I and my bf have same nadi (Madhya) we are committed and want to marry but parents don’t agree due to nadi dosh. What is the science behind it and what can be done to overcome this problem? Our blood groups are compatible i.e. both of us are Rh positive (he is O+ and I am A+)

Faith in Horoscope goes with your belief system. Except Hindus no one believes in horoscope matching for marriage and still life is on for them. I have seen numbers of couple with Nadi Dosh having normal healthy kids and without Nadi Dosh having no kids. It has no connection with medical science. You have to convince them by citing such examples.