1.What is a gestational sac? The gestational sac is the initial form of pregnancy, when the fetus has not yet formed and the fetal heart is already beating when the germ appears. The gestational sac is also considered a product of ectopic pregnancy, where the fertilized egg does not enter the uterus at 7 days due to some factors such as inflammation and adhesions, and usually ectopic pregnancies bleed profusely, and generally speaking, the fetus does not survive. 2, the regular size of the gestational sac at different days of pregnancy Pregnancy is a complex process, after the egg is fertilized, it enters the uterine cavity, and the embryo and appendages grow and develop rapidly until maturity, each pregnancy week will have different changes. 4 weeks: The fetus is only 0.2 cm. The fertilized egg has just completed its implantation, the amniotic cavity has only formed and is very small. The ultrasound cannot yet see any signs of pregnancy. 5 weeks: The fetus reaches 0.4 cm and enters the embryonic stage, the amniotic cavity is enlarged, the primitive cardiovascular vessels are present and may be pulsating, and a small fetal sac can be seen on ultrasound, occupying less than 1/4 of the uterine cavity, or a fetal bud may be visible. 6 weeks: The fetus grows to 0.85 cm, the fetal head, brain vesicles, frontal organs, whistling, digestive and neurological organs are differentiated, the fetal sac is clearly visible on ultrasound, and the fetal bud and fetal heartbeat can be seen. The fetus is 1.33 cm long, the embryo is already in human form, all the body segments are differentiated, the limbs are separated, and the systems are further developed. 8 weeks: The fetus is 1.66 cm long, the fetal shape is fixed, the fetal head, body and limbs can be separated, the fetal head is larger than the trunk, the fetal sac is visible on ultrasound, the fetal form and fetal movement are clearly visible. The fetus is clearly visible, and the yolk sac can be seen. The fetal head is larger than the fetal body, and all parts of the fetus are clearer, the cranium is calcified and the placenta is developing. 10 weeks: The fetus is 2.83 cm long, all the fetal organs are formed, the placenta is forming, the ultrasound shows that the fetal sac begins to disappear, the placenta is visible in the shape of a moon bud, the fetus is active in the amniotic fluid. 11 weeks: the fetus grows to 3.62 cm, all the fetal organs are further developed and the placenta is developing. the ultrasound shows that the fetal sac completely disappears and the placenta is clearly visible. 3.What is an empty gestational sac? Empty gestational sac is an embryo that has not developed well for many reasons, such as poor sperm quality and environmental factors that can affect the development of the embryo, and sometimes an empty gestational sac can occur when the fertilized egg is late. The empty gestational sac will usually be a natural abortion. 4.Can a pregnant woman continue to be pregnant with a small gestational sac? Whether the pregnancy can continue or not can only be determined after a week of dynamic observation. In general, a small gestational sac may be due to emotional stress, which leads to delayed menstruation, late ovulation and late conception, resulting in a smaller gestational sac than the actual number of days of menopause. For example, if the menopause is 50 days old, but the test reveals that the gestational sac is only about 40 days old. This kind of small gestational sac is normal, and as long as the chorionic gonadotropin and progesterone values are gradually increasing after one week of dynamic examination, and the gestational sac continues to grow, and the fetal bud and fetal heart gradually appear, it means that the small gestational sac is due to physiological reasons and the pregnancy can continue. If it is due to mycoplasma, chlamydia, rubella virus and other reasons during pregnancy, resulting in the gestational sac being underdeveloped and smaller than the normal month, the gestational sac is unhealthy and will eventually lead to miscarriage, it is best to go to a regular hospital to have the uterus removed, then identify the cause and treat it properly, and get pregnant again after one year. 5.What is the yolk sac? It is a membranous sac with abundant blood vessels located outside the yolk on the ventral side of the embryo. The constricted part of the sac that is connected to the midgut of the embryo is called the yolk sac stalk. The wall of the bursa is composed of an inner layer of extra-embryonic endoderm and an outer layer of extra-embryonic mesoderm. Reptile and bird eggs are rich in yolk, which is large and has the function of storing, breaking down, absorbing and transporting nutrients. The yolk sac gradually shrinks as the embryo grows and the yolk is consumed, eventually being absorbed into the body and fused to form part of the small intestine. Eggs of lower mammals are rich in yolk and have fairly well-developed yolk sacs; eggs of fetal mammals are less yolky and have small yolk sacs that do not contain yolk. At the end of the 5th week, the yolk sac of the human embryo is separated from the primary intestine and gradually degenerates to a small sac less than 5 mm in diameter, which remains on the surface of the placenta by the 7th week. The occurrence of the human embryonic yolk sac is also one of the phenomena of repertoire phylogenesis. The extraembryonic mesoderm on the human yolk sac forms many blood islands in the 3rd week, which are the first sites of blood vessel and blood cell formation in the embryo and are the sites of hematopoiesis in the early embryo (before 10 weeks), and the yolk sac arteries and veins will participate in the formation of mesenteric arteries and hepatic portal veins. The yolk sac is also the initial site of germ cell formation as the primitive germ cells also appear in the wall of the yolk sac. The yolk sac can also be found in other crested animals and mollusk cephalopods. 6. What does the yolk sac represent and at what gestational age can it be seen? To use an analogy, having a yolk sac is the same as having a house built and waiting for someone to live in it. When the yolk sac is visible on ultrasound, it is almost the time when the yolk sac appears, first the yolk sac, then the fetal bud and fetal heart. The presence of the yolk sac indicates that the embryo is ready to develop. In fact, the redness is not a big deal and can be preserved, but I am afraid of those who have no symptoms, no abdominal pain, no redness, no bumps and bruises, and finally go to the hospital to check that the embryo has stopped developing. The most intuitive way to determine whether the embryo is developing and whether it is developing well is to insist on taking the temperature in early pregnancy. If you’re not sure if you’re going to be able to get a good deal on your own, you’ll be able to get a good deal on your own. If you’ve got the right amount of time to play progesterone and progesterone, there’s hope that your baby will be saved. If the temperature keeps dropping even after the luteal injection, it means that the embryo has started to stop developing and it is useless to keep it. Even if the baby is preserved, then the embryo will still develop and there will be the possibility of malformation. Generally, the fetal sac is clearly visible on ultrasound at around 6 weeks, and the fetal bud and heartbeat are visible. If your test results are abnormal, there may be problems with the development of the embryo and you need to talk to your obstetrician further.