The yolk sac is usually the second structure to become visible on ultrasound in early pregnancy, appearing inside the gestational sac shortly before the embryo itself can be seen. Its appearance is a reassuring, though not conclusive, sign that a pregnancy is developing normally within the uterus. An unusually large, small or irregularly shaped yolk sac can sometimes be noted by the sonographer, but on its own it is not used to predict the outcome of a pregnancy; the overall picture, including growth over repeat scans, matters more than any single measurement.
Also known as: yolk sac on scan
Related India guides
Sources
- Federation of Obstetric and Gynaecological Societies of India (fogsi.org)
Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.