To analyze the ultrasonographic features of conjoined twins and summarize the diagnostic skills in early pregnancy.

The ultrasonographic features, sites of union, type of fusion, related abnormalities and pregnancy outcomes were analyzed in 21 cases of conjoined twins who were checked up for early vagina bleeding during the first trimester or for 11^th-13^{th+ 6} gestational week scanning between January 2011 and December 2017 Shenzhen Maternity and Child Healthcare Hospital. The diagnostic skills of conjoined twins in early pregnancy were summarized.

Twenty-one cases of conjoined twins were diagnosed in the first trimester, whose gestational age were estimated by crown-rump length. NT measurements were obtained in 8 cases, of which 7 cases had increased nuchal translucency over 3.0 mm. The prenatal ultrasonic results of conjoined twins: there were 12 cases (12/21) of thoraco-omphalopagus, 3 cases (3/21) of cephalopagus, 3 cases (3/21) of parapagus dicephalus, 2 cases (2/21) of omphalopagus and 1 case (1/21) of ischiopagus. All cases were associated with other anomalies, including rachis deformation, single cardiac ventricle, gastroschisis, diaphragmatic hernia, omphalocele and spina bifida. Three-dimensional ultrasound imaging was helpful to confirm the types of fusion and improve facial features, which could be understood more easily. Postpartum examination showed: four cases had intrauterine fetal death, in the other 17 cases parents chose to terminate the pregnancy after ultrasound examination. All cases were confirmed to be conjoined twins by postpartum specimens.

Ultrasound examination in early pregnancy can make a clear diagnosis of the type of fusion and related abnormalities of conjoined twins, which is conducive to pregnant women for prenatal consultation.