I've heard women mention 'im safe' this week.

I know about sperm for lubrication, pre ejaculation, and there's always a risk of STD and pregnancy, etc.

Ive gathered that a 'safe week' has something to do with the egg. Is this before a period, because the blood and egg have expired from not being fertilized, or after a period because the egg hasn't settled to be fertilized? I know its just a lesser chance, and not necessarily a 100% safe, but what makes it a 'safe week' to have unprotected sex?

Oophorectomy.

Vasectomies can heal.

Edit: My wife reminded me of one other way - when she's already pregnant.

The so called 'safe week' probably originates from the Roman Catholic rhythm method. Since catholics are banned from using 'unnatural contraception' this was an attempt to limit the family size using so called 'natural birth control methods'.

Bear in mind two things though;

The catholic church also teaches that sex is for the purpose of making babies and attempts to thwart that process are against God's will - so how serious do you think the teaching on contraception is in terms of preventing babies? It's meant to lessen the odds a bit to give those Catholic moms a bit of a break but...

Most catholics cheat. Have you even seen the size of a catholic family that sticks to it by the letter? My friend's mum did - she had 13 kids...

I could go into the theory of when it is supposed to be safe and why but this method is so ineffective I aren't going to promote that sorry.

Next time a woman tells you she is 'safe this week' only accept her word if you are prepared to spend the next 18 years paying paternity.

And bear in mind that any woman who protects herself from pregnancy so ineffectually isn't protecting herself from STDs either. I know you are aware of STDs but a woman who says it is her 'safe week' is probably in the HABIT of not using condoms..