What is Rh blood group? There are several classification systems for human blood groups, the most commonly used is the ABO blood group classification, and there is also the Rh blood group classification. Rh factor is a protein that can be found on the surface of red blood cells, most people have Rh factor on the surface of red blood cells, which is called Rh blood group positive, and a few people lack Rh factor on the surface of red blood cells, which is also known as Rh blood group negative. In Europe and the United States, the proportion of Rh-negative people accounts for about 15% of the population. The Rh-negative blood type in the Chinese Wei population is about 5%, and the Rh-negative blood type in Han Chinese is relatively rare, accounting for only about 3/1000 of the population. If both ABO and Rh blood group systems are considered, the chance of finding AB Rh(-) homozygotes in the Han Chinese population is less than three in 10,000. Because of their rarity, Rh-negative blood types are also known as “panda blood types”. How is Rh blood type inherited? The Rh factor depends on the genes of the parents. If the mother’s blood type is Rh-negative and the father’s blood type is Rh-positive, the child’s blood type can be either Rh-positive or Rh-negative. If both parents have Rh-negative blood types, the child’s blood type will be Rh-negative, not Rh-positive. Problems faced by Rh-negative pregnant women Problems of the mother herself: Because of the rare blood type, the blood supply will be tight in case of heavy bleeding during the delivery period. The number of Rh-negative blood in stock at the blood bank is usually low, and since the ABO blood type match is also taken into account, there will be even less to choose from. Therefore, for Rh-negative pregnant women who are at risk of hemorrhage, it is important to prepare a plan for blood preparation in advance. Adverse effects on the fetus: For Rh-negative mothers, if the child is Rh-negative, there is no problem, but if the child is Rh-positive, it is called “Rh blood group incompatibility”. If the blood of an Rh-positive fetus enters the body of an Rh-negative pregnant woman, it will stimulate her body to produce antibodies against the Rh factor, resulting in “Rh sensitization” of the pregnant woman. “Rh incompatibility has no effect on the first child because the child is born before the mother has developed enough antibodies in her body. If precautions are not taken during the first pregnancy, the mother’s body will produce many antibodies against the Rh factor, and if the fetus is still Rh-positive during the next pregnancy, it will be prone to more serious consequences. What are the conditions under which antibodies are produced in Rh-negative pregnant women? Normally, the blood circulation of the mother and the fetus is relatively isolated from each other, but it is possible for a small amount of fetal blood to enter the mother’s bloodstream during pregnancy and delivery. In addition to the delivery process, fetal blood may enter the mother’s system in some cases such as amniocentesis, chorionic villus biopsy, bleeding during pregnancy, external inversion of the breech position, and impact injuries to the abdomen during pregnancy. Not only can a full-term pregnancy lead to sensitization of the Rh-negative mother, but if the embryo is Rh-positive, the mother’s body may still produce Rh antibodies even after a spontaneous abortion, an ectopic pregnancy, or an induced abortion. How does intrauterine hemolysis occur? If an Rh-sensitized mother becomes pregnant again, the Rh antibodies in her body will cross the placenta into the Rh-positive fetus and attack the fetus’ red blood cells, causing destruction of the red blood cells. As the destruction of red blood cells increases, the fetus will develop varying degrees of hemolysis, leading to hemolytic anemia. As the hematocrit level decreases, the fetus may develop local or generalized rows of edema, and in severe cases, fetal heart failure or even death. How is the fetus monitored? The first step is to examine the mother for Rh antibodies in her peripheral blood and to monitor the level of antibodies regularly. Secondly, ultrasound is used to detect the presence of intrauterine hemolysis and to determine the extent of intrauterine hemolysis. The main indicators of ultrasound are the changes in blood flow in the middle cerebral artery and the edema of the fetus, as well as the thickening and edema of the placenta. How to prevent Rh sensitization? For Rh-negative pregnant women, Rh immunoglobulin (RhoGAM) can be injected to prevent the production of Rh antibodies so that the next pregnancy with an Rh-positive fetus will not have hemolysis caused by an antigen-antibody reaction. However, if antibodies have already been produced, Rh immunoglobulin injections will not be useful, so the key is prevention. When to give Rh immunoglobulin? For Rh-negative pregnant women, Rh immunoglobulin injections are required in the following cases: 1. at 28 weeks of gestation to prevent the occurrence of sensitization 2. In case of delivery of an Rh-positive child, the injection needs to be given within 72 hours. 3. Injected after spontaneous abortion, induced abortion, or ectopic pregnancy. 4. Injection after amniocentesis, chorionic villus biopsy. What should I do if the mother is Rh-sensitized and the fetus is Rh-positive? In addition to regular antibody tests, ultrasonography is needed to determine if there is intrauterine hemolysis and the extent of hemolysis. If the hemolysis is severe, intrauterine blood transfusion may be required and early termination of pregnancy may be necessary. The dilemma in the management of Rh-negative pregnant women in China The most critical drug to prevent sensitization of Rh-negative pregnant women is Rh immunoglobulin (RhoGAM), and since the Rh-negative population in China is relatively small and the amount used is relatively low, foreign pharmaceutical companies are not willing to spend so much time and effort to get it registered by the Chinese pharmacovigilance in order to enter the Chinese market. The current solution to this problem is for patients to purchase the drug themselves from Hong Kong, or to go to a foreign-owned clinic within China for injection. Until this dilemma is resolved, there are some compromises to help minimize the amount of Rh immunoglobulin we need. One is to determine the fetus’ Rh blood type in advance by means of a non-invasive fetal DNA test in the mother’s peripheral blood before 28 weeks, and if the fetus is Rh negative, there is no need for Rh immunoglobulin injections. If the Rh blood type of the fetus cannot be determined in advance, the Rh blood type of the newborn can be determined as soon as possible after birth. Because in principle, Rh immunoglobulin can be injected within 72 hours after delivery, if you know early that the newborn’s Rh blood type is negative, you can have one less injection.