The complications arising from Rhesus incompatibility are enormous. Experts estimates that over 50% of untreated complication due to Rhesus incompatibility result in neonatal deaths. However, not many potential parents are aware of this condition and the few who knew this, find it very complex to understand, partly due to the inherent complexity of the disease process of Rhesus incompatibility. This article will aim to make it as brief and simple as possible. So, you are lucky to have stumbled upon this.
Rhesus incompatibility results from unfavorable pairing of maternal and fetal Rhesus types. Rhesus is also a blood group type that is designated as negative or positive. An individual is either classified as been Rhesus positive or negative based on the presence or absence of an RhD Antigen on their red blood cells. People who have RhD antigen on their red blood cells are simply referred to as Rhesus positive and the absence of it is Rhesus Negative. There are no many Rh-Negative people in the world. ‘Researchers estimate that the frequency of the Rh-negativity occurs more frequently among those of Caucasian (North American and European) descent (15% to 17%) compared to those of African (4% to 8%) or Asian descent (0.1% to 0.3%)’ (Costumbrado J et al. 2021)
An incompatibility results when a Rhesus Negative mother conceives a Rhesus Positive baby. This occurs when the father of the baby is Rhesus Positive. The father has 50% chances of passing on their Rhesus antigens to the fetus. That means a baby whose father is Rhesus positive, is 50% more likely to be Rhesus positive.
When this unfavorable pairing happens, usually during the first pregnancy, the mother becomes sensitized to the Rhesus antigen in the baby’s blood and forms antibodies called Anti D antibodies which are capable of identifying and attacking the Rhesus Antigens on the Red Cells. The D antibodies perceive the Rhesus antigens as foreign bodies the same way, the immune system identify bacteria, viruses and other infecting organisms. This causes a breakdown of the fetal red cells resulting in complications such as jaundice, severe anemia, neonatal heart failure and death. Some survivors also develop neurological and developmental problems.
For sensitization of the maternal antibodies to occur, the fetal blood must enter the maternal blood through one of several ways. The most common means is during child birth (both vaginal and cesarean deliveries). This explains why, children borne to Rhesus incompatible pregnancies turn to not suffer the complications, however, sensitization is initiated and the red cells of subsequent pregnancies become the target of the Anti D antibodies. Once the maternal blood is sensitized, it persists for life and the severity of Rh incompatibility increases with each subsequent Rh-positive pregnancy. Other ways by which maternal antibodies becomes sensitized to Rhesus antigens include miscarriage, abortion, threatened abortion, intra-uterine bleeding due to trauma, invasive medical procedures involving the uterine wall and blood transfusion. However, the risk due to blood transfusion is very minimal due to blood transfusion screening.
During pregnancy, blood testing to determine maternal blood group and rhesus (RhD) status is conducted. RhD negative mothers are further tested for the anti-D antibodies that destroy RhD positive red blood cells. Unfortunately, when anti-D antibodies are detected in maternal blood during pregnancy, the risk for Rh incompatibility has already been established and the only option is a more frequent monitoring of the mother and the fetus during the course of the pregnancy. The baby will usually need to be delivered and monitored in a high monitoring unity.
Alternatively, knowing the paternal Rhesus status can be very helpful in deciding the course of management. If both parents are Rhesus Negative, then there is no risk of Rhesus incompatibility. However, if the father is Rhesus positive (or his Rhesus status is unknown) and the mother is negative, early screening can help with administration of anti-D immunoglobulin which neutralizes any RhD positive antigens that may have entered the maternal blood during pregnancy, thereby preventing sensitization and the subsequent production of the anti-D antibodies.
It is recommended that; all Rh-negative mothers should receive anti-D immunoglobulin during pregnancy as part of a routine antenatal Anti-D prophylaxis, irrespective of whether they have had it during their previous pregnancies. How you received this will be determined by your obstetrician or midwife.
