Actually to be quite honest sex before marriage isn't the best choice, and I am willing to give reason to this. 1) You may contract STDs or even spread them along the way if you do end up having sex with a variety of partners, you never know if somebody is lying to you or not. 2) From my perspective, and yes, this is opinionated, I feel that you should lose your virginity to somebody that hasn't taken dozens of others' virginities away as it won't be quite so special. 3) Studies have shown that sex before marriage has caused more stress to the couple. 4) You could get somebody pregnant or even be pregnant, depending on the gender, obviously. 5) You won't be quite so emotional about the whole thing if you're caught in the act and you are married (provided you are with your spouse in this event...and not cheating, however you're most likely to be very embarassed, and the people who walked in on you will be incredibly disturbed)
And just to clear things up: this is where laws don't prevent your marriage. I know that gay couples can't get married everywhere, and they can't get pregnant, however I can't defend them on the STDs.
Never said marriage did prevent them, but yes, you should get tested as well as your partner. However statistically speaking you get more sex and less stress if you do manage to get preggers after marriage.