I investigated all different types of chemical birth control (The Pill, mini-pill, the shot, Nuvaring, all types of IUDs) and what I found SHOCKED me. All of them can cause a fertilized egg to be aborted. One effect of all of them is to thin the endometrium which is the lining of the uterus. This means if an egg is realeased and does get fertilized, it is unlikely to implant in the uterus. (You can read the Full Prescibing Information provided by your pharmacist or found on-line to confirm this.) Since it isn't implanted, it dies from lack of nutrition and is washed away in the next cycle. The mother never notices, since the lighter period is what caused the baby to die.
Since I believe a fertilized egg is a baby, this was unacceptable for me. Even the chance of one of my babies starving to death was too great a risk for me.
I know not everyone will agree with me, but I wanted to put the information out there for those who might agree with me but did not know about the abortifacient properties of chemcial birth control.