Who was the only "big four" character on "The Big Bang Theory" to become a father during the show's run?

At the risk of sounding sexist, or being accused of gender baiting by someone of the Post Office, the word is spelled "male", not "mail".

Brilliant series. We keep watching the repeats and laugh even though we know what's about to happen.

I’m pretty sure all five main characters were on every episode of the show.

None of the four men is a mailman. They are, however, MALE men.