Does the fact of not following Nidah regulations have an impact on pregnancy or the lack of it halchically speaking?
Shalom Uverachah There are really two elements to this question. First, on a religious and metaphysical level we believe that the halachah is binding and must be kept. We also believe in the concept of reward and punishment and that one who follows the mitzvot will be rewarded. While it is true that this Divine reward may not be immediate and may not be obvious it does affect everything that happens to us. Second, on a biological level the optimum time for pregnancy is just before ovulation. A woman who observes the laws of niddah and separates from her husband before mikvah will often be having intercourse most effectively around the time of ovulation and thus raises the chances of pregnancy. Again, this is not the reason that we keep the mitzvot, they are Divine commandments that are eternal and must be kept in all circumstances, having said that they may enhance the chances for pregnancy. You can read in Rabbi Tendler's book, Pardes Rimonim, more on this subject. Kol Tuv