Do find out more about the different insurance plans (Manulife, AIA, Qiren AIA, AXA) before deciding on the one that's most suitable. For us, we went with Qiren AIA. Most insurance companies would need the mummy to be minimally 12/ 16 weeks pregnant (I forgot) and below 32 weeks pregnant. But I'll say to buy earlier before the GD test cause most mummies may be rejected if they fail this test!
I rmb standalone maternity insurance is very little. Majority is tied to something. Maybe can check NTUC?