Gestational Sac

Definition - What does Gestational Sac mean?

The gestational sac is the structure that encloses the fetus and amniotic fluid in the very early stages of pregnancy. The gestational sac is the first visual evidence of pregnancy, identified via ultrasound in the initial 5-7 weeks of gestation before the embryo is even visible. The presence of a gestational sac may indicate whether or not a healthy pregnancy is developing and indicate if any issues are present.

FertilitySmarts explains Gestational Sac

The gestational sac appears on an ultrasound as a large fluid-filled sphere surrounded by a thin, white ring. It is located in the center of the uterus, called the fundus, and in early pregnancy grows by 1 mm per day. Inside of the gestational sac, a smaller sac called the yolk sac should appear. The yolk sac is responsible for the nourishment of the fetus before the placenta forms. Several situations may indicate concerns regarding the early pregnancy:

  • Empty gestational sac. This occurs when an embryo implants but fails to survive. In this case, the body responds to early pregnancy triggers and the gestational sac is developed, however, there is no longer a fetus growing inside. This early type of miscarriage often goes unnoticed by the woman, as the pregnancy would have existed for such a short period of time.
  • Gestational sac fails to grow, or yolk sac fails to develop. Either condition indicates that the pregnancy is not progressing, and the embryo may not have survived.
  • No gestational sac is visible. Following a positive pregnancy test, a lack of gestational sac may indicate that an ectopic pregnancy is occurring.


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