An Rh-negative mother's first Rh-positive baby is usually safe, but a second one is at risk. Why?
During the first delivery some Rh-positive fetal blood leaks into the Rh-negative mother, and she begins making anti-Rh antibodies -- but too late to harm the first baby.
During the first delivery some Rh-positive fetal blood leaks into the Rh-negative mother, and she begins making anti-Rh antibodies -- but too late to harm the first baby. Those antibodies persist. In a second Rh-positive pregnancy they cross the placenta and attack the fetal red cells, causing erythroblastosis fetalis. That is why the first child is usually safe while later ones are endangered, and why an anti-Rh injection is given after the first delivery.
Key point
The mother is only sensitised at the first delivery, so her anti-Rh antibodies threaten the SECOND Rh-positive fetus.
Common mistake
thinking the first Rh-positive baby is the one at risk.
Memory tip
first pregnancy sensitises, second pregnancy is attacked.
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