When does the gender of the baby get decided?

I have come to believe that the gender, appearance and life state of the child is determined at the moment of birth. This is something I stumbled upon by accident. I had a couple conceive a child. During the pregnancy, the father was bitten and turned into a vampire. Mysteriously, the child was then also born a vampire. This leads me to believe that the game performs its genetics checks upon birth rather than at conception, which also allows for the player to eat foods and listen to music during the pregnancy to influence gender.