Previous scans have been normal. Evidence of high output failure such as cardiomegaly, enlarged neck veins, or hydrops predicts a poor outcome.

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