Art,

I just looked it up in the dictionary.

The term more properly transliterated from the Hebrew would be: bath miswah. For some reason the common spelling is either Bas Mitzvah or Bat Mitzvah. It lists both Bas & Bat as "common" In Hebrew the 'h' is pretty weak, so I guess the pronunciation is kind of inspecific.

Since Semitic languages don't have as strong vowels as other languages, it is difficult to transfer the spelling from Hebrew or Arabic alphabets into the Roman alphabet.