Pregnancy and Rh Incompatibility
Although it is often said that opposites attract, this may not be the case when talking about blood types. Blood types, similar to eye color or height, are inherited from your parents through genes. The combination of these genes can give rise to either A, B, AB, or O blood groups, as well as dictate whether the Rhesus (Rh) factor, a red blood cell surface protein, will be present (+) or absent (-). Only two-thirds of Americans know their blood type, information that can be lifesaving, particularly in the case of an emergency, due to the essential role blood plays in sustaining life. Specifically, the Rh factor is known as one of the most complex blood group systems and about 85% of the population is composed of Rh-positive individuals. It gives us insight on whether the blood of two different individuals is incompatible when mixed, like in the instance of a mother and her baby at birth.
Think of a scenario where an Rh-negative pregnant woman carries an Rh-positive baby, this difference in blood type is known as Rh incompatibility. The discordant pairing is due to the baby inheriting the paternal dominant Rh factor gene, which in the case of an Rh-negative mother and an Rh-positive father the likelihood is about 50% or greater. Normally, the baby’s blood does not enter the mother’s circulatory system throughout the course of the pregnancy, rendering this discordancy momentarily innocuous. However, during delivery, the baby’s blood can enter the mother’s bloodstream, causing the mother’s body to recognize the baby’s blood as foreign. This activates the mother’s immune system to trigger the production of antibodies, glycoprotein molecules that can recognize and induce the destruction of the foreign particle. Generally, this does not pose a problem during the first pregnancy, but the permanence of these antibodies against the Rh factor antigen can confer complications for future pregnancies such as Erythroblastosis Fetalis, also known as Rhesus disease.
During a subsequent pregnancy, the Rh antibodies that were previously generated can cross the maternal-fetal barrier and attach to the baby’s Rh-positive blood cells. This primarily occurs during the second or third trimester, which is when the mother’s body releases antibodies to the baby via the placenta as a form of passive immunity with the intention of protecting the baby. However, because the mother has antibodies against the baby’s Rh-positive blood cells it will mistakenly prompt the destruction of the baby’s red blood cells at a rate that exceeds the body’s ability to regenerate them, causing Rhesus disease. The depletion of available red blood cells to the baby can be fatal, due to its vital role in transporting oxygen to different tissues in the body. In very rare cases, the baby will need to undergo intrauterine fetal transfusion, which stabilizes the baby’s level of red blood cells by replacing it with Rh-negative blood cells, in order to minimize the effects of the Rh antibodies produced by the mother. Newborns often present symptoms such as jaundice, anemia, lethargy, and low muscle tone which puts them at risk for brain damage, liver failure, and heart failure.
Nevertheless, advances in pharmaceutical medicine have played a big role in the prevention of Rhesus disease. In the 1960s, a physician at Columbia University Vagelos College of Physicians and Surgeons developed the RhoGAM vaccine, which still today has saved the lives of many newborns. RhoGAM works by blocking the Rh-negative mother’s ability to make Rh factor antibodies; however, this can only be useful if she has not been previously exposed to the Rh factor antigen. It is administered during the seventh month of each pregnancy and 72 hours after delivery to lower the risk for Rhesus disease.
The effectiveness of RhoGAM and its dependability on timing and precaution highlights the importance of prompt and suitable prenatal care and screening by obstetricians. A simple blood test and antibody screening, along with proper treatment and surveillance, can help mitigate or prevent the effects of Rh incompatibility. This reveals how knowing your Rh status can someday save the life of your baby. Ultimately, early detection, treatment, and surveillance can help expecting parents have the peace of mind to focus on welcoming a healthy baby.
References:
ACOG: The American College of Obstetricians and Gynecologists. “The Rh Factor: How It Can Affect Your Pregnancy.” ACOG: The American College of Obstetricians and Gynecologists, ACOG: The American College of Obstetricians and Gynecologists, June 2020, https://www.acog.org/patient-resources/faqs/pregnancy/the-rh-factor-how-it-can-affect-your-pregnancy.
American Red Cross. “Facts About Blood and Blood Types.” American Red Cross, American Red Cross, https://www.redcrossblood.org/donate-blood/blood-types.html.
Fuentes, Armando. “Rh Incompatibility During Pregnancy.” KidsHealth, KidsHealth, October 2018, https://kidshealth.org/en/parents/rh.html.
Neighbor, Joe. “RhoGAM at 50: A Columbia Drug Still Saving Lives of Newborns.” Columbia University Irving Medical Center, Columbia University, 22 February 2018, https://www.cuimc.columbia.edu/news/rhogam-50-columbia-drug-still-saving-lives-newborns.
NIH: National Heart, Lung, and Blood Institute. “Rh Incompatibility.” NIH: National Heart, Lung, and Blood Institute, NIH: National Heart, Lung, and Blood Institute, https://www.nhlbi.nih.gov/health-topics/rh-incompatibility#:~:text=Rh%20incompatibility%20is%20a%20condition,you're%20Rh%2Dpositive.
“Pregnancy and birth: What is the benefit of determining the Rh factor before birth?” IQWiG: Institute for Quality and Efficiency in Health Care, 2019. NCBI, https://www.ncbi.nlm.nih.gov/books/NBK546246/.
