(I'm sure I read a mention somewhere that there is a vanishingly small chance that an act of Woo Hoo will result in a pregnancy, but I can't find it now.)
2. If you want a boy, eat apples during your pregnancy. If you want a girl, eat watermelons. Eating three of either is usually enough to do the trick.
According to Carl's Guide, your Sim has to eat the fruit BEFORE they are visibly pregnant. In other words, scarf those fruits within 24 hours of hearing the tell-tale lullaby jingle in bed. (I haven't tested this myself, but Carl knows his stuff!)