As the latest pregnant famous person to do their best Demi Moore Vanity Fair cover impersonation, topless former Tiger Woods mistress Rachel Uchitel showed off her growing baby bump -- and nearly everything else -- in a sexy maternity g-string.

This is baby's first thong.

The 37-year-old -- who is due in eight days -- then went a little more demure by also posing covered up in a sheet.

Uchitel -- who's married to former Penn State football player Matt Hahn -- knows a new mother needs to set a good example.