You took a home pregnancy test and it came back positive. Although these tests are highly accurate, pregnancy must be confirmed through a blood test measuring human chorionic gonadotropin (hCG) and an ultrasound scan.

During this first ultrasound, your doctor may discuss the presence or absence of the gestational sac. What exactly is the gestational sac? When can it first be detected? What does it mean if it is present or absent? And what if it appears to be “empty”? Here are the answers.

The gestational sac is one of the earliest ultrasound signs of pregnancy. Located inside the uterus, it surrounds the developing embryo and contains amniotic fluid. It can be seen on a transvaginal ultrasound between 3 and 5 weeks of gestation, usually when hCG levels range between 1,500 and 2,000 mIU/mL. Some studies report broader ranges, between 390 and 3,150 mIU/mL. The visualization of the gestational sac confirms pregnancy, but it does not guarantee that it is healthy or evolving normally.

The next reassuring sign is the appearance of the yolk sac inside the gestational sac. The yolk sac nourishes the embryo until the placenta takes over this function. It typically becomes visible between 5.5 and 6 weeks of gestation. However, there are cases in which the gestational sac is seen, but the yolk sac is not detected later.

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What does it mean if the gestational sac is not seen?

There are several possibilities. One is that it is simply too early to visualize it, in which case the ultrasound needs to be repeated. Another possibility is an ectopic pregnancy. If the sac is not visible and hCG levels are decreasing, this may indicate an early miscarriage.

What does an “empty” gestational sac mean?

If the sac is visible but does not contain an embryo, this suggests an anembryonic pregnancy, a type of early miscarriage that often occurs before a woman even knows she is pregnant. Risk factors include:

• abnormal cell division
• chromosomal abnormalities
• infections
• autoimmune conditions
• endocrine disorders

If an empty gestational sac is identified, the doctor may confirm that the pregnancy is nonviable. Depending on the sac’s size, it may be too early for a definitive diagnosis, and a repeat ultrasound may be required.

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The Gestational Sac

If you have questions related to the gestational sac or would like recommendations on evaluating and monitoring your newborn during the first days of life, you may request an individual consultation at any time. A thorough assessment helps determine the most suitable monitoring and support plan for your child.

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