Purpose: Explore the ultrasound characteristics of thoracoabdominal conjoined twins in early pregnancy, summarize the key points and techniques of ultrasound diagnosis of thoracoabdominal conjoined twins in early pregnancy.Methods: A retrospective analysis of 7 cases diagnosed as thoracoabdominal conjoined twins by ultrasound before 13+6 weeks of pregnancy in our hospital from 2010 to 2022 and confirmed by induced abortion. The ultrasound characteristics of thoracoabdominal conjoined twins were observed, and the consistency between ultrasound findings and post-abortion external appearance was compared. Summarize the key points and techniques of ultrasound diagnosis of thoracoabdominal conjoined twins in early pregnancy.Results: In early pregnancy, thoracoabdominal conjoined twins can be seen with a forked appearance in the sagittal section and it may be difficult to obtain a standard sagittal section. Incisions can be seen at the fetal body junction in the transverse section of the thoracoabdominal area, presenting a "∞" sign.Both twins in the thoracoabdominal conjoined twins only have one rhythm of heart beating, and the position is central. All 7 cases of conjoined twins chose induced abortion, and the post-abortion external appearance was consistent with the prenatal diagnosis.Conclusion: The definitive diagnosis of thoracoabdominal conjoined twins in early pregnancy is of great significance. Thoracoabdominal conjoined twins can be easily missed in early pregnancy, with characteristic features such as a forked appearance in the sagittal section, a "∞" sign at the junction of the thoracoabdominal walls in the transverse section, and the presence of only one rhythm of heartbeats helping to confirm the diagnosis of thoracoabdominal conjoined twins.