85. Isoimmunization – Dr. Michelle Tsai, MD

Congratulations on your pregnancy! Whether this is your first or fifth pregnancy, you may never cease to be surprised by how much blood work and testing there is – did they really need that sixth vial of blood? And what are they looking for? One of the first lab tests your doctor may order for you is a blood type and Rh type test.

You may have heard of the different blood types, but have you ever heard of an “Rh negative” blood type? Many patients find out for the first time during pregnancy what their blood type is, including if they have an Rh negative blood type. What is the Rh factor and why is this important in pregnancy?

The Rh factor is a protein that is found on the surface of red blood cells. If you have an Rh negative blood type (like O negative), it means you do not have this protein on the surface of your red blood cells. This is important as we often do not know the blood type of your baby until after birth. An exception to this would be if your partner also has an Rh negative blood type (it does not matter if it is the same ABO blood type as yours,) which would mean your baby is also Rh negative. If you are Rh negative and your partner does not know his blood type or has a Rh positive blood type, you are at risk of isoimmunization.

Any time there is bleeding during pregnancy, the baby’s red blood cells can cross into mom’s circulation. Most often this happens at the time of delivery. If mom is Rh negative and baby is Rh positive, mom’s immune system will recognize the baby’s blood cells as a foreign body and create antibodies to attack these cells. As a result, in the future, if there are again “foreign” cells detected in mom’s circulation, the immune system will attack these cells. This can affect your future pregnancies.

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Let’s look at an example. Mom is Rh negative and had an episode of first trimester bleeding. Her system has been sensitized to the baby’s Rh positive blood cells, and antibodies that have been made against the baby’s blood cells can cross the placenta to attack fetal blood cells. This can cause serious anemia in the baby and endanger the baby’s life. Rh incompatibility can also cause jaundice in a newborn.

Isoimmunization can happen with any bleeding during pregnancy, including miscarriage, ectopic pregnancy, termination of pregnancy, and even with a motor vehicle accident or procedures during pregnancy such as amniocentesis/chorionic villi sampling or external cephalic version.

Luckily, these complications can be prevented. The goal of treatment is to stop mom’s body from making Rh antibodies in the first place. To prevent complications in your pregnancy, if you have an Rh negative blood type, your doctor will offer you an injection called Rhogam (Rh immunoglobulin), which prevents your body from developing Rh antibodies. Rhogam is generally given around 28 weeks of pregnancy and again after delivery, if your baby is Rh positive (baby’s blood type is easily detected after birth!). Each pregnancy and delivery of an Rh-positive baby requires a repeat dose of Rhogam. If you have any invasive procedures done during your pregnancy (like an amniocentesis), your doctor will likely offer you a Rhogam injection at that time as well.

Problems do not usually occur during an Rh-negative mom’s first pregnancy with an Rh-positive baby, as it takes time to develop antibodies against the Rh-positive blood cells. The development of antibodies puts a future pregnancy at risk. If you have any questions in regards to your blood type and if you need Rhogam, please discuss with your OB-GYN. Congratulations again on your upcoming addition to your family!

Check out Dr. Michelle Tsai’s other post here!

Dr. Michelle Tsai grew up in LA’s San Gabriel Valley and received her bachelor’s degree at the University of California – Berkeley. She taught English in Asia for a year prior to attending medical school at Virginia Commonwealth University. She completed her residency training at the University of Hawaii in Honolulu and moved to the San Francisco Bay Area to open her own private practice.

Dr. Tsai is currently an assistant professor of OB-GYN at UCLA. She is the director of the UCLA Marina Del Rey OB/GYN office which is opening in 2023. She divides her time seeing patients in the office, performing gynecologic surgeries, delivering babies, teaching medical students and residents, and serving as an independent contractor in the community for the underserved. When she is not working, she enjoys spending time with her husband and miniature schnauzer Sadie, as well as traveling, exercising, and trying out new restaurants in her community. They welcomed their first child in October 2020.