If your blood type is Rh negative, you will probably be given a medication called Rhogam. But why is this necessary, and will being Rh negative cause problems to you or your baby? Obstetrician/Gynecologist David Barrere explains Rh sensitization and how it is prevented.
Can you tell me about Rhogam? I am interested in knowing when and why it is necessary and also how this substance is made. Thank you. – Heather in Boulder, Colorado
The expert answers
Rhogam (Rh Immune Globulin) is an injectable medication used to modulate the mother’s immune system to prevent a condition known as Rh isoimmunization.
Red blood cells can contain a surface protein called the D antigen. The presence of this protein is synonymous with the term Rh positive (e.g. O+, A+, B+, AB+); the absence is synonymous with the term Rh negative (i.g. O-, A-, B-, AB-). In each pregnancy, there is some mixing of maternal and fetal blood, but to varying degrees. If an Rh negative woman is exposed to Rh positive blood, either by exposure to an Rh positive fetus’ blood or by a previous improperly matched transfusion, the woman will produce antibodies in response to the foreign substance. This process is called sensitization, which is the first step in Rh isoimmunization. Rh isoimmunization cannot occur if a mother is Rh positive.
After being “sensitized,” subsequent pregnancies are potentially at risk, but only if the fetus is Rh positive. The antibodies produced (anti-D) can cross the placenta and attack the fetus’s red blood cells, which can cause a life threatening anemic condition (hydrops fetalis). To prevent this, all woman have blood tests early in pregnancy to detect blood type, Rh status, and the presence of any abnormal antibodies, such as anti-D.
All women who are Rh negative, and not already sensitized, receive Rhogam at 28 weeks of gestation. This prevents sensitization by the mixing of maternal blood with fetal blood. After delivery, the blood type of the child is determined. If the child is Rh positive, another dose of Rhogam is required within 72 hours of delivery. If the child is Rh negative, there is no further Rhogam requirement. It is important to remember that this process must be repeated for each subsequent pregnancy.
Rhogam is also given to Rh negative women who have miscarried [or have an abortion] or who are undergoing certain procedures such as chorionic villus sampling (CVS), amniocentesis, or external cephalic version. This is done as there is again the potential for mixing of maternal and fetal blood.
To create Rhogam, serum is obtained from Rh negative individuals who have been exposed to Rh positive red blood cells. Fractionation of the blood plasma is done by a modification of the cold alcohol procedure. Glycine is included in the final product as a stabilizer. Rhogam is given to provide antibody mediated immune suppression (AMIS). The antibody in Rhogam binds to any fetal blood cells that may have entered the maternal circulation. In doing so, it is functionally “removed” from the circulation before the mother can mount her own antibody response, thus preventing sensitization and isoimmunization.