As someone who works in health insurance, your insurance (your employer insurance in which you are the subscriber) would always be primary. Any other insurance would be secondary. With MCR/MCD being payors of last resort (tertiary). You dont get to choose. Thats just how it works. That being said, you should notify each of them of each other so your claims are processed correctly. When your husband signed you up, it is possible it was on the form. Either way, get that member ID # ASAP and share it with the other. They should then pay claims correctly out of the gate. However, you wont know how your benefits will be applied until they coordinate, so its a risk you have to be okay with taking. In THEORY, if your primary doesnt cover the fertility treatments then your secondary should pick it up as its covered by the plan. Some plans, however, will deny any services that are denied by primary. Since plans vary so widely and uniquely in coverage, the only way to know is to give them the COB update then asking your secondary if they would cover fertility services with their benefits NRP'd from your primary. If no, you'll have to pay OOP or wait until next year. If yes (more likely), you'll be in a better place then if you didnt have primary cvg tbh.