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A: First, important bottom line information for you: while your doctor will watch your baby closely during pregnancy and after birth, severe complications from "little e," as it is called, are unlikely. Different blood antibodies pose different levels of risk, and e is one of the better ones to have.

Next, immunology 101. Our bodies recognize our own proteins as "self" and don't make antibodies against our own cells. Since the fetus has some characteristics from its father, it may express proteins (antigens) that the mother's body sees as "foreign." If the mother's red blood cells don't have a specific protein and the fetus's red cells do, the mother may make antibodies that mark fetal cells for destruction. Complications of blood group sensitization can range from mild to very severe. If a small number of fetal red blood cells are destroyed, the baby may develop jaundice at birth. If a lot of cells are destroyed, a fetus can become anemic, leading (if untreated) to congestive heart failure (fetal hydrops) and even stillbirth. Little e antibodies tend to only have mild effects. Most pregnancies lead to healthy full-term babies.

The most well-known example of maternal antibodies that affect the fetus is Rh sensitization. When moms are sensitized to Rh (also called D), maternal-fetal medicine high-risk specialists watch the baby and provide treatment to prevent serious complications. Treatment may involve delivering the baby early so that medical care can be given in the newborn unit, or actually transfusing blood into the fetus before birth. Rh immunoglobulin (RhoGAM®) is a medication developed in the 1960s to prevent Rh sensitization. Because Rh immunoglobulin works so well, we are seeing fewer cases of Rh sensitization, and proportionally more cases of other types of antibodies, like little e. Again, the bottom line for you: sensitization to e antigen doesn't usually cause the severe problems associated with Rh sensitization.

Your red blood cells must be little e negative or you wouldn't be able to make anti-e antibodies. You may have been exposed to e antigens in a prior pregnancy or during a blood transfusion. Rh immunoglobulin prevents Rh sensitization to "big D," the major Rh protein, but it doesn't prevent sensitization to the e antigen. Once you have antibodies, you will always have them, and every pregnancy will be treated the same. If your baby's father is e positive, he may have passed that characteristic to your baby. If he doesn't have the e antigen, your baby won't have it either (since you don't have it or you wouldn't have been able to make the antibody) and won't be affected at all by the e antibodies. Testing dad is often the first step. If your baby may have e antigen, your doctor will watch closely, by checking your antibody titers (with blood tests), and following ultrasounds. Again remember that the effects of little e tend to be mild, and most pregnancies are delivered at full term without problems. Talk to your doctor for more information and so you can work out the plan of care to keep your baby healthy during pregnancy and beyond.