I'm concerned about potential discrimination

Any qualified physician may treat mental health issues. All M.D.s are authorized to prescribe medication including for mental health issues although most will defer to specialists. I am without knowledge of any law or regulation which prohibits your OB practitioner from opining about mental health issues. Although, I suspect that if the employer retained a mental health expert your OB would probably defer to your own mental health expert as well. You should meet with your employer. They have the right to counsel and/or direct you regarding your duties for work. Regardless of what they have done in the past, if you wish to keep this job you may want to consider meeting with them. If for no other reason than to ask them what else they need from you. They could suggest your consulting with an independent medical expert at the employer's expense. If they did so you may wish to prepare your own mental health provider with advance notice of same. This is not legal advice. We have no lawyer client relationship. But if you have been performing your duties well remotely, there appears to be no reason that you will not continue doing so in the future. Some employers feel or presume that some pregnant employees may not return to work after giving birth. Meeting with them may aleviate their concerns. Caring for a newborn is time-consuming and they may suspect that you will no longer devote the hours which most professionals have given during COVID working remotely. They may want assurance from you that you will continue doing the presumably great work you have done so far. I personally know several employees who are much more productive working remotely, partly because their mental health challenges were overwhelming in-person, pre-COVID, when they needed to work in a confined office. If your mental health expert believes that applies to you maybe discussing this now is a good option. If this employer intends to bring everyone back into the office, maybe that's not for you? But you need to assure them why that's necessary for you and how the employer will continue to receive outstanding or acceptable performance from you. If they believe your performance was not what they expected pre-pregnancy maybe this is the time to discuss accommodations which may have nothing or little to do with pregnancy. Good luck. Not legal advice. No lawyer client relationship. Accommodations are all about communication and give and take between employer and employee.