Specifically, Rh can be positive or negative, meaning that Rh-positive people have a unique mark on the surface of each red blood cell that Rh-negative people lack.

Rh-positive people can receive an Rh-negative blood transfusion because the red blood cells are like yours without that little identification card on their surface; so far, no problem. However, it cannot be done the other way around. Suppose we put an Rh-negative individual in contact with those marked red blood cells, expressing an identification they do not have. In that case, they will recognize them as something foreign and generate antibodies destined to destroy each labelled blood cell they find. In our environment, practically 85% of the population is Rh-positive and only 15% negative. The contact can be due to a poorly chosen blood transfusion due to the exchange of syringes… All these situations must be avoided. And also in pregnancy…

And what happens in pregnancy?

When an Rh-negative woman becomes pregnant, if the father is Rh-positive, the fetus can be harmful like the mother or positive like the father; this is called Rh incompatibility. During normal pregnancy, there should be no problem if the mother has never previously been in contact with Rh-positive blood because the blood of the fetus and the mother do not come into contact. Still, there are situations in which this contact can occur: any bleeding during pregnancy, an invasive technique such as amniocentesis or chorionic biopsy, abortion or ectopic pregnancy, or during childbirth. When this happens, the Rh-negative mother initiates this reaction, and the pregnant woman is permanently immunized against Rh-positive blood, called Rh Isoimmunization. In the current pregnancy, there is no time for the reaction to be severe. The problem will be in subsequent pregnancies since, from the early stages of pregnancy, those antibodies present in the maternal blood will be dedicated to destroying the fetal red blood cells causing a picture of fetal anemia and a complex syndrome that can have severe consequences called Neonatal Hemolytic Disease.

Can it be avoided?

Yes! Effortlessly, administering to the pregnant woman a dose of those same antibodies that she could generate, thus tricking her immune system, which trusts itself, as if someone had done its job and thus it is no longer necessary for it to generate its antibodies against labelled red blood cells.

Rh incompatibility in pregnancy: blood analgesics in a pregnant woman

When is it necessary to do it?

This medication, called anti-D gamma globulin, must be administered in each situation that may favour fetal blood contact with maternal blood.

In significant bleeding in the first trimester
Post-abortion or ectopic pregnancy
Post amniocentesis or chorion biopsy.
Also, in a protocolized way, at week 28 of pregnancy.

In all these situations, we do it without knowing the fetal Rh, which, if it is harmful like the mother’s, would not be necessary, but it would not be harmful either. In the postpartum period, we know the Rh of the newborn since a blood sample from the umbilical cord is always taken, and the blood group is analyzed. In this case, gamma globulin is only administered when the baby is Rh-positive.

If this precaution has not been taken, we will detect maternal antibodies, which are requested in the analysis of each trimester of pregnancy from all pregnant women, through a simple blood test called the Coombs Test. In the case of positivity and hemolytic disease, we will study if there is fetal anemia and its degree using Doppler ultrasound. In severe cases, it may be necessary to transfuse the fetus inside the uterus until it is viable and can be removed, which is why it is so vital to administer postpartum gamma globulin when necessary.

This simple measure has been carried out systematically since the 1960s. This pathology has almost completely disappeared in developed countries, which at that time caused the death of 48 out of every 100,000 newborns.

WHAT YOU SHOULD KNOW…

When an Rh-negative woman becomes pregnant, if the father is Rh-positive, the fetus can be harmful like the mother or positive like the father; this is called Rh incompatibility.
In a normal pregnancy, there should be no problem if the mother has never previously been in contact with Rh-positive blood because the blood of the fetus and the mother do not come into contact. Still, there are situations where there can be such contact, and then it's time to act.
In each situation that may favour contact of fetal blood with maternal blood, this medication, called anti-D gamma globulin, must be administered.