Why can't women conceive even if her menstrual cycle are normal?

Many reasons: A regular menstrual cycle doesn't preclude a woman or her partner from infertility. Many, many things can cause infertility without affecting menstrual cycle. To touch on just a few: female anatomical issues, endometriosis, anovulatory cycles, etc. Male partner may have low sperm count or low sperm motility. Fertility issues should be discussed first with ob. May need reproductive endo consult.