The risk of this serious problem – called erythroblastosis fetalis or perinatal hemolytic disease by doctors – arises when the mother has the Rh negative blood factor and the fetus, positive. In this case, if the baby’s blood, for some reason, leaves the placenta and comes into contact with the mother’s body, she starts to produce antibodies that destroy the child’s red blood cells, and may even cause his death. This occurs because the fetus’s Rh positive factor acts as an antigen (a foreign body that stimulates the production of antibodies) when it comes into contact with Rh negative blood. “The mother’s body interprets the presence of the child’s blood as an invader, an evil to be eliminated”, says gynecologist and obstetrician Renato Chaim, from São Paulo. While the baby is in the womb, it is not possible to know its blood type. Therefore, a prenatal examination is necessary to check, from time to time, whether the mother has become sensitized to the incompatible blood of the fetus.
In that case, there is a vaccine against the disease – but it can only be applied a maximum of 72 hours after the mother’s body has detected the invasion of the child’s blood. During pregnancy, everything that goes to the fetus – like nutrients and oxygen – passes through the placenta, but the blood never mixes. There are situations, however, that can cause internal bleeding (see the sidebar). The greatest risk is precisely in childbirth. “If there is awareness and no test is done, the mother will develop the antibodies, which will be stored in the memory of her immune system. For the baby that has just been born, there is no problem. But, if the same woman has a second Rh positive baby, the chances of him dying in the womb are very high”, says Renato. The antibodies will attack your red blood cells, releasing hemoglobins which, deposited in the fetus’ organs, cause their destruction.
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If both parents are Rh negative, there is no danger. The baby will also have the negative factor, the same as the mother, and there will be no blood incompatibility problems.
If the father’s blood is positive, the chance that the baby will have the same blood type is 50%. Therefore, you need to be attentive. Prenatal examination is essential to avoid the danger of incompatibility
Threatened abortion
premature labor
Amniocentesis (a test that takes a sample of fluid from around the baby with a needle)
partial placental abruption
In childbirth, the placenta must be expelled naturally. If the doctor forces it out, it can cause the baby’s blood, which is in the placenta, to enter the mother’s body.