Gestational Sac during Pregnancy

Gestational Sac During Pregnancy- What It Indicates

Medically Reviewed By
Dr. Rima Sonpal (Gynecologist/Obstetrician)
View more Gynecologist/Obstetrician Our Panel of Experts

Pregnancy can progress differently for every woman. The conception of a baby can be a complex process. The initial phase of foetal development normally forms the basis for a safe and healthy pregnancy. So, the confirmation of pregnancy is usually followed up by conducting an ultrasound and some blood tests. Your doctor may check the levels of hCG (Human Chorionic Gonadotropin) through a blood test. During an ultrasound, the doctor tries to find the gestational sac, which helps him to ascertain the progress of the pregnancy.

The presence of a gestational sac by three to five weeks of gestation is normally considered a positive mark. It could also happen that a gestational sac is detected but without the presence of an embryo.

In some cases, during the ultrasound, the doctor is unable to see a gestational sac. Such a scenario can arise due to miscalculation of gestational dates, which means it may be too soon to see a gestational sac. But if no gestational sac is spotted even during the follow-ups, it may indicate a possible ectopic pregnancy or a miscarriage.

What is a Gestational Sac?

The detection of a gestational sac through an early ultrasound is usually the easiest way to gauge the advancement of pregnancy. The gestational sac, which is the cavity containing the yolk sac that surrounds the developing embryo, is usually present in the uterus. It looks like a dark space with a white rim around when seen on an obstetric ultrasound.

A gestational sac is the only structural evidence available that may indicate the existence of an intrauterine pregnancy until an embryo can be detected. It usually develops about 5 to 7 weeks after the end of the last menstrual cycle. It is normally noticeable by three to five weeks of gestation when the MSD (Mean Sac Diameter) measures about two to three mm in diameter by obstetric ultrasonography or when the HCG levels are around 1500 to 2000.

The shape of the gestational sac during initial days of pregnancy (before eight to ten weeks) is normally important. Although a round-shaped gestational sac is usually considered ideal, there is no definite way of defining what other shapes mean. But in case the doctor finds the gestational sac to be unusually shaped, he may like to monitor it regularly to rule out any probable complications. Preferably, after 1 or 2 weeks of the last examination of the gestational sac, the doctor should be able to detect the fetal heartbeat, which is a sure shot sign that pregnancy is advancing well.

If a Gestational Sac is Seen On Your Ultrasound, is It a Guarantee of a Normal Pregnancy?

Discovery of a gestational sac during an ultrasound is surely a positive pregnancy sign. However, the presence of a gestational sac alone may not guarantee a normal pregnancy. Apart from the gestational sac, it is important that a yolk sac, which forms within it, also gets developed. The yolk sac is vital, as the developing embryo draws its nutrition from it till the placenta doesn’t take over. The yolk sac normally becomes apparent by 5 to 6 weeks of gestation on a transvaginal ultrasound. Sometimes, a yolk sac is not found, even though a gestational sac may be visible on ultrasound.

Reasons for Absence of a Gestational Sac

The absence of gestational sac may be due to the following reasons:

  • The most common reason can be a miscalculation of gestation. You may have to go for another follow-up ultrasound test. Comparing your hCG levels with the results of your ultrasound test can prove helpful here. If your hCG levels are less than 1500, then it may be too early to look for a gestational sac.
  • A miscarriage has taken place or is likely to happen. Dropping hCG levels may be an indication of a miscarriage.
  • If a gestational sac is not visible and the hCG levels are around 1500 to 2000, it may be a sign of an ectopic pregnancy. Ectopic pregnancy or extra-uterine pregnancy means the embryo gets implanted outside the uterus. Such an occurrence is a medical emergency and may require further testing for proper diagnosis and treatment. Serial monitoring of BhCG levels is suggested in this case.


What Does an Empty Gestational Sac Indicate?

It is possible to detect an embryo in the gestational sac in six weeks of gestation. However, sometimes, an anembryonic pregnancy or gestational sac miscarriage may occur. In such an instance, the early gestational sac is empty and does not hold an embryo. It simply means that an embryo was unable to develop. The reasons can range from abnormal cell division to poor quality egg or sperm. Such a pregnancy loss normally happens during the initial days of pregnancy and often without a woman even realizing that she was pregnant.

In many cases, a woman undergoes natural miscarriage without intervention due to chromosomal irregularities, while in some cases a woman may have to opt for a D&C (Dilation and Curettage) procedure.

What Your Doctor Will Do if He Sees an Empty Gestational Sac

An empty gestational sac can be because of reasons like early intrauterine pregnancy, anembryonic pregnancy or blighted ovum. In case your doctor notices an empty gestational sac, he may test your hCG levels and suggest another ultrasound, as sometimes it can be difficult to calculate the gestational age that early in pregnancy and the follow-up ultrasound tests may reveal an embryo later on.

However, if the results are unfavourable, he may prepare you for a miscarriage, as the pregnancy is not advancing normally and is not likely to result in the birth of a child. The doctor may also declare a pregnancy non-viable (failed pregnancy) if he observes an irregular gestational sac, which simply means that the gestational sac does not possess the well-defined, consistent structure of a normal gestational sac.

Different women can have varied pregnancy experiences. It is important to remain stress-free and enjoy your pregnancy as much as possible. You can always seek emotional and physical support from family and friends. It is sensible to consult your doctor for the necessary guidance and treatment in case of any complications.

Also Read: Pregnancy Complications To Watch Out For

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