if you masterbate before sex will it decrease the chances of the girl getting pregnat?
NO! I dont want to sound overbearing but NO! Sperm is just as potent wheter u masterbate before sex or not. Also, considering you asked this question I feel obligated to tell you that pulling out also does not significantly decrease the chance of getting a girl pregnant either. A little survival mechanism we picked up a few thousand years ago which today goes by the name of "pre-cum" developed in humans. It serves 2 purposes: 1) lubrication and 2) for men that have trouble with orgasms. Because of this second reason precum contains actually more sperm than that of an actual orgams. Thus, although you may keep the white stuff out, pregnancy can and will happen. (No Joke). So do yourself a favor and wear a condom.