That is right in the real world and as u said there are plenty of women who does that
(i don't know how much of them wants to get pregnant and raise their child since as u said it reminds them and makes them relive it most people give the child up for adoption, also after rape any survivor who gets treated at hospital is treated with post contraceptive pill along with counselling, atleast in my country..... sure it varies for marital rape/roleplay gone wrong
but Hiroko is underaged in that time IF she was raped so she would have needed proper medical attention regardless) but setting that real world problem aside...i don't think it applies for Hiroko in Blucat's world, maybe it applies when she was bullied and had suicidal tendencies before meeting the MC BUT after their relationship Hiroko becomes so much dependent on MC also much more confident which could be seen in the story, so she must have a strong reason hiding the truth from him and for keeping the child to raise her with MC, atleast that is my take on it. And MC as smart as he is did not suspect Hiroko might've been raped instead he still thinks she must have cheated on him. Besides the reason u stated is so obvious which is bad for the plot and Hiroko doesn't seem like a victim throughout the story...but who except Blue only knows, maybe u are right..we just gotta wait for it.