Rhesus factor determination in pregnancy

NEW - determination of the child's rhesus factor with cost covered by the insurance companies

During the first blood test in pregnancy, the blood group (A, B, 0) including the rhesus factor D is determined.

What is a rhesus factor?

The rhesus factor D is a protein on the surface of the red blood cells. Most people (85% in Europe) have this factor. They are rhesus positive. Pregnant women with a positive rhesus factor do not pose any health risks to the child.

Possible complications in a rhesus factor-negative mother

In a Rhesus-negative mother expecting a Rhesus-positive child (inherited through the father), there is a risk that the mother's immune system will produce antibodies when the mother's blood comes into contact with the child's blood. This often happens during birth, more rarely during pregnancy. If this woman becomes pregnant again after the formation of antibodies, the anti-D antibody concentration increases significantly. This in turn leads to severe anaemia in the unborn child.

Previous approach to mother & child safety

Up to now, all women who are Rh negative have been injected with Rh prophylaxis in the 28th-30th week of pregnancy. This was done across the board, because it was not possible to determine during pregnancy whether the child was Rh positive or negative.  This prevented the formation of anti-D. Children of RhD-negative women are RhD-positive in about 60% of cases, and RhD-negative in about 40%. Thus, 40% of the injections were given although they were not necessary.

The preparations for Rh prophylaxis are human anti-D immunoglobulins, using blood donations from humans. Even though the preparations are well tested and very safe, they are still blood products.

Latest developments

A new development is to take blood from the pregnant woman (from the 11+0 week of pregnancy) and determine the fetal rhesus factor from the fetal cells (free fetal DNA, genetic material of the unborn child) found in the maternal blood. Rhesus prophylaxis is then only administered to pregnant women in the 28th-30th week of pregnancy if the child has tested RhD-positive.

Studies have shown that the old method (Rh prophylaxis for all Rh-negative pregnant women) is just as effective as the new one (targeted Rh prophylaxis after fetal blood grouping).

However, one should be aware that in very rare cases there are misdiagnoses. This is very rare and the cause is usually due to an insufficient amount of fetal material. Therefore, although it is possible to determine the Rhesus factor from 11+0 weeks of gestation, it is advisable to wait until after the 20th week of gestation if possible. Because then there are enough fetal cells in the mother's blood. To be on the safe side, the Rhesus factor is always determined again after delivery from the umbilical cord in order to find out the few cases in which an administration was missed (which is very unlikely: less than 0.5Promille).

The pregnant woman herself is free to decide which of the two methods she chooses. Both are covered by the health insurance (since 01.07.2021).

Please be sure to seek advice from the attending physician. This blog is for informational purposes only.

July 2021 - Gravidamiga 
This blog post has been prepared with the greatest possible care and does not claim to be correct, complete or up-to-date.“ This is not a medical post and it does NOT substitute a visit to a doctor.

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