Thailand's baht, however, hit a three-month high as the government lifted a state of emergency in Bangkok, taking a step to restore some confidence as anti-government protests subside.
The Philippine peso fell to its weakest level in nearly five weeks on bond outflows and corporate dollar demand.
The South Korean won eased on dollar bids from offshore funds and local importers. Indonesia's rupiah edged lower as importers bought dollars for payments.
The yuan fell beyond 6.20 per dollar for the first time since April last year amid market speculation the central bank will keep the currency weak as economic growth slows.
The Fed is widely expected to continue reducing its monthly bond purchase programme by $10 billion, but also to alter its forward guidance in its policy statement later on Wednesday. The policy review is the first to be presided over by new Fed Chair Janet Yellen.