Facts About Gestational Sac That Mothers Should Know

Gestational Sac Facts That Mothers Should Know

The gestational sac is the uterine sac that surrounds and protects the embryo during pregnancy. Learn the facts about the gestational sac here.

After taking a pregnancy test that shows a positive result or a blood test measuring human chorionic gonadotropin (hCG) levels indicating pregnancy, the next step is to undergo an ultrasound examination at the hospital for accurate confirmation of the pregnancy.

During the first ultrasound examination, the doctor may discuss the presence or absence of the gestational sac. So, what is the gestational sac exactly? When is it first detected on an ultrasound? Find out the answers here.

What Is the Gestational Sac?

According to the National Library of Medicine, one of the first signs visible on an ultrasound examination is the gestational sac. The gestational sac protects the developing fetus and contains amniotic fluid. It is located inside the uterus and appears as a transparent, circular white shape.

To visualize the gestational sac, the doctor will recommend a transvaginal ultrasonography test. Transvaginal ultrasonography has a higher sensitivity and produces clearer images compared to transabdominal ultrasonography.

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The gestational sac is typically visible when your hCG levels are between 1,500 and 2,000 mIU/mL. However, a study in 2013 found that the hCG levels that can detect the gestational sac can vary significantly, ranging from 390 to 3,510 mIU/mL.

When Is the Gestational Sac Visible on an Ultrasound Examination?

The gestational sac usually forms around 5 to 7 weeks after the last menstrual period in a natural cycle, so it is typically visible between 3 to 5 weeks of gestation using transvaginal ultrasound.

Once the gestational sac is visible, the next positive sign of pregnancy is the presence of the yolk sac developing within it. The yolk sac provides nutrients to the developing embryo until the placenta takes over. This is an important indicator of a healthy pregnancy.

In some cases, although the gestational sac can be detected through ultrasonography, the yolk sac may not be clearly visible. The yolk sac is typically visible on transvaginal ultrasonography at around 5 to 6 weeks of gestation.

In addition to the gestational sac and yolk sac, at around 6 weeks of gestation, you will also see the fetal pole (early embryonic stage). The fetal pole appears as a line or oval-shaped structure near the yolk sac, measuring about 1 to 2 millimeters.

At this stage, the fetal pole does not yet have distinct features but begins to take shape around 7 to 8 weeks of gestation when the spinal cord starts to form.

What If the Gestational Sac Is Not Visible?

Typically, when a woman has a positive pregnancy test result, the gestational sac will form. However, if the gestational sac is not visible between 4.5 to 5 weeks of gestation, there are several conditions to consider.

Early ultrasound examination: Errors in calculating gestational age can lead to the gestational sac not being visible. Your obstetrician will observe for several more weeks and may recommend a repeat ultrasound examination.

Ectopic pregnancy can occur if the gestational sac is not visible, and hCG hormone levels remain normal. This indicates that the embryo is implanted and developing outside the uterine cavity, such as in the fallopian tube, ovary, cervix, or abdominal cavity.

Chemical pregnancy can occur if the gestational sac is visible, but hCG hormone levels decline. This indicates a pregnancy loss at less than 5 weeks of gestation.

The Gestational Sac Does Not Contain an Embryo

The presence of the gestational sac does not automatically guarantee a healthy and normal pregnancy. In rare cases, pregnant women may experience anembryonic pregnancy or a blighted ovum, where the gestational sac does not contain an embryo. In other words, the embryo has failed to develop or the woman has experienced a miscarriage.

This type of miscarriage usually occurs in the early first trimester and often before someone realizes they are pregnant. Risk factors for anembryonic pregnancy include abnormal cell division, chromosomal abnormalities in the fertilized egg, infections, autoimmune diseases, or endocrine disorders in the pregnant woman.

In many cases, chromosomal abnormalities will cause the body to naturally miscarry without intervention. However, in some situations, pregnant women experiencing a miscarriage may need to undergo dilation and curettage (D&C) procedures to remove the tissue from the uterus.

This procedure may be necessary to identify the cause of the miscarriage through pathological examination, and it can also help the mother identify or be more cautious in managing future pregnancies. Additionally, there are medical management options for miscarriage involving the use of medication to help the body expel the non-developing pregnancy.

Those are the explanations and facts about the gestational sac. For more information about infertility, read other articles on the Bocah Indonesia website.


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  • Cleveland Clinic. Diakses 2023. Yolk Sac
  • Very Well. Diakses 2023. Gestational Sac and Its Meaning in Pregnancy
  • Science Direct. Diakses 2023. Gestational Sac
  • https://www.ncbi.nlm.nih.gov/books/NBK551624/
  • https://www.ncbi.nlm.nih.gov/books/NBK555965/
  • https://pubmed.ncbi.nlm.nih.gov/12230450/

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