Rh Factor of a child

Rhesus (Rh) factor

  • 10-07-2021
Rh Factor of a child

The blood type is determined by molecules on the surface of red blood cells. If the red blood cells have antigen A, then you have blood group A. If antigen B is present, your blood group is type B. In the presence of both A and B antigens, your blood group is type AB. And in the absence of these antigens, you have blood group type O.

Rh factor is a protein that is also found on the surface of red blood cells. If this protein (antigen D) is in the blood, then you have a positive Rh factor (Rh +). If this protein is not in the blood, then the Rh factor is negative. Rh positive is the most common blood type.

Taking into account the blood group according to the ABO system, as well as the Rh factor, the main blood groups can be distinguished:

  • O+, O-
  • A+, A-
  • B+, B-
  • AB+, AB-

Pregnancy and Rhesus (Rh) Factor

The presence or absence of Rh factor in the blood does not affect health in any way. However, some problems can arise during pregnancy if the mother is Rh negative, and the baby is Rh positive.

If the baby's blood enters the mother's bloodstream, Rh antibodies may be produced in the mother's blood. These antibodies can enter the placenta and attack the baby's blood cells.

Usually, the baby's and mother's blood are only mixed during childbirth. Therefore, different Rh factors in mother and child are not a problem during the first pregnancy.

In addition to childbirth, other factors, such as bleeding during pregnancy, amniocentesis, miscarriage, ectopic pregnancy, can also cause the baby's blood to enter the mother's bloodstream.


The Rh factor is inherited from parents. The child inherits a set of genes from the mother, and the same set from the father. As a result, each gene is present in two copies (alleles) passed down from each of the parents.

The allele that contains the D antigen (Rh+) is dominant. An allele that does NOT contain the D antigen (Rh-) is recessive. This means that if one person has two different alleles, then his Rh factor will still be positive, since the allele with the D antigen dominates over the allele in which this antigen is absent.

Conventionally, an allele with an antigen is denoted by a capital D, and an allele without an antigen is denoted by a small d.

For example, both the mother and father have a positive Rh factor. But each of them has different alleles responsible for the Rh factor. One allele contains the D antigen, while the other not. One of the father's alleles and one of the mother's alleles can be transmitted to the child at random.

A simple Punnett square illustrates this example:

 Punnett square. Rhesus (Rh) factor

This means that in 75% of cases, the child will have a positive Rh factor, and in 25% of cases negative Rh factor. That is, even if both parents are Rh-positive, they may have a Rh-negative baby.

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