What is Rh incompatibility

The presence of a negative Rh factor (Rh(-) factor) in the mother and a positive Rh factor (Rh(+) factor) in the father is called Rh incompatibility.

The Rh factor consists of small protein bodies, antigens, on erythrocytes, our red blood cells. Most people have them, and this is called Rh (+) factor; if a person does not have them, this is called Rh (-). There are 3 types of antigens (CDE), but the antigen that causes the greatest problems is antigen D.

The blood group itself may be any group (that is, the pregnant woman and her spouse may have any combination of blood groups I, II, III, IV); only the Rh combination described above is considered Rh incompatibility.

The opposite combination, that is, the mother having Rh(+) and the father Rh(-), or matching Rh factors, are not Rh incompatibility.

The child may inherit either a negative Rh or a positive Rh. If it is Rh(-), then there will be no problem. However, with a positive Rh factor, Rh conflict may develop in some cases. I would like to immediately reassure parents who have Rh incompatibility: nowadays, thanks to injections, early diagnosis, and monitoring, Rh conflict develops extremely rarely.

Rh incompatibility is observed on average in 13% of couples, but only 1% develop Rh conflict. Thus, Rh incompatibility and Rh conflict are not the same thing, and not every couple with Rh incompatibility develops Rh conflict. I am writing about this in such detail because there is great confusion about it. Unfortunately, not only among patients, but also among doctors. We often see couples who, with tragedy in their voices, tell us that they are Rh incompatible and that they will most likely have a miscarriage or a stillborn child!!!

What happens in Rh incompatibility?

In the presence of Rh incompatibility, if the child has a positive Rh, red blood cells (erythrocytes) of the fetus may enter the mother’s bloodstream during pregnancy or childbirth. Only then, when the mother’s and the fetus’s blood mix, does the defense mechanism start. The fetal erythrocytes carry Rh positive antigens (including the strongest D antigen). The mother will defend herself against them, because her own body does not have them, by producing antibodies, her own army, of two types: M and G, in order to destroy the foreign bodies. Normally, the blood of the baby and the mother do not come into contact: the mother has her own circulatory system, and the fetus has its own. Only useful substances that serve the nutrition and growth of the fetus pass from the mother to the child. Moreover, before reaching the child, they must pass through the placental barrier, a strict inspector blocking suspicious and obviously harmful substances. M antibodies do not pass through this barrier, so they do not harm the child. G antibodies are produced slowly, over 3 to 6 weeks, and are not dangerous in late pregnancy either. Since there were no antibodies before pregnancy, in the first pregnancy conflict usually does not occur, because for the first time the mother’s body produces them in very small quantities.

The problem is that our defense mechanism is a very clever thing: just as in the fight against infection, the immune system retains a memory of the enemy. In subsequent pregnancies, again only if the child inherits a positive Rh, the production of antibodies in an organism prepared for the encounter occurs much faster and in much greater quantity. Then G antibodies may enter the fetus’s blood with the aim of destroying the antigens, but at the same time the fetal erythrocytes are destroyed, which leads to the development of intrauterine hemolytic anemia of varying severity.

In mild anemia, no changes are visible on fetal ultrasound; in moderate anemia, a condition called erythroblastosis is observed, meaning the replacement of destroyed erythrocytes by a young team of cells as a defense against anemia. In this case, the pigment bilirubin is released from the destroyed erythrocytes, a substance that is deposited in the body’s tissues, staining them yellow, jaundice, and also being very dangerous for the fetal brain. In addition, due to developing heart failure, the fetus retains fluid in the body: between the layers of the abdominal cavity, around the lungs, heart, and so on.

This condition is called hydrops fetalis and is dangerous for fetal life. Fortunately, severe complications in the fetus develop extremely rarely: only in 10% of all Rh conflict cases. Let me remind you of the statistics: only 13% of couples have Rh incompatibility, only 1% of these couples develop Rh conflict, and only 10% of all Rh conflicts manifest in severe form! Most often these are cases where the pregnant woman did not visit doctors, did not register in time for prenatal care, or refused the Rho-gam injection. Therefore, early consultation with a doctor and regular observation will help you give birth to a healthy baby.

Conditions in which the mother’s and fetus’s blood may come into contact

What should be done?

In the above-listed cases, in order to destroy the antigen in the mother’s body, the mother is immunized: an injection of anti-D gamma globulin (Rhogam 300 mgr) is given within the first 3 days after the above-listed conditions. Anti-D gamma globulin, another name for anti-Rh D immunoglobulin, destroys the D antigen in the body of the pregnant or postpartum woman and prevents the immune reaction from starting. Since the antigens will be neutralized, the mother will not need to produce antibodies, and there will be no danger in subsequent pregnancies. Published data say that it is not too late to immunize within 14 to 28 days, because as stated above, dangerous G antibodies are formed within 3 to 6 weeks, but in practice the injection is usually given within the first 3 days.

How is pregnancy managed in Rh incompatibility and how is Rh conflict diagnosed?

If the pregnant woman has a negative Rh and her spouse has a positive Rh, at the first visit a test to detect antibodies is performed, called the indirect Coombs test. If the result is negative, that is, everything is fine and antibodies have not formed, the test is repeated at 20 weeks and then monitored every 4 weeks. If the result is positive, that is, antibodies are detected, their level in the blood is determined: 1/16 means no risk to the fetus, 1/32 and higher means additional investigation is necessary: a detailed fetal ultrasound in a perinatology department and amniocentesis. Amniocentesis is the collection of a small amount of amniotic fluid by means of a procedure very similar to an ordinary injection, only in the area around the navel of the pregnant woman. This makes it possible to assess the condition of the fetus, the degree of anemia, and to develop treatment tactics: deciding on intrauterine blood transfusion to the child, replacing the destroyed fetal erythrocytes and thereby correcting the anemia, and on early delivery.

Blood group incompatibility

Is incompatibility by blood group possible? As a rule, if the mother has group I, O, and the father has group II, A, or III, B, and accordingly the child has group II, A, or III, B, this is referred to as blood group incompatibility. Occurring in about 20% of cases, even more often than Rh incompatibility, it is not of major importance in practice because if conflict develops, it proceeds in a very mild form. Unlike Rh conflict, it may also develop in the first pregnancy, but it does not become more dangerous in subsequent pregnancies. The reason for the mild course is a weaker protective response, because there are few A and B antigens on the surface of erythrocytes; the mother’s body most often forms M antibodies, which do not pass through the placenta, and produces G antibodies in very small quantities. Because of the mild course, there are no tests for intrauterine detection of blood group conflict, and no amniocentesis or treatment before delivery is required. If after birth the child develops early jaundice, due to destruction of erythrocytes and deposition of bilirubin in tissues, blood group conflict is suspected and a Coombs test is performed. As a rule, phototherapy is sufficient for treatment.

This is interesting

1. Combination of Rh conflict and blood group conflict

With blood group conflict, Rh conflict proceeds much more mildly. The mother’s antibodies against A and B antigens reduce the number of Rh(+) fetal erythrocytes, acting similarly to an anti-D gamma globulin injection.

2. The grandmother theory of Rh inheritance

According to this theory, the fetal Rh antigens are inherited from the child’s grandmother, the mother’s mother. For example: the child is Rh(+), and the mother is Rh(-). That means the grandmother was Rh(+). Or vice versa, a Rh-positive mother has a Rh(-) child. Look at the Rh factor of the mother’s mother: it will be negative!

In brief

Rh incompatibility is the presence of a negative Rh factor, Rh(-), in the mother and a positive Rh factor, Rh(+), in the father.

Rh factor: protein bodies, antigens, on erythrocytes. They either exist, Rh (+), or do not exist, Rh (-).

If the child inherits Rh(-), there will be no problem. With a positive Rh factor, Rh conflict may develop: in only 1% of Rh incompatibility cases.

Rh conflict can be triggered by the following conditions: miscarriage, abortion, missed miscarriage, ectopic pregnancy, bleeding during pregnancy, twin pregnancy, childbirth, amniocentesis, chorionic biopsy, trauma during pregnancy, and low-lying placenta.

In these cases, the mother is immunized: an injection of anti-D gamma globulin is given within the first 3 days. Anti-D gamma globulin destroys the D antigen in the body of the pregnant or postpartum woman and prevents the immune reaction from starting.

Pregnancy management: if the pregnant woman has a negative Rh and her spouse has a positive Rh, at the first visit an antibody detection test is carried out and then monitored every 4 weeks. If the result shows antibodies, their blood level is determined: 1/16 means no risk to the fetus, 1/32 and higher means additional investigation is necessary: detailed fetal ultrasound in a perinatology department and amniocentesis. During this, the condition of the fetus is evaluated and treatment tactics are developed.

Treatment tactics

• Observation, sufficient in 90% of cases.
• Intrauterine blood transfusion to the child.
• Early delivery.