To evaluate the usefulness of serial transvaginal ultrasonographic measurement of the thickness of the lower uterine segment in the late second trimester for predicting the risk of intrapartum incomplete uterine rupture in women with previous cesarean delivery.
Serial transvaginal ultrasonography with full bladder was performed in 374 women without previous cesarean delivery (control group) and 348 women with previous cesarean delivery (cesarean group) from 19 to 39 weeks' gestation. The thickness of the lower uterine segment was measured in the longitudinal plane of the cervical canal.
The thickness of the lower uterine segment decreased from 6.7 ± 2.4 mm (mean ± standard deviation [SD]) at 19 weeks' gestation to 3.0 ± 0.7 mm at 39 weeks' gestation in the control group, but the thickness was more than 2.0 mm throughout this period in each control subject. In the cesarean group, the thickness decreased from 6.8 ± 2.3 mm at 19 weeks' to 2.1 ± 0.7 mm at 39 weeks' gestation and was significantly thinner than that of the control group after 27 weeks' gestation (P < .05). Eleven of 12 women (91%) with lower uterine segment less than the mean control − 1 SD in the late second trimester had a very thin lower uterine segment at cesarean delivery with fetal hair being visible through the amniotic membrane, ie, incomplete uterine rupture. In 17 of 23 women (74%) with lower uterine segment less than 2.0 mm in thickness within 1 week (4 ± 3 days) before repeat cesarean delivery, intrapartum incomplete uterine rupture developed.
Transvaginal ultrasonography is useful for measurement of the uterine wall after previous cesarean delivery.