I just found out about this SWEET resource.
The Gay & Lesbian Medical Association (GLMA -- they call themselves GLAM. 'cause they're just that gay.) has a resource to search for LGBT-friendly providers. You can narrow by gender, specialty (including ob/gyn), etc within the Boston area.
Their website:
http://www.glma.org/And a direct link to their directory:
http://glmaimpak.networkats.com/members ... ovider.aspA search for female ob/gyns in Boston returned 4, but you may want to search by zip -- the city search doesn't include the outskirts of Boston.