Rh, Fetal Anemia, and RhoGam
Your antibodies to Rh-positive red blood cells last a long time. In fact, they last long enough and are small enough to be able to pass through to your next baby, and they will do just that. As stated above, the ABO allergic reaction is mild. But if you’re Rh-negative and your last baby was Rh-positive, you’ve made anti-Rh antibodies. And you’ll be sending those anti-Rh antibodies through the placenta into your next baby. The fetal red blood cells that house the Rh-antigen will be attacked and over time your baby will lose these blood cells, becoming anemic. This isn’t good in a baby who’s trying to grow and mature. Such anemia can cause swelling reactions in the baby’s abdomen and eventually can cause serious injury or fetal death. This condition is referred to as "erythroblastalis fetalis."
The prevention of erythroblastalis fetalis is another victory of modern obstetrics. The condition is rare today because we give an injection soon after delivery, called RhoGam, to first-time Rh-negative mothers of Rh-positive babies. These are the mothers who we know will be making antibodies to their subsequent baby’s blood. RhoGam is also an anti-Rh-positive antibody. For moms who receive RhoGam, their bodies are fooled into thinking there's already been an adequate response and make no antibodies on their own. So now the antibodies of RhoGam don't attack subsequent babies because they're much bigger molecules than what you would have produced on your own and can’t pass through the placenta to your next baby. It’s this preventative measure that has so greatly reduced the risk of erythroblastalis fetalis.
But what if you’re Rh-negative and didn’t get this RhoGam shot after your last baby? If the last baby was also Rh-negative, there was no antigen-antibody conflict and all is well for your next baby. In fact, hospitals routinely check your newborn’s blood type and if your baby is Rh-negative like you, there’s no need to get the RhoGam shot at all. But if you’re Rh-negative and your baby were Rh-positive and you didn’t get the shot, the shot didn’t work well (almost unheard of), or was given too late to prevent you from making antibodies (there’s about a three-day window), then your next baby may be at risk of severe anemia as your antibodies cross the placenta barrier and begin attacking his or her red blood cells.
How can you tell if a baby is getting anemic from such a condition? If your history suggests such a risk or if telltale signs on ultrasound suggest erthroblastalis fetalis, an amniocentesis can be done. This is a technique in which amniotic fluid around your baby is withdrawn with a thin needle under ultrasound guidance and is then studied. In cases of erythroblastalis fetalis, the fluid becomes murky. This is because there’s a lot of bilirubin in it, which is a breakdown product of exploded red blood cells. By this method it can be determined how serious the condition is.
The Best News of All
In the past, babies with erthroblastalis fetalis were just out of luck. Such a pregnancy often resulted in a “stillbirth,” a vague term at best. A wide range of unrelated conditions, from genetic malformations to umbilical cord knots, could all result in stillbirths. The Rh factor was identified in 1940. In the mid 1960s, the RhoGam shot was developed and began being clinically tested. At that time, 14 percent of Rh-negative mothers developed antibodies to their subsequent babies. Doctors started giving RhoGam routinely by the late 1960s, and soon, the chances fell to 1.8 percent. But even the 1.8 percent was too much. So now RhoGam is given not only after delivery, but also at 28 weeks gestation—well before delivery. This early treatment is in case there is some "silent" bleeding—too scant to be noticed, but enough to develop antibodies during a current pregnancy. Now the 1.8 percent has been reduced to 0.07 percent (less than one in a thousand).
That is why today almost all Rh-negative concerns during pregnancy can be relieved. And usually it's as simple as A-B-C…and a little RhoGam.