RESUMEN
BACKGROUND: Conjoined twins are a rare occurrence, and the majority of these malformations are detected during second trimester screening. CASE SUMMARY: Herein we report a case of conjoined twins, which was diagnosed by ultrasound at 8 wk gestation and was normal at 7 wk gestation. The two fetuses shared one heart and were diagnosed as thoracopagus twins. This is the first report of conjoined twins diagnosed at 8 wk gestation. The pregnancy was terminated electively at 9 wk gestation. Because some congenital malformations can be diagnosed earlier, a prenatal ultrasound examination at an early gestational stage cannot be dismissed. CONCLUSION: This case demonstrates that a 7-8 wk gestation might be the earliest period when conjoined twins can be diagnosed by ultrasound.