Aside from pregnancy, common reasons for a missed or late period include stress, low or high body weight, contraceptives, thyroid disorders and polycystic ovary syndrome, explains Healthline. Certain chronic illnesses, such as celiac disease and diabetes, can produce physiological changes that cause a woman's period to skip or be delayed.
High stress levels can cause fluctuations in hormone levels, which can affect a woman's menstrual cycle notes Healthline. Stress can also lead to weight changes that can result in abnormal periods. Certain birth control pills contain hormones that stop the release of eggs from the ovary, so women may notice changes in their menstrual cycles when either starting or stopping a birth control regimen.