Chances of getting pregnant?

In my Sims game.. along with their family club running constantly which includes Flirty and Woohooing.. and all of the flirty things in the house.. my human couple doesn't woohoo, unless I make them.. but my vampire couple .. is another story.. they have gone on their own a couple of times.. and I initiate it for them also using just Woohoo.. and well, lets just say a LOT.. lol.. they have beat that poor flowered bush down almost. But so far, Brisa has not became preggers.. On the other hand, I had my human couple, One and Teagan try for a baby just once, and she became pregnant. And something I noticed.. not sure if it was lag, or maybe something new within the Vampire expansion.. but when Teagan took her test.. and it did come back positive.. she did not get the first slight baby bump they always get when it registers positive.

Either way.. I would love if EA would put a small chance of pregnancy with just WooHoo.. but then players would whine and cry about it, just like they did with the freewill woohoo when EA snuck it in on us last year.