Contraception methods should prevent pregnancies.
There exist various types of contraception methods. With proper use, chemical ones are highly efficient.
Contraception can take place on three levels:
- Preventing oocytes from meeting sperm cells
- Hindering ovulation
- Hindering fertilization or the implantation of the fertilized oocyte
Here we are interested in the methods that hinder implantation.
The "morning after pill"
With this method high dosages of estrogen combined with progesterone or a high dosage of pure progesterone is ingested as soon as possible after unprotected sexual intercourse or within 72 hours afterwards, at the latest. The efficiency of this approach amounts to around 99%, but it represents a hormonal overdose.
Various mechanisms appear to work together: namely an inhibition of ovulation, interference with the transport of the oocyte/sperm through the fallopian tube, interference with fertilization, and changes to the endometrium. Thereby this contraceptive method intervenes before the oocyte is implanted in the uterus.
Is a chemical substance that interrupts early pregnancy. The active substance is a synthetic steroid molecule, the strongly anti-progesterone-property of which is based on a competitive inhibition of the progesterone receptors. Mifepriston or RU486, which gives the pill its name, has an anti-nidation effect on the endometrium, the uterine muscle, and the cervix.
With this type of pregnancy interruption, the efficiency is increased to 95% by a combination with prostaglandins. The rejection of the embryo is also accelerated. Mifeprison must be ingested, though, within 49 days, at the latest, after menstrual bleeding has ceased.
The first examples come from 1920! Finely made plastic models with copper threads have been obtainable only since 1970, however, and the newer ones even release progesterone.
With an intra-uterine device (IUD) a double function is involved: firstly, implantation is hindered and, secondly, sperm cells are immobilized. This method for contraception exhibits an efficiency of around 90% and is widely employed.
A spiral IUD is made of plastic, contains copper threads, and is placed inside the uterine cavity. They can be inert or medicinal (slowly giving off small amounts of copper or progesterone).
Copper-containing IUD's immobilize the sperm cells in that copper inhibits the mitochondrial metabolism.
The progesterone that some IUD's release also thickens the cervical mucous plug (making access to the uterine cavity more difficult for the sperm cells) and alters the endometrial epithelial coating. Because of their mechanical irritation, all IUD's trigger an endometrial inflammatory reaction with leukocytosis and release of prostaglandin. These together affect the cervix, the uterus, and the fallopian tube, hindering a fertilization of the oocyte by a sperm cell.