[MichaelG]

Originally Posted by neverending

Yes, you missed it. From the wikipedia entry on the film:

A few weeks later, Rosemary learns she is pregnant and is due on June 28, 1966 (6/66).

And:

At the Castavets' New Year's Eve party, Roman raises an equally cryptic toast: "To 1966: the Year One." Rosemary sees that Hutch has marked photographs and passages in the book. Using the clue given to her in the cryptic message, Rosemary deduces that Roman Castevet is really Steven Marcato, the son of Adrian Marcato, a former resident of the Bramford who was accused of being a witch and of worshiping Satan, and was a martyr to the cause

This source contradicts your source.

The 666 connection? The baby is born in the year 1966… in August. Seems odd the filmmakers would miss the obvious choice of birthing the baby in June, the sixth month, to complete the unholy triangle, but apparently Polanski didn’t feel like playing the numerology game… or did he?

www.movie666.com/top-666-movie-list