At 37 weeks with your history of one preterm baby, I'd honestly lean toward starting your break sooner rather than later, someone in my mum group mentioned that for third babies especially, things can move faster, and you don't want to be caught rushing. The good news is that for your third child, you're entitled to 16 weeks of Government-Paid Maternity Leave, and you can choose to start it up to 4 weeks before your due date, so taking leave around now is perfectly within your rights. Some mums prefer to save all the leave for after birth to maximise bonding time, while others (especially with an unpredictable history like yours) feel the peace of mind before delivery is worth it, both are valid, it really depends on how you're coping physically. As for the hesitation, I think a lot of us feel that guilt about "leaving" work, but your body and your baby genuinely do come first here, especially at this stage.