RH Factor and Pregnancy and Why it Matters

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Does your “Rh” make any difference in your daily life? Not in the slightest.

But when you’re pregnant, your Rh status can matter, under some circumstances. That’s because your immune system, which monitors your body and bloodstream for foreign cells, recognizes invaders based on the proteins they carry on their surfaces. When cells are littered with proteins that are unfamiliar to the immune system, it will eye those cells more carefully, and, perhaps, attack and destroy them. To your Rh-negative immune system, then, Rh-positive cells look suspicious — even if they belong to your fetus. (An Rh-negative mother can have an Rh-positive fetus if the baby’s father is Rh-positive.) The situation is called Rh incompatibility.

Actually, the term “Rh” refers to a particular protein, the Rh factor, that sits on the surface of red blood cells (the surfaces of all cells are dotted with some protein or another). About 85 percent of the population carries the Rh-factor protein on their cells. That makes them Rh-positive. Some folks, such as you, don’t have the protein and are Rh-negative.

How and when does this incompatibility issue create problems? During the pregnancy, the maternal and fetal blood systems are totally separate. Your blood and your baby’s blood don’t mix, so your immune system has nothing to react to. But during labor and delivery, things get messier (in more ways than one): Drops of the baby’s blood — with those Rh-positive cells — can get in your body, and your immune system will begin to mount an attack.

It makes no difference to the baby just born (it won’t, for example, have any impact on breastfeeding). But now that your immune system is ratcheted up and ready to assail Rh-positive cells, it will do so all the time — most importantly, during any future pregnancy with another Rh-positive baby, leading to anemia or jaundice in the baby. Or worse.

It sounds dire, but the situation can be avoided. That’s where Rhogam comes in. The vaccine-like compound, also known as Rh immunoglobulin, is a blood product that can stop your immune system from attacking Rh-positive cells. When an Rh incompatibility is identified, Rhogam will be given, as a shot, during week 28 of pregnancy (it will also be given after chorionic villus sampling, amniocentesis, miscarriage, ectopic pregnancy, abortion, uterine bleeding, or any trauma during pregnancy that could leak some of the fetal cells over to you) and then again within 72 hours after delivery (if, that is, the baby is indeed Rh-positive; if he or she’s Rh-negative, the shot isn’t necessary because there are no “foreign” cells for your immune system to respond to), ensuring that subsequent pregnancies are as safe as the first.

If you have concerns about getting Rhogam because it is a blood product, keep in mind that there’s no evidence that a disease like AIDS or hepatitis has ever been transmitted through the shot. Meanwhile, its benefits are enormous.