1. Because women are only fertile for a few days a month. And some months, women never ovulate at all, or the ovum is not in good condition.
2. Because it's really really really hard for sperm to get to the egg. (Most of them never even make it through the cervix.)
3. The zygote doesn't implant, or dies after a few days. This probably happens a lot more than people know since it will happen before pregnancy can even be detected.
4. God says "No way Jose!" and prevents it.
In a year of unprotected sex between a woman and her man, only about 70% or so will have a pregnancy - if they are of peak fertility age and otherwise healthy and able to conceive.
Basically, every act of unprotected sex is a game of Russian Roulette. You never know which time the pregnancy is going to happen. It's a very foolish game to play.
5. His sperm are crap.
There's approximately only 6 day in a cycle where a woman can get pregnant, those are the five days leading up to the ovulation and about 1 day after. Sperm can live up to 5 days inside a woman's body meaning if you don't want to get pregnant you can have unprotected sex between the 2nd day after and 10 days before an ovulation, however I wouldn't take those numbers too exact these things can vary!!!
Simple. You need one egg and one sperm to get one fertilised egg. Doing that is somewhat complicated in and of itself,
BUT you need more than simply a fertilized egg. The egg must be *viable* when the genes hook up, they do not always hook up correctly. The egg may not be able to replicate. If it is able to replicate, it may not *pass* the mother's quality control checks. If it can replicate and it does pass the checks, it may not implant in time.
If it does implant in time, it may not express the hormones needed to ensure that the pregnancy progresses OR the mother's body may not react to the implantation.
Oh it's not that easy to get pregnant. If a woman could get pregnant every time sperm ends up inside her, world population would be 70 billion instead of 7 billion.
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What's Your Opinion? Sign Up Now!maybe when his sperms are having problems or they are defected or something
She might not have eggs to be fertilized.
The odds of conception are less than 50% and they are lucky.
It's not guaranteed. It's not as easy as movies would portray it, especially not for everyone.
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