Two Questions about Birth Control techniques - would like answers with source material?

I have specific question regarding two diferent birth control technique:
1) IUD - If this is placed *inside* the uteris how does it block sperm from reaching the egg? That happens outside the uteris, right?
2) IUD - regardless of the above answer, does an IUD work even if the egg *is* fertilized by sperm? If so, how? Does it "kill" the fertilised egg, or a short time ago "lock it out" from the uteris?

3) Cervic cap: Why do I see that this have between 79-93% (or whatever) success? If the cervic is closed, it's closed. Does the discrepency between these numbers and 100 enjoy to do with the percision that the device is used or is in attendance another factor?
Thank You
Answers:

Menopausal for 2 year..then a interval..HEAVY FLOWWhat would be the cause of this?

Both kind of IUDs work by preventing sperm from joining with an egg by affecting the passageway they move. The hormone in Mirena increases worth. It thickens cervical mucus, which provides a line that prevents sperm from entering the uterus. It also prevents some women's ovaries from releasing eggs (ovulation).

IUDs also alter the lining of the uterus. In view, this may prevent pregnancy by preventing the implantation of a fertilized egg — but this has not be scientifically proven.

Diaphragms, caps, and shields maintain sperm from joining the egg.

* They block the opening to the uterus.
* The contraceptive cream or jelly stops sperm from moving.

Fourteen out of 100 women who enjoy never been pregnant or given birth vaginally and use FemCap will become pregnant during the first year of typical use. Of 100 women who own given birth vaginally and use FemCap, 29 will become pregnant during the first year of typical use.

Protection may be increased by

* making sure the cervix is covered before respectively act of intercourse
* making sure spermicide is used as recommended
* using a latex condom

I, one-sidedly, have be on Mirena for a year now, and I love it. I would absolutely recommend it.