How long does it take for a gestational sac to form?

The gestational sac is the first thing that is detected through B-ultrasound in the early stages of pregnancy. The gestational sac contains a yolk sac. Many friends are curious about how long it takes for a gestational sac to form during pregnancy and how to detect it through B-ultrasound. Next, I will introduce it to you in detail. If there are female friends who are interested, please read the content patiently. I would like to remind my friends to take folic acid orally in the early stages of pregnancy to prevent neural tube defects in children.

The gestational sac is only seen in early pregnancy. For women who have regular menstruation of 28 to 30 days, after 35 days of amenorrhea, the gestational sac can be seen in the uterine cavity by B-ultrasound. The diameter of the gestational sac is about 2 cm at 6 weeks of pregnancy and about 5 cm at 10 weeks of pregnancy. It is normal for the gestational sac to be located at the fundus, front wall, back wall, upper part, or middle part of the uterus; it is normal for it to be round, oval, and clear in shape; if the gestational sac is irregular in shape, blurred, and located in the lower part, and the pregnant woman also has abdominal pain or vaginal bleeding, she may have a miscarriage. The gestational sac is the primitive placental tissue, a small embryo wrapped by the amniotic membrane and vascular network. The gestational sac is the initial form of pregnancy. At that time, the fetus has not yet formed, and the fetal heartbeat is already there when the embryonic bud appears. In the second week, the embryo implants in the endometrium. When it develops into the second germ layer, a large cavity called the primary yolk sac appears on the ventral side of the embryonic disc. The yolk sac continues to shrink and degenerate during embryonic development, but the extraembryonic mesoderm on the wall of the yolk sac is the earliest origin of the formation of blood cells, blood vessels and primitive germ cells - the gestational sac, where the fetus will grow in the future.

Size changes

Pregnancy is a complex process. After the egg is fertilized, it enters the uterine cavity, and the embryo and its appendages grow and develop rapidly until they mature. There will be different changes in each week of pregnancy.

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.

5 weeks: The fetus grows to 0.4 cm and enters the embryonic period. The amniotic cavity expands and primitive cardiovascular system appears, which may beat. B-ultrasound can show a small gestational sac, which occupies less than 1/4 of the uterine cavity, or a fetal bud can be seen.

6 weeks: The fetus grows to 0.85 cm. The head, brain alveoli, facial organs, respiratory, digestive, and nervous organs are differentiated. The fetal sac is clearly visible on B-ultrasound, and the fetal bud and fetal heartbeat are seen.

7 weeks: The fetus grows to 1.33 cm. The embryo has the rudiments of a human being. The body segments are fully differentiated, the limbs are separated, and various systems are further developed. B-ultrasound clearly shows the embryo and fetal heartbeat, and the gestational sac occupies about 1/3 of the uterine cavity.

8 weeks: The fetus grows to 1.66 cm. The fetal shape is determined, and the head, body and limbs can be distinguished. The head is larger than the trunk. B-ultrasound shows that the gestational sac occupies about 1/2 of the uterine cavity, the fetal shape and fetal movement are clearly visible, and the yolk sac can be seen.

9 weeks: The fetus grows to 2.15 cm. The head is larger than the body, the various parts are clearer, the skull begins to calcify, and the placenta begins to develop. B-ultrasound shows that the gestational sac almost fills the uterine cavity, the fetal outline is clearer, and the placenta begins to appear.

10 weeks: The fetus grows to 2.83 cm, all fetal organs have been formed, and the rudiments of the placenta are formed. B-ultrasound shows that the gestational sac begins to disappear, a crescent-shaped placenta is visible, and the fetus is active in the amniotic fluid.

11 weeks: The fetus grows to 3.62 cm, the fetal organs develop further, and the placenta develops. B-ultrasound showed that the gestational sac had completely disappeared and the placenta was clearly visible.