But DY, Avrohom and Sora were 90-100 when they finally had Yitzchok. Rivka and Yitzchok are told to be daavening in the corners of their home after 20 years of marriage and there was a possibility of divorce because she had not had children after 10 years of marriage (they waited 10 years for her to be ready to have children and then another 10). Leah daavened that Dina be a girl rather than the boy she was supposed to be because she knew that if she had 7 boys then Rochel would not even have had as many sons as the shifchos.
So although they did not have medical intervention, they merited to have clear nissim (especially since Sora did not even have a rechem, so how could she get pregnant).
Although I would hate to say no to an otherwise great shidduch, I can surely understand why OP would want her son to avoid a situation where the chances of not having children or needing large amounts of money to pay for treatments in order to conceive, etc. We all have nisyonos, but you don’t ask to have them given to you.