Egg production and ovulation occurs regularly. Usually, if a woman is menstruating regularly, she will be ovulating. But, this is not always true. A woman can be oligoovulatory (irregular ovulation) or anovulatory (no ovulation) and still have periods.
However, under such circumstances, her periods are generally either irregular (oligomenorrhea) or absent altogether (amenorrhea). As a result,she may require a number of tests to determine ovulatory status.