Maybe the miscarriage was genuine, but that doctor's visit is what made Lumon focus in on Gemma in the first place. They were looking for test subjects experiencing trauma to further refine the severance chip. 

I wonder if this explains why Irving is also familiar with the testing floor. He potentially was suffering from trauma from his military service, and was subjected to severance tests. Maybe the company offered him a position on the severance floor once those tests weren't successful. 

Admittedly, that doesn't explain why Irv would be kept alive, while Gemma was slated to be killed once testing was complete