Gestational sac: What it is, what size and common problems

Gestational sac is the first structure formed at the beginning of pregnancy and it functions to shelter the baby as well as forming the placenta and the amniotic sac, so that the baby can grow healthily, and be present until approximately the 12th week of gestation.

The gestational sac can be visualized using a transviganal ultrasound around the 4th week of gestation and it is located in the central part of the uterus, measuring about 2 to 3 mm in diameter; a great parameter for confirming the presence of pregnancy. However, at this stage it is still impossible to visualize the baby as it will appear in the gestational sac after about 4.5 to 5 weeks of gestation. For this reason, doctors prefer to wait until the 8th week to perform ultrasound so as to have a safer assessment of how the pregnancy is developing.

Gestational sac evaluation is a good parameter to verify whether pregnancy is developing as it should. The parameters that are usually evaluated by the physician include size, shape and contents of the gestational sac.

Gestational bag size table

The gestational sac increases in size with the development of pregnancy. During ultrasound, the doctor evaluates the results of this test using the following table:

The reference values of the gestational sac size table allow the physician to identify problems and anomalies of the gestational sac in advance.

Most common problems with gestational sac

A healthy gestational sac is regular in shape with symmetrical contours and good implantation. When there are irregularities and low implantation, the chances of pregnancy not developing properly are increased.

The most common problems include:

Empty gestational bag

After the 6th week of pregnancy, if the foetus is not observed by ultrasound, it means that the gestational sac may be empty and therefore it means the embryo did not develop after fertilization. This type of pregnancy is referred to as an embryonic pregnancy or blind egg.

The main causes of foetus not developing is due to abnormal cell division and poor quality sperm or egg. Generally, in such a case, the doctor may request to repeat the ultrasound after the 8th week to confirm the embryonic pregnancy. If it is confirmed, the doctor may wait for a few days in case of a miscarriage, and hospitalisation may be required.

Displacement of the gestational sac

The displacement of the gestational sac may occur due to the growth of a hematoma in the gestational sac. This may be as a result of physical exertion, a fall or hormonal changes like dysregulation of progesterone, high blood pressure, consumption of alcohol and drug abuse.

Signs of displacement are usually a mild or intense colic and brown or bright red bleeding. Generally, when the displacement is greater that 50%, chances of miscarriage are high. There is no effective way to prevent the displacement, but in case it occurs, the doctor will prescribe medications and recommend absolute rest for at least 15 days. In more severe cases, hospitalization may be required.

When to go to the doctor

It is advisable to go to the doctor if the symptoms of severe colic or bleeding are experienced, and this cases one should immediately seek maternal or emergency care and contact the doctor to monitor the pregnancy. The diagnosis of problems related to the gestational sac can only be made by the doctor using ultrasound and for this reason it is important to start prenatal care as soon as pregnancy is known.