How DO contraceptives work?

Here is an extremely controversial question: How DO modern contraceptives work?  A closely related question: Do any of the modern hormonal contraceptives and IUDs work by causing an abortion?

A woman is said to be pregnant when the early embryo has successfully made its way through the lining of the uterus establishing contact with the maternal circulation.  This process is called implantation.

Here is an easily understood example.  A couple with infertility problems is trying to become pregnant via in vitro fertilization (IVF). Several eggs are harvested from her ovary, transferred onto a carefully prepared medium and then the man’s sperm are flooded over the woman’s eggs.  They get together in that dish and their development is followed using a microscope. 

Soon thereafter several fertilized eggs are transferred into the woman’s uterus. Shortly after that a test is done.  If implantation has not occurred the pregnancy test is negative.  Up to this point, has fertilization happened? YES, IT HAS?  Has implantation happened? NO, IT HAS NOT. And is she yet pregnant? NO, SHE IS NOT. To review: if implantation has NOT happened her pregnancy test is negative and the couple, so eager to be told “You are pregnant” is told “You are not pregnant yet.  Implantation has not happened.”

In other words, no implantation – no pregnancy. Several days later if implantation has happened her pregnancy test will become positive and THEN the couple will be told “You are pregnant!”

All of the hormonal contraceptives, combined birth control pills, progestin-only pills, contraceptive rings, contraceptive patches, Depo-Provera injections, the hormonal IUD called Mirena, and the Implanon implant  work primarily by stopping ovulation (no egg, then no pregnancy) OR by preventing the ascent of sperm up to the egg (no fertilization – no pregnancy). The copper IUD called ParaGard also works primarily by stopping fertilization but perhaps 3 % of the time works by blocking implantation. Every single one of these methods can alter the lining of the uterus (the endometrium) preventing implantation (no implantation – no pregnancy). And perhaps most important, none of these methods will interrupt the process after implantation (NO INTERRUPTION OF AN IMPLANTED BLASTOCYST, NO ABORTION)

It would appear that whether women will continue to be able to choose to use the very best of our modern contraceptives, the three Long Acting Reversible Contraceptives (LARC methods) and all the other hormonal contraceptives is going to depend in large part on the way PREGNANCY and PERSONHOOD are defined. If a woman is deemed to be pregnant as soon as fertilization occurs, then anything that stops the reproductive process after fertilization is defined as an abortion. This would mean that all the modern contraceptives developed since 1960 (and used by well over 90 percent of American women) would be unavailable for many women. Then these women would not be able to choose consciously whether they will or will not become pregnant.

Robert A. Hatcher MD, MPH
Professor of Gynecology and Obstetrics
Emory University School of Medicine
Atlanta, Georgia