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What is my Rh status and why do I need to know it?
Early in your pregnancy your blood will be tested to determine your blood type and your Rh status — that is, whether you have the Rh (Rhesus) factor, a protein that most people have on the surface of their red blood cells.
If you do have the Rh factor, as most people do, your status is Rh-positive. (About 85 percent of Caucasians are Rh-positive, as are 90 to 95 percent of African Americans and 98 to 99 percent of Asian Americans.) If you don't have it, you're Rh-negative, and you'll need to take certain precautions during your pregnancy.
If you're Rh-negative, there's a good chance that your blood is incompatible with your baby's blood, which is likely to be Rh-positive. You probably won't know this for sure until the baby is born, but in most cases you have to assume it, just to be safe.
Being Rh-incompatible isn't likely to harm you or your baby during this pregnancy, if it's your first. But if your baby's blood leaks into yours (as it can at certain times during pregnancy and at birth), your immune system will start to produce antibodies against this Rh-positive blood. If that happens, you'll become Rh-sensitized — and the next time you're pregnant with an Rh-positive baby, those antibodies may attack your baby's blood.
Fortunately, you can avoid becoming Rh-sensitized by getting an injection of a drug called Rh immune globulin whenever there's a chance that your blood has been exposed to the baby's blood.
If you're Rh-negative and you've been pregnant before but didn't get this shot, another routine prenatal blood test will tell you whether you already have the antibodies that attack Rh-positive blood. (You could have them even if you miscarried the baby, had an abortion, or had an ectopic pregnancy.)
If you do have the antibodies, it's too late to get the shot, and if your baby is Rh-positive, he's likely to have some problems. If you don't have the antibodies, then the shot will keep you from developing them.
What are the chances that my baby and I are Rh-incompatible?
If your baby's father is Rh-positive — as most people are — you have about a 70 percent chance of having an Rh-positive baby. So if you're Rh-negative, it's likely that you and your baby are Rh-incompatible. In fact, your healthcare practitioner will assume you are, just to be safe. There's no harm in getting the Rh immune globulin shot, even if it turns out that it wasn't necessary.
Of course, if your baby's father has been tested and found to be Rh-negative, too, then your baby will also be Rh-negative and you won't need the shot. But if your baby's father is Rh-positive (or you don't know whether he's positive or negative), you won't know your baby's Rh status for sure until her birth unless you have an amniocentesis, a test that examines fetal cells from the amniotic fluid surrounding the baby in your uterus.
On the other hand, if you're Rh-positive and your partner is Rh-negative, you might have an Rh-negative child. Despite this difference, there's no need to worry, because it's extremely unlikely that your baby will be exposed to your blood and develop antibodies. It almost always happens the other way around.
How could my baby's blood leak into mine?
Normally during pregnancy, your baby's blood stays separate from yours and very few blood cells cross the placenta. In fact, your blood is not likely to intermingle in any significant way until you give birth. That's why Rh incompatibility is usually not a problem for your first baby: If your blood doesn't mix until you're in labor, the baby will be born before your immune system has a chance to produce enough antibodies to cause problems.
However, you'll need a shot after the birth if your newborn is found to be Rh-positive. If you were exposed to Rh-positive blood during delivery, the shot will prevent your body from making antibodies that could attack an Rh-positive baby's blood during a future pregnancy.
(Your delivery team will take a blood sample from your newborn's heel or from his umbilical cord just after he's born to test for several things, including Rh factor, if necessary.) Without treatment, there's about a 15 percent chance that you'll produce antibodies,but with treatment, the chance is close to 0 percent.
Since a small number of Rh-negative women (about 2 percent) somehow develop antibodies to their baby's Rh-positive blood during their third trimester, you'll also be given shot of Rh immune globulin at 28 weeks that covers you until childbirth. And you'll need a shot any other time that your baby's blood might mix with yours, including after an invasive procedure, such as an amniocentesis or chorionic villus sampling (CVS), or if you have:
- a miscarriage
- an abortion
- an ectopic pregnancy
- a molar pregnancy
- a stillbirth
- an external cephalic version (ECV)
- an injury to your abdomen during pregnancy
- vaginal bleeding
If you find yourself in any of these situations, remind your caregiver that you're Rh-negative, and make sure you get the shot within 72 hours.
How does the shot prevent me from developing antibodies?
The Rh immune globulin shot consists of a small dose of antibodies, collected from blood donors. These antibodies kill any Rh-positive blood cells in your system, which seems to keep your immune system from developing its own antibodies. The donated antibodies are just like yours, but the dose isn't large enough to cause problems for your baby.
This is called passive immunization: For it to work, you need to get the shot no more than 72 hours after any potential exposure to your baby's blood. The protection will last for 12 weeks. If your practitioner suspects that more than an ounce of your baby's blood mixed with yours (say, if you've had an accident), you might need a second shot.
You'll get the injection in the muscle of your arm or buttocks. You may have some soreness at the injection site or a slight fever. There are no other known side effects. The shot is safe whether your baby's blood is really Rh-positive or not.
What will happen to my baby if I develop the antibodies?
First, keep in mind that this is highly unlikely if you're receiving good prenatal care and are being treated with Rh immune globulin when necessary. Even without treatment, your chances of developing the antibodies and becoming Rh-sensitized are only about 50 percent even after several Rh-incompatible pregnancies.
If you didn't get the shot, though, and you became Rh-sensitized and your next baby is Rh-positive, he would probably develop Rh disease (hemolytic disease). Your antibodies would cross the placenta and attack the Rh factor in your baby's Rh-positive blood as if it's a foreign substance, destroying his red blood cells and causing anemia. The disease can cause problems ranging from severe newborn jaundice to brain damage or, in extreme cases, miscarriage or stillbirth.
Once you're sensitized, you have the antibodies forever. And you produce more with each pregnancy, so the risk of Rh disease is higher for each subsequent baby. While healthcare providers try to screen and treat as many women as they can reach, about 5,000 babies develop Rh disease in the United States every year.
The good news is that doctors are finding new ways to save babies who develop Rh disease. Your practitioner can monitor your level of antibodies and keep tabs on your baby's condition during pregnancy to see whether he's developing the disease. She may check on the condition of your baby's red blood cells using Doppler ultrasound or amniocentesis.
If he's doing well, you might be able to carry him to term without complications. After birth, he may be given what's called an exchange transfusion to replace his diseased Rh-positive red blood cells with healthy Rh-negative cells. This stabilizes the level of red blood cells and minimizes further damage by antibodies circulating in his bloodstream.
Over time these Rh-negative blood cells will die off and all your baby's red blood cells will be Rh-positive again, but by that time, the attacking antibodies will be gone.
If your baby's in distress, he might be delivered early or given transfusions through the umbilical cord. The survival rate for babies who receive a transfusion in utero is as high as 80 to 100 percent, unless they have hydrops (a complication caused by severe anemia), in which case the chances of survival are about 40 to 70 percent.