What is the size of the gestational sac in the uterine cavity?

After a woman becomes pregnant, if everything is normal, the fetus will begin to develop in the pregnant woman's body. At this time, a gestational sac will appear and the uterus will also grow as the fetus grows. However, when doing prenatal check-ups, some pregnant women said that their test results clearly showed that their gestational sac was small, so they didn’t quite understand what the problem was. So, what is the size of the gestational sac in the uterine cavity?

Small gestational sac

Firstly, due to emotional tension and other reasons, pregnant women's menstruation is delayed, ovulation is delayed, and conception time is late, resulting in a gestational sac that is smaller than the actual number of days of amenorrhea. For example, the menstruation has not stopped for 50 days, but the examination finds that the gestational sac is only about the size of a 40-day gestational sac. It is normal for the gestational sac to be small. As long as a dynamic examination after one week shows that the levels of chorionic gonadotropin and progesterone are gradually increasing, the gestational sac is continuing to grow, and the fetal bud and fetal heartbeat gradually appear, it means that the small gestational sac is due to physiological reasons such as delayed ovulation and late conception, and the pregnancy can continue.

Secondly, due to poor development of sperm and eggs, infection of mycoplasma, chlamydia, rubella virus in pregnant women, or exposure to toxic and harmful substances during pregnancy, the gestational sac may be poorly developed and smaller than normal. For pregnant women who experience the above situation, the gestational sac will continue to grow as time goes by during pregnancy, but no fetal bud or fetal heartbeat can be seen. In this case, the gestational sac is unhealthy and will eventually lead to miscarriage.

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, and 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.