How many months of pregnancy does the placenta grow

The placenta begins to form slowly during the fourth week of the mother's pregnancy. The placenta, which is the endometrium of the uterus, is slowly formed. The placenta can be seen around the tenth week of pregnancy. Before that, it is relatively important. You cannot have sex during this period. Pregnant women should pay attention to getting enough rest, strengthening their diet, and paying attention to a balanced diet. Only in this way can they promote the good development of the fetus.

What are the functions of the placenta?

1. Nutritional effect: Glucose, amino acids, vitamins, electrolytes, etc. required for fetal growth and development can be transported to the fetal blood through the placenta. At the same time, the placenta produces various enzymes that can decompose complex substances into simple substances, or synthesize simple substances into glycogen, protein, cholesterol, etc., and supply them to the fetus.

2. Gas exchange: The oxygen pressure of maternal blood is higher than that of umbilical cord blood, and can enter the fetal blood circulation through the villi by diffusion. Carbon dioxide can dissolve in the fetal membrane and is easily exchanged without the need for significant differences in gas partial pressure.

Human chorionic gonadotropin (hCG) is a glycoprotein hormone whose origin is not yet clear, but its secretion amount roughly parallels the development and regression of Langerhans cells. It appears in the urine 20 days after fertilization, that is, on the 35th day of pregnancy. The concentration increases to the 45th day of pregnancy, reaches the highest concentration at the 60th day, and then gradually decreases to the lowest level at the 18th week of pregnancy, maintaining it until delivery and disappearing about 4 days after delivery. Its main function is to allow the corpus luteum to develop into the corpus luteum of pregnancy to maintain pregnancy until the placenta functions to secrete enough steroid hormones to replace the secretion of the ovaries. It can also stimulate the gonadal activity of female and male animals. It is used clinically to diagnose early pregnancy.

5. The structure of the immune function placenta prevents direct blood flow between mother and child, thus eliminating the necessary conditions for the first rejection. In the late pregnancy, there is a layer of fibrin-like deposits between the placenta and the mother, and the trophoblast cells are surrounded by a layer of fibrous substances composed of hyaluronic acid and sialic acid, which may form a barrier to block cell antigens. In addition, steroid hormones and protein hormones produced by the placenta may also have a certain immunosuppressive effect. 6. Defensive effect: Generally, bacteria and larger pathogens cannot pass through the placenta, but viruses can enter the fetal blood through the placenta. Certain pathogens such as Mycobacterium tuberculosis, Plasmodium, and Treponema pallidum can first form lesions in the placenta, destroy the villi, and then enter the fetal blood to infect the fetus. Antibodies in the mother's blood can also pass through the placenta into the fetal blood, giving the fetus passive immunity. However, the mother's anti-A, anti-B, anti-Rh and other blood type antibodies also enter the fetal blood, causing fetal hemolysis and stillbirth. Certain drugs, such as barbiturates, morphine, chlorpromazine, ether, antibiotics, quinine, arsenic agents, etc., can enter the fetus through the placenta, so pregnant women should consider the impact on the fetus when taking drugs.