Which situation is most likely to result in a missed menstrual period?

A missed menstrual period is often indicative of a possible pregnancy, making it the most likely situation among the options provided. When a woman conceives, the hormonal changes that occur prevent the usual menstrual cycle from happening. The body produces human chorionic gonadotropin (hCG), which supports the pregnancy and overrides the signals that would typically lead to menstruation.

While hormonal birth control can also affect menstrual cycles by preventing periods or causing irregularities, this does not necessarily lead to a missed period in the way pregnancy does. Excessive exercise can impact menstrual cycles due to changes in body weight and stress levels, potentially leading to missed periods, but this is less common than the direct effect of pregnancy. Premenstrual syndrome (PMS) refers to symptoms experienced prior to menstruation, not a condition that causes periods to be missed. Therefore, pregnancy remains the most definitive cause of a missed menstrual period among the options listed.