It doesn't to any woman on this board who's on birth control. But I'm glad you asked me to look it up. According to the people that know, the pill is only 92% effective so out of 5 million women, 400,000 of them will get pregnant.
What you should have said here is 400,000 women stand a higher probability of getting pregnant.
http://www.plannedparenthood.com/pp2/portal/files/portal/medicalinfo/birthcontrol/pub-contraception-pill.xml
Keep in mind that information is not up to date as recent studies have shown that for up to 20% of women the pill might be completely ineffective. Studies have shown that women who have moderate to severe hormonal problems have the hormonal problems corrected while on birth control, so their ability to get pregnant isn't only unhampered, but it's actually easier to get pregnant.
My wife was on the pill for a couple of years to straighten out her period,so I'm a little familiar with that end of things.It didnot make it easier to get pregnant.It only put her back on the proper schedule so to speak.
So is having your sexual organs lopped off, but neither one are especially practical now are they?