Edited by Eugenio Ciuccetti, Obstetrician
See also: Coombs test
What does it mean?
By maternal-fetal incompatibility we mean a condition characterized by the presence in the unborn child of a different blood group, and indeed incompatible, with respect to that of the mother. Blood group that, in this case, the fetus will obviously have inherited from the father. More specifically, therefore, the fetal erythrocyte antigens will not be recognized by the woman's immune system, which will therefore tend to immunize against them.
We talk about Neonatal Hemolytic Disease (MEN) to indicate the condition in which fetal red blood cells are destroyed by maternal antibodies; hence consequences such as haemolytic anemia, jaundice, hepatosplenomegaly, brain damage.
Risks after the first pregnancy
The problem of maternal-fetal incompatibility is not so much the first pregnancy characterized by the contact between different blood groups, but rather the subsequent ones in which this incompatibility should recur.
In fact, the first pregnancy will be one in which the possible contact between maternal and fetal blood will lead the mother to "becoming aware". Later pregnancies, however, may be those in which this immunization will produce its real negative effects on the fetus. In order for this to happen, however, some other fundamental circumstances must also occur: for example, maternal antibodies will have to pass the placenta in sufficient quantity to be able to effectively target the fetal antigens.
It should be noted, in this regard, that if the same passage of fetal blood in the maternal circulation - especially during childbirth and secondary birth - is quite frequent, on the other hand it is not, at least in most cases, quantitatively sufficient to stimulate the maternal immune reaction.
Risk blood groups
In this context it should also be noted that the existing blood groups - characterized by different antigens - are in fact numerous; however the problem of maternal-fetal incompatibility mainly concerns the AB0 and Rh systems.
The first case is more frequent but generally less severe. The second one instead implies the greatest risks and occurs when a negative Rh mother conceives a Rh child as positive as the father. There are no problems - at least from this specific point of view - if both parents are Rh positive, if both are Rh negative or if the mother is Rh positive and the fetus Rh negative.
Indirect Coombs test
For this reason, today, it is essential to know promptly the blood group and the Rh factor of every pregnant woman and perform the so-called indirect Coombs Test on Rh negative pregnant women. For preventive purposes, then, anti-D immunoglobulins will be rapidly administered to all Rh negative women who will have given birth to a Rh positive child. This is precisely to counteract the risk of sensitization and consequent immunization. In the prevalence of cases, in fact, it is precisely the presence or absence of the antigen D that characterizes the belonging to the Rh positive or Rh negative group respectively. To verify this, however, every time the Coombs Test is positive, the so-called "typing" and "titration" of the antibodies will also be performed. This will precisely clarify the type of antibody and the degree of positivity we will be dealing with.
