Why can't I see the gestational sac on ultrasound?

Pregnant women should all know that the gestational sac is the initial form of fetal growth. Pregnant women will go to the hospital for an ultrasound to check whether the baby is growing healthily. However, if you go to the hospital for a check-up one month after pregnancy, the gestational sac will definitely not be visible through ultrasound. Because in the early stages of pregnancy, the gestational sac may only contain an embryo. Generally speaking, the gestational sac can be seen from B-ultrasound about six weeks after pregnancy, but this varies from person to person. Some people may see the results in a month, while others may not even see them in the sixth week.

The gestational sac is the initial form of pregnancy. It is a small embryo wrapped in the original placental tissue by the amniotic membrane and vascular network.

The fetus had not yet formed at that time, but the fetal heartbeat was already there when the embryo bud appeared. The gestational sac is very small at first and then grows slowly. Generally speaking, after 5 weeks of pregnancy, a small gestational sac can be seen on B-ultrasound, which occupies less than 1/4 of the uterine cavity, or a fetal bud can be seen. If it is a normal intrauterine pregnancy, the gestational sac can be seen in the uterus through B-ultrasound around 40 days of pregnancy. However, due to individual differences in the time of conception, some pregnant women may not be able to see it until around 45 days.

For women who have regular menstruation of 28 to 30 days, after 35 days of amenorrhea, ultrasound can show the gestational sac in the uterine cavity, even though the fetus has not yet formed.

At 4 weeks, the fetus is only 0.2 cm. The amniotic cavity is formed just after the fertilized egg has implanted and its volume is very small. Ultrasound cannot show clear signs of pregnancy. Usually, when hCG reaches 1000U/L, vaginal ultrasound should be able to identify the intrauterine gestational sac. This time is around the 4th or 5th day of the 5th week of pregnancy. When hCG reaches 6500U/L, abdominal ultrasound can identify the intrauterine gestational sac. Therefore, vaginal ultrasound will be more accurate. If the intrauterine gestational sac is not seen on the 49th day of pregnancy during a normal menstrual cycle, ectopic pregnancy should be suspected.

The gestational sac is also considered a product of ectopic pregnancy.

If the fertilized egg fails to enter the uterus at 7 days due to inflammation, adhesion or other factors, ectopic pregnancy will usually result in heavy bleeding and the fetus will generally not survive. The baby's mother herself was having an intrauterine pregnancy, but due to poor development of the uterus, the gestational sac broke through the weak top of the uterus and entered the abdominal cavity. The villi around the gestational sac sought nutrients everywhere in the abdominal cavity and then supplied them to the fetus through the placenta. Usually, such a fetus will die within two months because it has no protection from the uterine environment and lives in an extremely harsh environment with poor nutrition.