Can a pregancy be considered a pre ex under HIPAA?
I have an employee of a small group (8 employees) that originally refused coverage at the open enrollment date (in April). She is now pregnant and wants to buy into the coverage.

Pregnancy is specifically excluded as a pre-ex condition under HIPAA.
However, pregnancy, in and of itself, does not constitute a life status change that might allow the employee to enroll under HIPAA's special enrollment period rights. Birth of a child would, but not an ordinary pregnancy.
Further, under HIPAA, it would depend on why she declined coverage in the first place. If she didn't feel she needed it at the time, the special enrollment period does not need to be extended.
If she had other coverage then lost it, well, then HIPAA would kick in and you can allow the employee to enroll.