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When Does the Fetal Sac Start to Form and What Causes it to Be Not Yet Apparent?


The fetal sac or gestational sac is an important organ of pregnancy. Examination of the gestational sac is very important to ensure that the mother is carrying the fetus.

Also called gestational sac gestational sac found in the womb. According to family doctor Krissi Danielsson, MD, the gestational sac is one of the first signs of pregnancy that can be seen on an ultrasound. The gestational sac functions to enclose the developing fetus.

“The gestational sac was found in the uterus and contained amniotic fluid,” said Danielsson, quoted from Very Well Family.

“Seeing the gestational sac is indeed a sign that a woman is carrying a fetus, but it is not a guarantee that the pregnancy is healthy and will proceed normally,” he continued.

After the gestational sac is visible, the next positive sign of pregnancy is the yolk sac (yolk bag), which develops in it. The yolk sac provides nutrition for the embryo as it develops until the placenta takes over this task later.

When does the fetal sac start to form?

The fetal sac forms approximately 5 to 7 weeks after the last menstrual period in a regular cycle. However, usually this can be seen via ultrasound between 3 and 5 weeks of pregnancy, Mother.

Please note, the fetal sac can be seen after testing human chorionic gonadotropin (hCG) ranges between 1,500 and 2,000 mIU/mL. However, a 2013 study published in the journal Obstetrics and Gynecology found that the hCG levels that can detect the fetal sac can vary, from 390 to 3,510 mIU/mL.

Meanwhile, in the review at Textbook of Fetal Abnormalities (Second Edition).n) by Peter Twining et al, it is explained that the fetal sac or gestational sac can be identified as early as 4 weeks and 1 day of gestation from the last menstrual period. The diameter of the gestational sac at around 4 weeks of age is around 2 mm and will increase to 5 to 6 mm at 5 weeks of gestation.

“The diameter of the gestational sac increases on average by about one millimeter per day during the first trimester,” according to a review by Peter Twining et al, reported Science Direct.

Another review on National Library of Medicine tahun 2023 explained that the fetal sac is a fluid-filled structure that surrounds the embryo during the first few weeks of embryonic development. The fetal sac is first visible via ultrasound at 4.5 to 5 weeks of gestation, and 97 percent specificity can be used to diagnose intrauterine pregnancy.

Ultrasound illustration/ Photo: iStockphoto/FatCamera

The cause of the fetal sac is not yet apparent

A positive pack test result is indeed a determinant of early pregnancy. However, other important parameters, such as the fetal sac, should not be ruled out.

A positive test pack result does not necessarily mean that the fetal sac has been visible on the ultrasound. There are 5 reasons why the fetal sac is not visible even though the test pack results are positive, namely:

1. The gestational age is still too young

A gestational age that is too young can cause the fetal sac to not be visible even though the pack test results are positive. As previously explained, the gestational sac begins to be detected around 5 weeks of gestation.

At that time, hCG has reached a certain level, Mother. If there is no confirmation regarding hCG levels, then the pregnancy may still be in a very early stage. Mothers need to do a follow-up ultrasound or blood test to confirm pregnancy.

According to reviews in European Journal of Obstetrics & Gynecology and Reproductive Biology In 2018, inappropriate timing is one of the most common reasons the gestational sac cannot be detected on early ultrasound, especially if there are no complaints such as implantation bleeding.

2. Ectopic pregnancy

Ectopic pregnancy can also be a fetal sac that has not been detected on ultrasound. The American Congress of Obstetricians and Gynecologists (ACOG) explains that an ectopic pregnancy occurs when the fertilized egg grows outside the uterus.

“If hCG levels are normal, but the gestational sac is not visible, this may indicate an ectopic pregnancy. However, ACOG says that recording consecutive hCG measurements, taken two to seven days apart to track changes, is necessary for accurate diagnosis,” says Danielsson.

3. Miscarriage

According to ACOG, miscarriage is the loss of pregnancy before 13 weeks. Meanwhile, according to the World Health Organization (WHO), miscarriage is a fetus that dies before 28 weeks of pregnancy.

Most miscarriages are caused by factors that cannot be controlled. Miscarriage can be characterized by abdominal pain and cramps, bleeding, excessive vaginal discharge, and leaking of amniotic fluid.

“If there is a decrease in hCG levels along with no gestational sac being found, the diagnosis is almost certainly a miscarriage. As with ectopic pregnancy, there are different treatment options available if you experience a miscarriage,” says Danielsson.

4. The fetus does not develop

A gestational sac that is not detected on ultrasound could indicate that the fetus is not developing. Usually, the doctor will confirm again by checking the heart rate and length of the fetus.

If the gestational sac has not been detected, the doctor will also carry out further evaluation to ensure that the fetus is not developing. The mother will also be asked to do another ultrasound to determine whether the fetus is developing or not.

5. Errors in using the test pack

The test pack results may be positive or appear vague, but during the ultrasound examination, the fetal sac is not visible. Usually, this happens due to errors in using the test pack, Mother.

There are several errors related to using the test pack that can affect the results being wrong, such as leaving the test pack in the urine for too long, you reading the test pack results too quickly, or the sensitivity of the test pack being low.

What if the fetal sac is empty?

One of the most common types of miscarriage is anembryonic pregnancy, which is when the gestational sac is empty or no embryo is found. This condition can refer to the fetus not developing, Mother.

This type of miscarriage occurs early in pregnancy, and is often not realized by a woman. There are several risk factors for anembryotic pregnancy, namely:

  • Abnormal cell division
  • Chromosomal abnormalities in the fertilized egg
  • Pregnant women experience infections, autoimmune diseases, or endocrine disorders

If the doctor finds an empty fetal sac on an ultrasound examination, they may confirm that the pregnancy cannot be maintained. Anembryotic pregnancy will not result in birth because of its abnormal development.

That is the explanation regarding the fetal sac. Hopefully this information is useful.

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2023-12-25 14:15:02
#fetal #sac #start #form #ultrasound

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