Which of the following is a common sign of pregnancy?

A common sign of pregnancy is irregular periods, which can often be one of the first indications that a person may be expecting. During early pregnancy, hormonal changes can cause a temporary disruption in the menstrual cycle, leading to missed or irregular periods. This is due to the body preparing for a potential pregnancy and the production of hormones like human chorionic gonadotropin (hCG) that prevent ovulation.

In contrast, increased energy, weight loss, and high exercise tolerance are not typically signs of pregnancy. Increased energy may be associated with various factors unrelated to pregnancy, and it can sometimes occur in the early stages of pregnancy, but it is not a common sign. Weight loss is not a typical symptom of pregnancy; in fact, many people experience weight gain due to changes in appetite and metabolism. High exercise tolerance can vary widely among individuals and does not provide clear evidence of pregnancy. Overall, irregular periods are a key early indicator that can prompt someone to take a pregnancy test or seek medical advice.