How the Pill Works
According to Web MD, hormonal birth control (including the pill, the mini pill, Depo-Provera, the patch (Ortho Evra), and vaginal rings) work in several ways. They inhibits sperm traveling through the cervix by thickening the cervical mucus, and they prevent a woman from releasing eggs from her ovary. (At least, some of the time. More on that in a moment.) Hormonal birth control also makes the lining of the womb "inhospitable."
How the Pill Can Cause an Abortion
The website for Association of Prolife Physicians states that "there is an impressive amount of medical literature" backing up the last mentioned way the pill is known to work - by preventing eggs from implanting in a woman's uterus. The hormones in the pill do this by making the endometrium thinner. Through in-vitro studies, most doctors believe a thin uterus makes it difficult to become pregnant. But if the pill works in this fashion, that means an egg has already been fertilized and the act of preventing it from implanting means the pill isn't actually working as a contraceptive. Instead, it is causing an abortion.
Fertilized Eggs on the Pill?
Most of us were taught the pill works by preventing ovulation. Yet the pill is not 100% effective in this area. Even when you consider the best possible statistics physicians offer - that, as Planned Parenthood reports, 1 out of 100 women who take the pill perfectly get pregnant anyway - it's clear the pill does not always prevent ovulation or fertilization. (Other sites offer a lower effectiveness rate; for example, Feminist Women's Health Center says the pill is 92 to 99.7% effective. Mini pills are even less effective than traditional birth control pills, preventing pregnancy about 95% of the time.) So while hormonal birth control won't always cause an abortion, they sometimes will prevent a fertilized egg from implanting in the womb, causing an abortion.
Abortion - or Not?
So why don't doctors warn their patients about this? It comes down to definitions. The American College of Obstetricians and Gynecologists insists a woman isn't pregnant unless the fertilized embryo implants in the womb. So does the National Institutes of Health. Implantation, however, doesn't happen until about three to four days after conception, according to Planned Parenthood.
As the Association of Prolife Physicians website states (emphasis added):
"One of my patients informed me recently that her gynecologist insisted that the morning-after pill prevents pregnancy 100% of the time and does not cause abortions. This may be true given the gynecologist’s definition of 'pregnancy,' but she is dead wrong in...implying from that this is when her baby’s life begins. Though designating this stage as the point at which pregnancy commences and life begins is convenient, it is arbitrary, palpably erroneous, and deceptive. Implantation into your mother’s uterus did not make you any more alive or human than did your first breath of air, your first meal, your first bowel movement, or any other arbitrary event in your life....More Info
[When I was at college] I publicly challenged [a professor's view of the morning-after pill] and he reluctantly admitted that the morning-after pill worked by preventing implantation of an already-conceived embryo, but he resolved the dilemma with the statement, 'I don’t consider it much of anything at that stage.' It came down to his unsupported bias against the humanity of small human beings!"
In addition to all the other links in this post, you can read a referenced article by a physician at Eternal Perspective Ministries. Two more references worth reading are Prolife OBGYNs' article "Birth Control Pill: Abortifacient and Contraceptive" and "Hormone Contraceptives Controversies and Clarifications." The latter argues there isn't enough proof hormonal birth control causes an inhospitable environment for fertilized eggs. You can also use the Prolife OBGYN's website to find a prolife doctor in your area.
Do Other Birth Control Methods Cause Abortions?
This post may lead some of you to wonder what other "contraceptives" might cause abortions. Me, too. After some research, it seems the IUD may also cause abortions. Despite the fact that Planned Parenthood's website states,
"Both the ParaGard and the Mirena IUDs affect the way sperm move, preventing them from joining with an egg. If sperm cannot join with an egg, pregnancy cannot happen. Both types also alter the lining of the uterus. Some people say that this keeps a fertilized egg from attaching to the lining of the uterus. But there is no proof that this actually happens."Studies do indicate that thinning ("altering") the uterus may prevent implantation, as referenced above. All the other websites I researched acknowledge this. For example, the Central Michigan District Health Department website states, "As with birth control pills, there is no single explanation for how IUDs work. Studies have shown that the presence of an IUD interferes with the movement of sperm, fertilization of eggs, and implantation." So if sperm does manage to fertilize an egg, the IUD's thinning of the uterus will cause an abortion.
What birth control methods definitely never cause abortions? ,Condoms, diaphragms, spermicide, cervical caps - and of course abstinence.