Isoimmunization and Rh incompatibility

According to the blood type, each person has a series of specific proteins of that sort on the surface of red blood cells, i.e. blood cells.

There exist four blood types: A, B, AB, and 0 (zero). Simultaneously, each one of these four types is classified according to the presence of another protein on the surface of red blood cells. Such protein will determine the Rhesus factor of blood, which may turn out to be either positive or negative. Thus, a total amount of 8 possible combinations may occur, and the four groups can be positive and negative.

Rhesus factor is an antigen or protein that can be found in human red blood cells. In case such antigen is detected, the person is said to be Rh positive, which occurs in 85% of cases. Conversely, if the person lacks this antigen, it is called Rh negative, a rather infrequent possibility as only 15% of total population is Rh negative.

As with blood type, Rh factor is made up of a pair of genes, one of them inherited from the mother and the other one from the father. This is known as dominant inheritance, i.e. if one of the parents is Rh positive, the child will be positive as well. For a person to be negative, both copies of genetic material (the father’s and the mother’s) have to be Rh negative.

How it can affect your pregnancy

With regard to what has been explained above, an important risk can show up during pregnancy, known as isoimmunization or Rh incompatibility. This happens when the mother is Rh negative while the fetus is Rh positive. The fetus and the mother have to coexist in touch with each other’s blood throughout the nine months of pregnancy, something that may lead to blood group incompatibility between the mother and the unborn baby.

It is likely that the mother’s blood starts producing a series of immune defenses or antibodies against the Rh positive blood type of the baby. Nonetheless, this phenomenon is uncommon among first-time moms, since the amount of antibodies generated by the mother against the Rh factor is still low.

However, from second pregnancy onwards, or if she is already immunized due to a previous miscarriage, the maternal bond may be compromised and even lead to fetal death due to the destruction of the baby’s blood cells. This occurs during a woman’s first childbirth: when fetal cells enter the maternal bloodstream, her organism may identify them as strangers and therefore begin producing antibodies to “attack” fetal red blood cells.

Vaccines after pregnancy

Today, the majority of Rh negative women take a blood test when they are around 8-9 weeks pregnant. This test is known as indirect Coombs test (a.k.a. indirect antiglobulin test or IAT), which will be repeated on a monthly basis from month 5 of pregnancy onwards.

Should the IAT be negative, women are advised to administer a dose of anti-D gamma-globulin in order to prevent the appearance of such incompatibility between the woman and the baby. It is also administered when the woman is 28 weeks pregnant in cases where she is Rh positive and her partner is Rh negative.

Globulin prematurely destroys fetal red blood cells that may enter maternal blood, avoiding therefore the production of antibodies against the baby’s Rh+ red blood cells. Since this allows the accumulation of antibodies in maternal blood to be avoided, following pregnancies will develop as the first one thanks to the prevention of an excessive Rh sensitization.

In case the levels anti-Rh antibodies become too high, a thorough follow-up should be scheduled. In most complicated cases in which the vaccine does not work, intrauterine fetal blood transfusions through the umbilical cord under ultrasound control will be performed. After childbirth, babies affected by this incompatibility have to be thoroughly monitored in order to rule out or immeditely treat symptoms of anemia and jaundice, if any.

2 comments

  1. usuario
    Mercedes Kennedy

    Hi! I did an IVF with donor sperm and now I’m pregnant with twins! I’m 0- and he’s also 0-. Does it mean my babies will also be 0-???

    • avatar
      Sandra F.Fertility counselor

      Hello Mercedes,

      Yes, you are right. Your babies will be 0- as well.

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