Twin gestation in one horn of a bicornuate uterus.

We report a rare case of twin pregnancy in the same horn of a bicornuate uterus. This patient's uterine malformation was detected for the first time when she experienced abdominal pain at 6 weeks of amenorrhea. Transabdominal and transvaginal sonographic examinations were performed. Both embryos showed cardiac motion on transvaginal sonography. The patient was re-examined monthly. Her pregnancy ended in spontaneous abortion at 22 weeks. Two live male fetuses were delivered, but they both died immediately after their birth. Sonography, particularly transvaginal sonography, is valuable for early detection of uterine abnormalities that may affect the outcome of pregnancy.