Can a late menstrual period mean I am pregnant?

Hpt. Reasons for missed/late periods: low body weight, obesity, marked weight ^ or v, over-exercise, endurance athletics, breast-feeding, ^ stress, illness, eating disorders (bulimia or anorexia), anovulatory cycle (no egg released), travel, hormone irregularities, drug use, meds (i.e., birth control) or medical problems (i.e. PCOS). #1 reason is pregnancy.
Not always. There are a number of common causes of irregular cycles. Certainly pregnancy is one of these, but if cycles persist in being irregular, there are some blood tests and findings on exam that may explain them.