Most women have about 12 periods per year. Stress, intense exercise, and sudden weight loss or gain can cause menstrual irregularities. The more irregular your cycle is, the harder it becomes to predict ovulation.
In a regular 28–30 day cycle, the fertile days are between days 12 and 16. If your cycle is longer than 35 days, your gynecologist should evaluate you to check for other possible causes, such as polycystic ovary syndrome (PCOS), ovarian dysfunction, thyroid disorders, or high prolactin levels.
