Ebichan - wow your case sounds complicated. You are a Singaporean right? So erm I thought you would need to declare your marriage status even though you got married in Japan? I have no idea. You might need to do more research. Anyway Quincy is right - only married couples are allowed 4 months maternity - unless your company has an alternative policy.
Happilymarried - yes!!! very impt to check when doc goes on leave. Unless you are the sort who dont mind an alternative / replacement when doc is away. Have you checked with your doc?