He's Positive, She's Negative: What's That Do to Baby?

He's Positive, She's Negative: What's That Do to Baby?

It''s always a good idea for any couple to think ahead and prepare forpregnancy, so Mom and baby can be as healthy as possible. When facing thepotential for Rh disease, as you two are, it''s even more important. You''llprobably want to educate yourselves about Rh incompatibility. And in any case,make sure you find a health-care provider who understands Rh disease, and withwhom it''s easy to communicate.

One thing is clear -- your baby will have type O blood. What''s not clear iswhether your baby''s blood will be Rh-positive or Rh-negative, and that''s whatmakes all the difference.

Rh disease of the newborn arises from incompatibility of the Rh factorbetween the mother and baby. It''s a bit simplistic, but you can think of the Rhfactor as a protein that is either present (positive) or absent (negative) onred blood cells. Exact percentages vary with race, but most people areRh-positive.

A woman with Rh-negative blood has nothing to worry about if her baby isalso Rh-negative, and a woman with Rh-positive blood need not worry at all.Problems arise only with Rh-negative mothers and Rh-positive babies. Usuallythe first pregnancy goes fine. It''s a subsequent Rh-positive baby who may be atrisk. The mother herself is in no danger.

Normally, maternal and fetal blood supplies don''t mix during pregnancy, butduring childbirth, some fetal blood may enter the mother''s system. If themother is Rh-negative and the fetus is Rh-positive, the woman''s immune systemresponds with antibodies to the Rh factor. The chances of responding, and thestrength of the response, increase with each Rh-positive pregnancy. In asubsequent pregnancy these antibodies cross the placenta and enter fetalcirculation. If the next fetus is also Rh-positive, the mother''s antibodiesdestroy fetal red blood cells. The baby may be born anemic or jaundiced, and insevere cases many fetuses have died.

Although treatments are available to save affected babies - includingtransfusing Rh-negative blood, sometimes even prior to birth - preventionobviously makes more sense. The trick is to block the mother''s immune systemfrom becoming sensitized to the Rh factor.

An injection of anti-Rh antibodies (widely known by the trade name RhoGAM)given to the mother soon after birth neutralizes any fetal blood cells in hercirculation before her immune system has a chance to respond. Subsequentpregnancies should be like the first, as if the woman was never exposed to theRh factor. That''s the theory, and quite often things work just thatsmoothly.

Now for some real-life complexities. RhoGAM is useless if a woman is alreadysensitized. Any pregnancy event with the potential for fetal-maternal bloodmixing can sensitize the mother. That includes certain placental abnormalities,tubal pregnancy, miscarriage and invasive procedures such as abortion oramniocentesis. The chances of mixing and sensitization are lower earlier inpregnancy, but there''s still a risk.

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