Third-trimester transvaginal ultrasonography in placenta previa: does the shape of the lower placental edge predict clinical outcome?

OBJECTIVE: To evaluate the clinical significance of the shape of the lower placental edge in women with transvaginal sonographic diagnosis of placenta previa.
DESIGN: A prospective observational study at a tertiary teaching hospital. POPULATION: A total of 104 women with confirmed transvaginal sonographic diagnosis of placenta previa before 32 weeks' gestation.
METHODS: Initial transvaginal sonography was performed at between 28 and 32 weeks' gestation in 138 patients with either strong clinical suspicion or previous abdominal sonographic diagnosis of placenta previa in the early third trimester. The lower placental edge was found to be positioned over the internal cervical os in 33 women (complete previa) and within 3 cm from it in 71 women (low-lying placenta). Patients with low-lying placenta were followed up by serial transvaginal sonographic examinations until delivery; detailed information including the placental location (anterior or posterior), the distance of its edge from the internal cervical os and its thickness were recorded. The clinical outcomes of the 17 who had a thick-edge low-lying placenta were compared with those who had a thin-edge one (54 women). In patients with complete placenta previa, demographic data, the shape of the lower placental edge whenever transvaginal sonography visualized it, and the clinical outcomes were documented. The incidence of major complications in thick-edge or central placenta was compared to that in the thin-edge group.
RESULTS: Women having a low-lying placenta with a thick edge had a significantly higher rate of antepartum hemorrhage (P = 0.0002), abdominal delivery (P = 0.02), abnormally adherent placenta (P = 0.012) and low birth weight (P = 0.006) than those in whom the placental edge was thin. Cesarean hysterectomy was required in six patients with complete placenta previa because of severe peripartum hemorrhage; all of them had either central or thick-edge placenta accreta.
CONCLUSION: Women with placenta previa are at a relatively higher risk of developing complications if the lower placental edge is thick. Integration of the shape of the lower placental edge into transvaginal sonographic assessment of placenta previa may improve the prediction of mode of delivery and clinical outcome.