Kate93

Welcome to the forums.
You don't indicate which WLS you've had which can change how such could impact pregnancy.
I don't have experience with Kaiser. Nor do I have experience with pregnancy after WLS.
I'm just here to keep you company while you are waiting for the informative replies that are soon to show up shortly. In the meantime... how about a little chit-chat?
I can completely understand insurance wanting to ensure you are supported if you've had any of the malabsorption surgeries (RNY, DS). It's important that everyone involved understand this aspect of surgeries and how you will have to compensate for the health of your fetus.
If you've had a restrictive surgery (RNY, sleeve, most current varieties of DS [I'm told]), then it is a matter of getting all the standard and special nutrients that are hard to achieve when one is eating small volumes of food. Effectively, you will have to figure out how to eat around your surgery now through a couple years post-pregnancy without continuing it when you don't want to.
So, speaking with a dietician, though I would go for a nutritionist, would be a monthly meeting well worth going forward with even if you keep all your benefits if you opt-out. Once the meetings get repetitive and you are not getting anything out of them then you might consider opting out.
Be careful if they say it's OK to opt-out. Be sure you clarify that an order of 'opt-out is up to you' does not come with a side of 'we won't cover pregnancy costs we think are related to WLS."
Good luck,
Tek