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Empty Gestational Sac Medically Reviewed

Last Updated: June 10, 2020

Definition - What does Empty Gestational Sac mean?

An empty gestational sac is a cavity within a uterus that forms to house a pregnancy but the embryo has stopped growing.

This means that a fertilized egg was capable of implanting within the uterine wall to signal a pregnancy, but the embryo does not continue to develop and the pregnancy fails to progress. It is an early form of miscarriage.

An empty gestational sac is also referred to as a blighted ovum (considered to be an outdated term) or an anembryonic pregnancy.

FertilitySmarts explains Empty Gestational Sac

In the very early stages of a developing pregnancy, a gestational sac is a fluid-filled structure that encloses a developing embryo. It is also the first visual evidence of pregnancy and can provide information on how a pregnancy is progressing.

A gestational sac can be detected on a transvaginal ultrasound scan when it measures as little as 2-3 mm in diameter at approximately 4.5- 5 weeks. The measurement of the structure can help to estimate gestational age and to assess how a pregnancy is developing.

Mean Sac Diameter

The mean sac diameter (MSD) is a measurement of the gestational sac that can provide information about the development and viability of an embryo. This is done by measuring the length, width, and height of the sac and dividing it by 3.

When is a gestational sac considered empty?

A gestational sac is labeled as being "empty" when it approaches a MSD of 25 mm and a transvaginal ultrasound fails to identify a fetal pole/embryo.

This means that the pregnancy is not viable and will end on its own through a spontaneous miscarriage.

When does an empty gestational sac occur?

Gestational Sac at 7 weeks

  • A fetal pole inside of a gestational sac with a crown-to-rump length greater than 7mm at around 7 weeks should have fetal cardiac activity.

Gestational sac at 8 weeks

  • The fetal pole should be visualized when the MSD of the gestational sac is at least 25mm, which typically occurs at the end of 7 weeks or early week 8.
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