Apparently, halachic infertility is kind of a big deal:
forward.com/news/157819/for-some-halacha-makes-conceiving-tough/
The religiously approved solution seems to be medicating the heck out of the infertile women rather than budging on the number of days of no bleeding:
"Grazi said that he typically addresses halachic infertility by directing a patient to wear an adhesive patch that delivers estradiol, the natural female sex hormone, just as she begins menstruating. This patch is meant to delay her ovulation until after she goes to the mikveh. If the patch is working but the woman is still having trouble getting pregnant, then Grazi will add one of several medications to stimulate egg development — a potent one-two punch for toppling halachic infertility.
“But in the instances that the patch doesn’t delay a woman’s ovulation, Grazi will take more drastic measures, prescribing a medication called Lupron, which mutes the body’s egg development and ovulation. Then, Grazi will place a woman on a regimen of injectable natural hormones, managing her cycle so that her fertility peaks when she is allowed to have sex with her husband.”
“For halachically infertile couples with an aversion to using hormones, there are other options. One simple fix is to artificially inseminate the woman with her husband’s sperm before she goes to the mikveh. Since the woman is not allowed to have sex with her husband at the time that she is ovulating, insemination will bring his sperm in contact with her egg without the couple actually touching. Rabbis, however, disagree as to whether this is allowed under halachic law. Some Modern Orthodox rabbis are more lenient in their approach to insemination. But other rabbis, particularly those in ultra-Orthodox communities believe that insemination during niddah can cause spiritual harm to the child.”