What is the Difference Between Yolk Sac and Gestational Sac?

The yolk sac and gestational sac are two structures that develop during early pregnancy and can be identified through ultrasound. They play crucial roles in the growth and development of the embryo. Here are the differences between the two:

• Appearance: The gestational sac is a fluid-filled structure surrounding the developing embryo, appearing as a round or oval structure with a smooth, circular, and echogenic lining on transvaginal ultrasound. The yolk sac is located inside the gestational sac and appears as a round, hypoechoic structure with surrounding walls that are echogenic.
• Size: The yolk sac is smaller than the gestational sac, with a normal yolk sac size ranging from 3 mm to 5 mm. The gestational sac is larger and can be identified at around 5 weeks of gestation, while the yolk sac becomes visible at approximately 5.5 weeks.
• Function: The gestational sac provides a protective environment for the developing embryo, while the yolk sac attaches to the outside of the developing embryo and provides nutrients, circulates gases between the mother and fetus, and produces cells that turn into important structures.
• Timeline: The gestational sac is the first structure identified in the uterus during early pregnancy, while the yolk sac is the second structure identified.

Both the gestational sac and yolk sac are essential for the healthy development of the embryo, and any abnormalities in their size, shape, or appearance can be indicative of pregnancy complications or failure. Healthcare providers use ultrasound to monitor these structures and assess the health of the pregnancy.

Comparative Table: Yolk Sac vs Gestational Sac

Here is a table comparing the differences between the yolk sac and the gestational sac:

The yolk sac is the second structure identified in the uterus during early pregnancy, visible at around 5.5 weeks. It provides nourishment to the embryo and helps circulate gases between the mother and the embryo. The yolk sac also produces cells that turn into important structures such as the umbilical cord, blood cells, and reproductive organs. On the other hand, the gestational sac is the first structure identified in the uterus during early pregnancy, visible at around 5 weeks. It confirms early pregnancy through ultrasound and is larger than the yolk sac. The majority of yolk sacs decrease in size before disappearing at around 12 weeks of gestation.