If you are married, both have medical insurance and have children, you would follow the "birthday rule". The parent with the birthday that falls earliest in the calender year (no matter what the birthyear is) would be the primary insurance. For example. Mrs. Smith was born May 3, 1945 and has Blue Cross that she has carried for 15 years. Mr. Smith was born June 10, 1939 and has had Aetna for 20 years. The primary insurance would be Mrs. Smith's policy as she was born on May 3rd which comes before June 10th.

If both parents have the same birthday (it does happen), then you defer to the policy that has been in place the longest. So, if Mr. And Mrs. Smith had the same birthday month and day, then Mr. Smith who has had insurance for 5 more years than Mrs. Smith, would have the primary insurance policy.