"Development of the embryo begins at Stage 1 when a sperm fertilizes an oocyte and together they form a zygote."
[England, Marjorie A. Life Before Birth. 2nd ed. England: Mosby-Wolfe, 1996, p.31]
So if you can get pregnant with it in, obviously you can get pregnant and kill your baby before you even realize you are pregnant. And it is NOT controlling pregnancy, but like its name birth!
"Fertilization is a sequence of events that begins with the contact of a sperm (spermatozoon) with a secondary oocyte (ovum) and ends with the fusion of their pronuclei (the haploid nuclei of the sperm and ovum) and the mingling of their chromosomes to form a new cell. This fertilized ovum, known as a zygote, is a large diploid cell that is the beginning, or primordium, of a human being."
[Moore, Keith L. Essentials of Human Embryology. Toronto: B.C. Decker Inc, 1988, p.2]
A Mirena slowly releases very small amounts of the hormone levonorgestrel directly into your uterus.
There is no single explanation for how Mirena works. Mirena may:
- Thicken cervical mucus to prevent sperm from entering your uterus
- Inhibit sperm from reaching or fertilizing your egg
- Make the lining of your uterus thin
Mirena may stop the release of your egg from your ovary, but this is not the way it works in most cases. Most likely the above actions work together to prevent pregnancy. Like other forms of birth control, Mirena is not 100% effective. If there is a chance that you could become pregnant than there is a chance that you could abort!