Dear jsbla: This is a breast cancer forum but your question is not terribly complicated so I will answer. CA-125 is not a screening test. It is also not diagnostic. It is often done when ovarian cancer is diagnosed (in surgery) so that the response to subsequent chemotherapy can be measured. The only role for CA-125 in ovarian cancer is to track the disease AFTER diagnosis. If your mother did not have surgery or did not choose chemotherapy, there may have been no real reason to do the test. In other words, in untreated ovarian cancer, you would expect this level to be elevated. If you are not going to use the number to evaluate the response to chemotherapy, then there is no real reason to collect the information.
Some forms of ovarian cancer are considered hereditary - usually those diagnosed in younger women. However, if your mother had ovarian cancer, there would be a slightly increased risk for her sisters or daughters. This information should be shared with the respective gynecologists who can recommend appropriate screening. At most, a pelvic ultrasound may be ordered at certain intervals in addition to the standard pelvic examination. A CA-125 should NOT be done for screening.