The most likely time a woman with a regular 28-day menstrual cycle can conceive will be at approximately the 14-day or mid-cycle mark, according to WebMD. Abnormal menstrual cycles may happen for a variety of reasons, and repeated irregularities should be mentioned to a physician. according to the Mayo Clinic.
WebMD advises that ovulation for most women occurs in the middle of the menstrual cycle, the average of which is 28 days. This 28-day average puts the most likely time for conception at two weeks prior to the first day of menstruation.
The regularity of menstruation can vary widely for many different reasons. The beginning of the menstrual cycle during puberty can be the cause of irregular menstruation. So can the onset of menopause and a pregnancy or miscarriage. Some women are able to regulate their menstrual cycles through the use of oral contraceptives or birth control pills. Irregular menstrual cycles may also be a sign of more serious health problems, including pelvic inflammatory disease, endometriosis and eating disorders. The Mayo Clinic advises consulting a physician with any concerns about irregular menstrual cycles to rule out any health concerns.