Blood Incompatibility in Pregnancy

Prenatal care is essential to avoid the risks of a pregnancy with blood incompatibility, especially in relation to the RH factor.

As soon as the mother knows she is pregnant, she makes an appointment to visit the doctor to start prenatal care. In every early pregnancy, numerous tests and tests are required, including blood typing and the Rh factor of the mother and father to find out if there is a risk of incompatibility between the blood of the mother and the fetus.

According to Dr. Antônio Braga, obstetrician at the Santa Casa da Misericórdia Maternity Hospital in Rio de Janeiro, there are actually some types of blood incompatibility. The main one is the incompatibility of the ABO system, when the mother’s blood is different from the father’s blood, regardless of the Rh factor. “In that case, there’s not much to worry about. The most that happens is that the child develops jaundice, which is more yellowish than normal. It can be treated in the maternity hospital with phototherapy.”, explains the specialist. Appropriate treatment will be indicated by the doctor. In 2% of cases of incompatibility due to blood types, they occur in types not normally researched.

The physician’s main concern is the incompatibility of the Rh system, which occurs if the baby has a positive Rh inherited from the father and the mother has a negative Rh factor. As this incompatibility is much less frequent, it presents the most severe cases of hemolytic disease of the newborn or fetal eristoblastosis. In this disease, the fetus can die during pregnancy or after birth. Hemolytic disease can also result in a newborn with profound anemia, causing severe jaundice, as well as deafness and cerebral palsy.

When there is blood incompatibility due to the Rh factor, there is sensitization in the mother, as her blood recognizes the baby as an “intruder” and starts to create antibodies against it. Since the antibodies that are produced in the first pregnancy are large molecules, they are not able to cross the placental barrier. Therefore, in the first pregnancy, if the mother’s blood comes into contact with the baby’s blood that is incompatible, nothing happens. But if you get pregnant again and the mother has not had the proper treatment in the previous pregnancy, the antibodies that are produced are smaller molecules, which are able to cross the placenta and will destroy the baby’s red blood cells. “The destruction of red blood cells causes severe anemia and can cause generalized fetal edema, increased amniotic fluid and even the baby’s death. Babies who survive have severe anemia or rare jaundice”, explains Dr Antônio Braga.

To prevent blood type problems, the mother should start prenatal care as soon as she knows she is expecting her baby. The obstetrician must do a detailed research on the mother’s clinical history to look for situations that may have touched her. Even with this care, Braga explains that prevention must be done with a drug called anti-D, which prevents sensitization, in the first 72 hours postpartum. “In cases of pregnant women who have already been affected, in the second pregnancy they must be accompanied at a Reference Center or by a specialist in High-Risk Pregnancy so that nothing happens to the fetus”, warns the obstetrician.

Recurring Doubts

Can parents with the same Rh have children with hemolytic problems?

There are cases that even if the parents have the same Rh, the child is born with some hemolytic disease. This is due to the incompatibility of the ABO system, which normally does not develop serious diseases, at most a mild jaundice, yellowish skin color that can be corrected with phototherapy treatment in the nursery. According to Dr. Antônio Braga, obstetrician at the Santa Casa da Misericórdia Maternity Hospital in Rio de Janeiro, another reason that can cause blood diseases, in the case of equal Rh between parents, is the incompatibility of irregular antibodies, the most common of which is the Duff. These are rarer, reach 2% of cases and are only researched when there is a serious illness for no apparent reason.

After having a baby born with fetal eristoblastosis, what should the mother do to get pregnant again without risk?

In cases where the mother has Rh (–) and the baby has Rh (+) there are risks of sensitization in the blood, after the first birth the mother must have a vaccine within 72 hours, so that sensitization does not occur in the next pregnancy. Mothers who have already been sensitized, who have had abortions or babies with eristoblastosis need prenatal care in a specialized center, as they are more likely to have another baby with the disease or to lose the baby.

What vaccines do doctors give to pregnant women with Rh (-) protect against?

Vaccines given to pregnant women with Rh(-) who are likely to have children with Rh(+) serve to prevent the mother’s blood from recognizing the baby as a “foreign body” and attacking its cells. The vaccine prevents the mother from sensitizing herself against Rh(+) blood and does not cause any problems for the baby.

Consult your doctor to find out if your case deserves special attention.

For the sake of curiosity, we provide below the blood types and Rh factor tables.

Crossing table between ABO blood types

FatherMotherSons
AAA ou O
ABA, B, AB, ou O
AOA ou O
AABA, B ou AB
BAA, B, O ou AB
BBB ou O
BOB ou O
BABA, B ou AB
OAO ou A
OOO
OBO ou B
OABA ou B
ABAA, B ou AB
ABBA, B ou AB
ABOA ou B
ABABA, B ou AB

Crossing table of Rh factor and genotypes (RR, Rr and rr)

FatherMotherSoons
Rh+ (RR)Rh+ (RR)Rh+ (RR)
Rh+ (RR)Rh+ (Rr)Rh+ (RR ou Rr)
Rh+ (RR)Rh- (rr)Rh+ (Rr)
Rh+ (Rr)Rh+ (RR)Rh+ (RR ou Rr)
Rh+ (Rr)Rh+ (Rr)Rh+ (RR ou Rr) ou Rh- (rr)
Rh+ (Rr)Rh- (rr)Rh+ (Rr) ou Rh- (rr)
Rh- (rr)Rh+ (RR)Rh+ (Rr)
Rh- (rr)Rh+ (Rr)Rh+ (Rr) ou Rh- (rr)
Rh- (rr)Rh- (rr)Rh- (rr)

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