Ultrasound visualization of the human yolk sac

Abstract

Ultrasound scanning in early pregnancy sometimes reveals a 2-5 mm spheric structure lying adjacent to the fetus. The occurrence of this structure was studied in 60 consecutive ultrasound examinations. In the 7th to 9th weeks the sphere was seen in 19 of 22 examinations, and in the 10th and 11th weeks it was seen in 10 of 20 examinations. The sphere was not demonstrated in any of 18 examinations in the 12th to 14th weeks. It is believed that the spheric structure is the yolk sac.