Hello! I know alot of people have answered questions for you but I work in transfusion so may be able to shed a little more light on it (and this may get a little long)
The problem occurs when your baby is RhD positive because you are RhD negative. During pregnancy your baby’s blood can ‘leak’ into your own – normally thats not a problem as it is not enough to initiate an immune response. The problem occurs when large numbers of baby red cells cross into the maternal blood stream, usually this only occurs during labour but sometimes abdo trauma or miscarriage can cause this as well
If your baby is RhD positive, your immune system then recognises the RhD present on the baby cells as foreign and creates antibody known as Anti-D. During a first pregnancy a larger form of anti-D is formed (known as IgM). IgM anti-D is unable to cross the placenta, so that first baby is most likely born healthy, especially if the bleed occurs later in pregnancy or at labour.
In subsequent pregnancies, if the baby is RhD positive, your immune system recognises the normal small leakage of foetal cells and ‘remembers’ the foreign RhD. Because of this, it produces Anti-D again – but this time in a form known as IgG. IgG anti-D CAN cross the placenta and thus the disease occurs (the destruction of the babies red cells, leading to a built of break down products that can lead to jaundice, anaemia etc).
In your case, due to your miscarriage, you were adminstered Rhogam. This is to mop up any foetal cells in your circulation before your body can recognise it and produce anti-D. Depending on how far along you were along at miscarriage can alter how much foetal cells actually passed into your blood stream (they may not have even be enough to cause sensitisation), and also the foetal cells may have inherited your blood group and not have caused a problem at all (it is impossible to say). The reason why Rhogam is adminstered at around 25 weeks and after delivery is because these are the key times that bleeds occur and cause sensitisation – Rhogam then covers the pregnancy from 25 weeks (it stays active for a long while) and the extra given at delivery mops up any cells from labour. Unfortunatly without performing your testing myself I cant give you any idea of whether or not you have a significant enough bleed to cause sensitisaton.
In regards to future pregnancies, any baby that inherits your blood group will have no issue at all even If you have developed anti-D. If you have developed anti-D, you will have antibody titres done to determine how Anti-D is in your blood stream as there is a cut off for safe levels. This will be checked during any future pregnancies to ensure the best outcome for you and baby.
Sadly they will be unable to check your blood currently because of the Rhogam (which will give you a false positive). Most likely, you will have to come back for a blood test at a later date to confirm whether or not you have developed Anti-D.
Wow this was long, sorry about that. Good luck talking to your doctor and in the future.