Rh incompatibility during pregnancy: what is it?

Rhesus, what is it?

Do you know your blood group and your rhesus? Whether you have the answer or not, these two pieces of information will be automatically searched from the start of your pregnancy. And it’s not just to have all the information you need on the day of delivery. This information is also required for the welfare of the child to be born during gestation.

But above all, what is rhesus? “All the red blood cells in our cells are with antigenssubstances capable of trigger an immune reactionsimply explains Dr. Dupuis, professor of gynecology and obstetrics in Lyon and author of Childbirth safety at the editions of Chem. “Rhesus, one of those antigens that we call antigen “D”. When the “D” antigen is present in the red blood cells, we are in the presence of a so-called positive rhesus, if the antigen is absent, it is therefore a negative rhesus “he continues.

What are incompatible rhesus? And what are the risks?

An incompatibility occurs when the rhesus of the mother and the child are not the same, but only if the mother is rhesus negative. “If the mother is rhesus negative but the spouse, (the biological father) is rhesus positive, and has this D antigen, then the baby who is developing has a 50 to 100% chance of being rhesus positive. it is in this precise case that one speaks of incompatibility.” says the doctor.

Which blood groups are dangerous for the baby?

As mentioned, it’s not the blood groups which pose a problem and are incompatible, but rhesus, that is to say the presence or absence of the “D” antigen on the red blood cells.

The risk of the mother’s immune system defending itself against her baby

What are the consequences of this incompatibility? They can be serious if no prevention is implemented as explained by the obstetrician. “The risk is that red blood cells from the fetus pass into the maternal bloodstream. And since the mother does not have this D antigen, her organism produce antibodies in response, harmful for the baby.”

A low foeto-maternal risk during a first pregnancy

In theory, this incompatibility does not affect the first pregnancy, because it’s the immune memory that’s dangerous. During the first pregnancy, the mother will produce antibodies called “irregular agglutinins”, or anti-rhesus, to protect herself against them. But the process being initiated, it can be reactivated in the next pregnancy. “In reality, it is even a little more complex, because the very first pregnancy mentioned may be a miscarriage, or even go unnoticed by the woman, when a very early miscarriagemoderates the specialist. Vigilance is therefore essential.

A proven risk from the second pregnancy

In the event of rhesus incompatibility, if the first pregnancy often goes smoothly, things can quickly get complicated from the second (of course, if it is still a rhesus positive dad). “If this new fetus is indeed rhesus positive, when her red blood cells pass into the mother’s blood, the mother’s immune system will recognize them as a threat and produce antibodies “anti D” directed at the red blood cells of the fetus.” explains the doctor. How? Once past the placental barrier, these antibodies will stick to the blood cells of the fetus to destroy them. “The fetus undergoes severe anemia and acute, which can be fatal if nothing is done” he continues. This is why prevention is essential.

Is rhesus screening of the fetus possible? At what moment ?

Today, fortunately, technologies make it possible to determine the rhesus of the fetus by a simple blood test.“We do this test to the mother of rhesus negative at the beginning of the second trimester“, specifies the obstetrician. If the result shows that the baby is rhesus negative, there is no prevention to put in place. If the baby’s rhesus is positive, prevention by an injection of Rhophylac will be scheduled at the 27th week of pregnancy. An injection will also be planned with each pregnancyunless it is a new Rh-negative spouse.

Another mom-side test

There is also a test to determine whether there are red blood cells in the mother’s blood. The kleihauer test, by blood smear, makes it possible to detect red blood cells from the fetus and to quantify them in the blood circulation of the future mother.

Rhophylac injection, what is it for?

In case of incompatible rhesus between the mother and the child, for prevention, an injection of Rophylac (source 1), i.e. anti-D gamma globulin is recommended at the 27th week to avoid complications. Thanks to this injection, the pregnant woman’s immune system will not have no time needed to make your own antibodies. Another will be administered within 72 hours following childbirth. But also in other circumstances that have made possible the passage of red blood cells from the fetus into the maternal blood: after an abortion, an amniocentesis, an ectopic pregnancy, a miscarriage… or a trauma (accident, haemorrhage) occurring during pregnancy. pregnancy.

Here again, technology is fortunately prowess. An American, Dr Giancarlo Mari, discovered in 2000 (source 2) that doppler ultrasound was a way of knowing if there was anemia in the fetus, by simply observing red blood cell velocity. “To put it simply, the red blood cells in the blood vessels are like cars on a highway. If the cars are going very fast, there aren’t many of them. Just like the red blood cells, if they go quickly, it’s because there are too few of them.” illustrates the doctor. “We will measure this speed by Doppler echography, in the middle cerebral artery of the fetus. Depending on the term of the pregnancy, a website makes it possible to know the speeds of the expected red blood cells. “It is a non-invasive method, which uses Doppler ultrasound, without the need to puncture the cord as it could be before.”

What treatment is offered in case of anemia in my baby?

If prevention has not been possible and a Rh incompatibility between mother and child causes severe anemia in the fetus, the solutions depend on the term.

  • If the term is too far to consider giving birth to the childthe fetus is monitored by measuring the regular antibodies and by estimating the degree of anemia of the fetus. In some cases, in utero transfusion in fetal medicine and hospitalization of the mother may be considered.
  • If the term is close enough, labor will be triggered to support this baby from birth.

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