I've switched insurances 3 times since my pregnancy ended last Sept. (lots of job changes between DH and I.) All group work plans, from Cigna, to United Healthcare, to Anthem-MO, and now Anthem-VA. I'm also going through fertility treatments.
The only company I've had issues with so far is Anthem-VA, and that's because they've had trouble tracking all of my insurances last year (even though I gave them all of the information and have supporting documents, they are being a PITA and saying I have a "pre-existing condition exclusion for any treatment I received in the 6 months prior to the enrollment date, even though I've been covered by Anthem-MO even now and all 6 months prior.) Anyway, even though they are being a pain, in the letter they even acknowledge that pregnancy is not an allowable pre-existing condition.
So I think it generally should be okay, as long as you have been covered long enough (about 18 months) and haven't had a break in insurance for more than 63 days.
Now dealing with them may be a pain. Insurances suck.