Journal of Ultrasound in Medicine, Vol 19, Issue 8 581-585, Copyright © 2000 by American Institute of Ultrasound in Medicine
Clinical significance of placenta previa detected at early routine transvaginal scan
P. Rosati and L. Guariglia
Department of Obstetrics and Gynecology, Catholic University of the Sacred Heart, Rome, Italy.
Transvaginal ultrasonography in early pregnancy was used to determine the
prevalence of placenta previa and the rate of persistence until delivery.
The location of the placenta was registered systematically in 2342 pregnant
women who underwent transvaginal ultrasonography at 10 to 16 weeks'
gestation as a primary examination. The outcome of pregnancy as well as the
presence or absence of placenta previa at delivery was noted in a total of
2158 cases. A receiver operating characteristic curve was generated for the
different measurements from the edge of the placenta to the internal
cervical os versus placenta previa at delivery. In 105 of the 2158 women
screened in the early stages of pregnancy (4.9%) the placenta extended to
or over the internal cervical os, and in 34 of 2158 patients (1.6%) the
distance to the placental edge beyond the internal cervical os was equal to
or greater than 14 mm. Of the eight cases of placenta previa at delivery,
six (75%) were identified in our study, and two cases were missed. When a
cutoff value of greater than 14 mm is used for the receiver operating
characteristic curve the likelihood is 17.6% (95% confidence interval = 6.8
to 34.5) for placenta previa at delivery. Although a high percentage of
false-positive results occur owing to the low prevalence at delivery, this
screening procedure can identify high-risk patients who should be rescanned
later in pregnancy.
