Fetal anaemia

Pathology description

Fetal anaemia is a decrease in the number of red blood cells (or haematids) in fetal blood to below normal levels.  

The most common cause of fetal anaemia is an incompatibility between the blood type of the pregnant woman and that of the fetus called isoimmunization. In addition, it can also occur as a result of some viral infections that interfere with the fetal bone marrow causing it to produce fewer red blood cells, or in monochorionic twin pregnancies (twin to twin transfusion syndrome, anaemia-polycythaemia sequence). 

What is isoimmunization or erythroblastosis fetalis?

Isoimmunization is a condition caused when a pregnant woman develops antibodies (defences of the human body) against the red blood cells of her fetus. This occurs because the pregnant woman and the fetus have mutually incompatible blood groups. The antibodies created by the pregnant woman cross the placenta, reach the fetal bloodstream and destroy the red blood cells of the fetus, producing anaemia.

It should be noted that for the pregnant woman to produce antibodies against the red blood cells of her fetus, there must have been a previous exposure to these blood cells, for example, through a blood transfusion to the woman or during a previous delivery, at which time the antibodies would have been created. 

The most frequent cause of isoimmunization worldwide is that caused by incompatibility in the Rh factor: the pregnant woman is Rh negative and the fetus is Rh positive. Normally in a first pregnancy there is at some point a contact between the blood of the pregnant woman and the fetus, leaving the pregnant woman sensitized. Therefore, in the second and in any subsequent pregnancies the problem will appear.

To prevent this, a kind of "vaccine", called Gamma globulin anti-D, is given to all Rh-negative pregnant women, which prevents most cases of isoimmunization. However, sometimes isoimmunization can occur in the pregnant woman despite having administered the "vaccine".

What are the consequences of fetal anaemia?

The main function of red blood cells is to transport oxygen through the blood to all organs of the body. Anaemia can be mild and have no consequences or manifest itself only in the newborn, but sometimes it can occur in a severe form already during fetal life.

If left untreated, the fetal heart has to overexert itself to maintain the normal oxygenation of the organs and this can lead to a serious situation of heart failure with fluid accumulation in the body known as hydrops fetalis, which without treatment has a very high risk of fetal death or severe neurodevelopmental sequelae due to the lack of oxygen in the brain. 

Diagnosis

Once it is suspected that the fetus may have anaemia, for example, because the pregnant woman is Rh negative and may have irregular antibodies that attack the fetus' red blood cells, special monitoring needs to be performed.  

In such risk cases, the presence of anaemia can be very reliably suspected based on Doppler ultrasound, by determining the speed of blood in one of the arteries of the fetal brain, the middle cerebral artery.

The definitive diagnosis is made by a fetal blood test. A puncture is made in the umbilical vein, usually in the umbilical cord, which is called cordocentesis, with a fine needle similar that used in amniocentesis, to extract a minimal amount of fetal blood. 

Treatment

Fetal anaemia is treated with an intrauterine transfusion. Until about 30 years ago, most fetuses that had severe anaemia complicated by hydrops fetalis died in the pregnant woman's uterus, but transfusions in utero have allowed more than 90% of these fetuses to survive. 

Intrauterine transfusion is performed with ultrasound control. The procedure is the same as for diagnosis, that is, a puncture in the umbilical vein either in the umbilical cord (cordocentesis) or in its path within the fetal abdomen. Most cases need a minimum of 2-3 transfusions throughout pregnancy, with a consecutive increase in the risk of complications that can become significant.

Possible complications include rupture of membranes and premature birth, but also bleeding due to the puncture with severe haemorrhage and death of the fetus. It requires a lot of experience, but in expert hands it is a technique with very good results. 

What appointments are necessary for fetal surgery?

An in-patient admission of the pregnant woman will initially last 1 day and afterwards weekly check-ups with examination and ultrasound will be required, and she will have to maintain a low-activity lifestyle until the end of pregnancy. Ultrasound control will allow the monitoring of the correct development of the fetus and rule out the presence of signs of the impending development of hydrops fetalis.

Transfusions will normally be needed every 3-4 weeks, depending on the degree of anaemia and the amount of blood administered in each transfusion. The aim is to ensure that childbirth can take place at full term rather than prematurely. 

After birth our paediatric Neonatology Department teams will follow the baby for the first month of life, at which point the mother's antibodies usually disappear from his or her blood and the baby can be definitively discharged. Most treated cases of fetal anaemia will have an excellent long-term prognosis.