If you or your partner have ever thought that wearing condoms that fit tightly will prevent pregnancy better; that it'll stop sperm from getting out, you're wrong. This is a huge misconception, and could actually cause an unwanted pregnancy. You see if the condom is too tight, the friction of having sex could actually break the material.
Polyurethane and latex condoms are already 85 percent effective at preventing pregnancy, so if used correctly, you can't make them any more effective (unless you use them with another form of birth control such as the NuvaRing).
It's also important to remember that when a guy puts on a condom, he needs to leave a little space at the tip so when he ejaculates, there's room for the semen inside the condom. If it's is pulled on too tightly, it could get overstretched and cause the condom to break, or sperm could overflow out the top. Be sure to follow the directions on the box when using condoms, and make sure the guy always wears the correct size.