I just got this one, although at first I was confused as to how I got it. But then I remembered I had "tried for baby" with a lover a few sim days prior.
So heres how to get it easily as a male sim:
1. Meet a female and start flirting; make sure she's single because it takes more time and effort to have a married sim cheat.
2. Go to your home and repeat the flirting process until it says she finds you extremely irresistible.
3. Try for baby with her and listen for the jingle; if you hear it she's pregnant if not then try for baby once more.
4. Go about your business and a few sim days later you'll get the achievement.
You get the achievement without having to take care of a baby which could be helpful if you are working on other achievements as well.