Examination of the second-trimester fetus with severe oligohydramnios using transvaginal scanning.

Transvaginal sonographic transducers have permitted better resolution of the pelvic structures than previously possible. The presenting fetal part may be difficult to image transabdominally when lodged deep in the lower uterine segment. In particular, second-trimester fetuses associated with severe oligohydramnios present a challenge to the sonologist because of both the lack of amniotic fluid and the deep and curled fetal position in the maternal pelvis. Two cases are reported of second-trimester oligohydramnios in which the fetal abnormalities were visible only with the vaginal probe. The vaginal scan permitted a definitive diagnosis of Potter syndrome not possible with the poorer resolution of the transabdominal approach. I conclude that transvaginal scanning should be considered in patients with unexplained severe oligohydramnios because the resolution of the fetal anatomy is greatly enhanced.