Hey, congrats on making it to 30 weeks! I think it's definitely worth asking your gynae about HL, especially since you're already flagged as high-risk, many mums I know have gotten it approved, though honestly it really depends on your individual doctor and how they assess your situation at the time.
From what I've heard, NUH gynae can be a bit stricter than private practice when it comes to issuing HL, so you might need to build a stronger case around the pre-eclampsia risk and how stress could affect that rather than just burnout alone, your doctor will want to see a medical reason that justifies the leave. I'd suggest being honest with them about what you're experiencing at work and ask directly at your next appointment; some consultants are more supportive than others, so if the first person isn't keen, don't be shy about raising it again or asking another doctor in the clinic.
The good news is you're still early enough to plan this properly with them, and they know your medical history well since you've been going to the high-risk clinic. Just go in with a clear conversation about your concerns and see what they say, worst case they'll give you partial HL or recommend something else that might help.