guyshahar - I understand what you are saying about the GPs response but I still would urge you to get tested so that your wife does not needlessly receive anti-D if you are rhesus negative. The NICE guidance that all doctors and medical staff have access to does support this option.
I am an example of why women are being offered anti-D during their pregnancy. When I was 37 weeks pregnany with my second child it was discovered that I had developed anti-D antibodies. When I thought about it I had experienced some abdominal pain at 34 weeks which passed itself within a few hours. It is likely that I had a very small bleed from the placenta at that time and blood was able to mix which allowed antibodies to form. However, it wasn't sore enough for me to go to the doctor, and even if I had it is unlikely that this blood mix would have been suspected.
Anti-D needs to be given within 72 hours of an episode of bleeding or suspected bleeding.
I was induced at 39+6 weeks because of the presence of antibodies and my son was nursed under phototherapy as a precaution for 3 days though he did not actually become jaundiced.
Once antibodies have developed they are always there. My husbands blood group was checked when I became pregnant for the third time. It was checked to see whether he was hohozygous positive which meant that all our babies would have a positive blood group or heterozygous positive where the baby could be positive or negative. My DH was honozygous so we knew throughout the pregnancy that the baby would be positive.
The first affected pregnancy and cause a severe antibody reaction which means that the baby's red blood cells are attacked by the antibodies.
I didn't have a severe reaction but the antibodies started to rise at 30 weeks. I was induced at 35+4 weeks and my DS needed to be ventilated because of prematurity. He was nursed under phototherapy for a week and came home at 2 weeks of age. At 6 weeks old he was found to be anaemic and needed a blood transfusion (76ml). The anaemia happens because the maternal antibodies are still circulating in the baby's system for weeks after birth. He was then fine and is now 18 years old.
I then had a miscarriage which was not antibody related.
I then had my fourth child and she was induced at 37 weeks. Tests were done by ultrasound every month to look for signs of developing anaemia. She was nursed under septuple phototherapy (7 times normal) and needed 3 exchange blood transfusions in the first 48 hours of life. She was on folic acid till 12 weeks of age and she had regular blood tests till she was 12 weeks when the anaemia she had corrected itself.
Anti-D injections coat any baby blood cells that are present in the maternal circulation so that the mothers's body does not recognise them to then form antibodies.
So in answer to your question, once you have antibodies they are always there and subsequent pregnancies are affected more. Anti-D injections are not given when you have already developed your own antibodies because the damage is done.
In the past anti-D was given where there was a suspicion of a sensitising event such as abdominal trauma, threatened miscarriage, following amniocentesis. The problem is when a sensitising event is not recognised which happened to me. This is very rare though.
I personally have a concern that all women get anti-D despite this being a rare occurance and who knows what the future will reveal.
THis is why I am urging you to find out your blood group.
Good luck with whatever you decide.