In the absence of getting a shot of RhoGam Anti-D at the time of first trimester miscarriage, are all Rh negative women equally likely to become isoimmunized, or is there less risk if she was 5 weeks pregnant vs. 6 weeks vs 7 weeks vs 8 weeks, etc.?
The Rh antigen was found on the RBC membrane only in the sixth week. As antigens of the Rh system are exclusively erythrocytes, I believe that the risks of alloimmunization start from this moment on.
But The heart and major blood vessels begin to develop earlier—by about day 16. The heart begins to pump fluid through blood vessels by day 20 which is 5 weeks . Any comment?