Alamak don't stress too much lah, you still got options! My friend went to check with her AIA agent when she was diagnosed with GDM around the same time as you, and the agent told her that some policies can still cover you but the GDM might be listed as an exclusion, so the coverage is a bit limited, still better than nothing though! Best to call a few agents directly and ask them point blank, faster than guessing, and they'll tell you honestly what can still be done at week 28!