I just recently saw that hilarious movie Knocked Up, and I wanted to set something straight. When the guys were talking, one of them said something about how everyone knows that a girl can't get pregnant if she's on top while having sex. According to his belief, gravity makes sure the sperm doesn't get to the egg.
Ladies, listen up, if you didn't already know this, he is completely incorrect. Anytime a man ejaculates inside a woman, the semen goes into her vagina and those sperm use all their might and determination to swim upstream. If even just one of them gets to your egg to fertilize it, boom — you're pregnant regardless of what position you have sex in. Unprotected sex can equal unplanned pregnancy.
If you're not ready to be a mom, use a consistent and effective form of birth control (the Pull and Pray Method is not a good option). Using condoms, an IUD, or hormonal birth control such as the pill or NuvaRing are great options. Find what works for you and stick with it.