How Often Does Emergency Contraception Work as an Abortifacient?

Updated to add: I’m working on a book on this subject. So far, I’ve determined that at least 1.3 million prenatals are killed by abortifacient emergency contraception worldwide each year.


Life begins at conception; therefore, the direct destruction of a conceived prenatal, any time after fertilization, as a result of a deliberate knowing choice of the human person, is a type of direct abortion.

Even if we define pregnancy as beginning at implantation, a human being’s life begins at fertilization, with unique DNA and with a process that continuously moves toward development and birth. After fertilization, during meiosis, the chromosomes obtained from the ovum and from the sperm undergo a process called “chromosomal crossover“, in which they swap segments of DNA. As a result, the 23 pairs of chromosomes of the conceived prenatal are each unique; they are not the same as any chromosome from mother or father.

Since each human person’s life begins at fertilization, the destruction of the prenatal after fertilization, but before implantation is a type of early abortion. Abortifacient is the term used to describe a chemical or device that is able to abort the conceived prenatal, especially when this abortion is not identifiable in the particular case. Abortifacient contraception sometimes works by preventing conception, and other times by destroying the conceived prenatal. Abortifacient contraception has both pre-fertilization and post-fertilization mechanisms of action, which is why abortifacient contraception is more effective than mere contraception (e.g. condoms).

Many medical sources have redefined “abortifacient” so that it only refers to the destruction of a prenatal after implantation. But at that point, the destruction of the prenatal is properly termed abortion, not abortifacient. So essentially, they have redefined “abortifacient” into oblivion. You can’t really have an abortifacient event because it either happens before implantation, and so they claim it is not the termination of a pregnancy, or it happens after implantation, and should be called abortion, not abortifacient.

Emergency Contraception (EC)

EC works by abortifacient mechanisms most of the time. A study of Levonorgestrel (LNG) emergency contraception (Stanford 2007) found that the chances that this type of EC would work as an abortifacient, rather than a contraceptive, increased as the time from intercourse to use of the EC increased [1], and as the effectiveness of the form of EC increased. The study authors developed a chart to estimate the percent of effectiveness that was due to post-fertilization (i.e. abortive) effects, based on those two variables, time from intercourse and effectiveness when taken at that time.

“The actual effectiveness of LNG EC has been estimated between 58% and 95% under different delays in administration [citation of 6 studies]. In some of the studies, a decrease of effectiveness with delay was noted, in others not.”

So different studies have stated different levels of effectiveness for LNG as an EC. Some studies found no decrease in effectiveness as the time from intercourse to use of the EC increased, and others found a decrease in effectiveness. At the median value of 76.5% effectiveness, the percent of effectiveness due to abortifacient mechanisms is about 18% for a 24 hour delay between intercourse and EC use; 60% for 72 hours delay; 72% for 96 hours. Most studies considered only cases where women waited zero to 5 days (120 hours). However, some studies did find use of EC beyond the 5 day mark, up to 10 days [2]. The average delay before using EC is likely in the 2 to 5 day range; at 3 days, the abortifacient action of the EC is above 50%.

For the absolute low of 58% effectiveness, a 72 hour delay offers 42% effectiveness from abortifacient activity, and a 96 hour delay (4 days) brings the number above 50%. For the high of 95% effectiveness, the EC is 10% abortifacient even if used immediately; 38% at 24 hours; 78% at 72 hours; 90% at 96 hours. Although the exact effectiveness with each delay is not known, the data available suggests that EC with LNG obtains most of its effectiveness from abortive action, not contraceptive action.

The same concept applies to IUDs used as EC, with one difference: it is indisputable that IUDs as EC are over 99% effective. A meta-analysis of past studies on EC (almost entirely from IUDs) included 6,834 EC events after intercourse [2]. The number of pregnancies was 6. The total failure rate of these IUDs as EC was 0.09% — not nine percent, but rather nine one-hundredths of one percent. The effectiveness, then, was 99.91%. Most of the time, the women received the IUD as EC 48 hours or more after intercourse (presumably because they had to schedule an appointment). And when used as EC, the IUD remains in place, in almost all cases, continuing to work as abortifacient contraception.

Conception may occur up to 5 days after intercourse. So if the EC is used beyond the 5 day mark, it can only possibly work by abortive action, not by preventing fertilization. In the above mentioned study, none of the pregnancies occurred when the IUD was inserted after day 5. Now in many cases, the woman would not have conceived from the single act of intercourse in question. But with a study size of over 6,800 EC events, many conceptions would have occurred.

For a single act of intercourse sometime during the week of ovulation, the odds of conception are 15% [3]. If you do not know the day of ovulation, then a single act of intercourse has about a 25% chance of occurring during the week of ovulation. Average cycle length is 28 days; 7/28 is 25%. So for a single act of intercourse without knowing the timing of ovulation, the odds of conception are about 3.75% (0.15 x 0.25). However, even for EC use, a woman is less likely to have intercourse during menstruation (the first several days of her cycle) [4]. So the chances of conception increase somewhat. At 4 to 5% chance of conception and 6,834 EC events, 273 to 342 conceptions would have occurred, and yet there were only 6 resultant pregnancies [2]. What percentage of this effectiveness was from abortifacient action? Over 80%, and possibly over 90%, based on the Mikolajczyk and Stanford study (Joseph B. Stanford, the physician, not the educational institution).

Another type of chemical EC is called UPA (Ulipristal Acetate) also known as “ella” or “ellaOne” (r), the brand name. This type of EC is likewise nearly 100% effective, no matter how long after intercourse the EC is used. And that fact implies, again, that abortifacient effects are a major component of its effectiveness.

If the sole mechanism of action were preventing conception, then the effectiveness of the EC should diminish as the time between intercourse and use of the EC increases. Then, by the 5 day mark, the EC should be completely ineffective, if it is only a contraceptive. And yet this is not the case for any type of Emergency Contraception. They are all effective even 5 days or more later, indicating that they have major abortifacient mechanisms of action.

Yet many medical authorities adamantly claim that EC is not abortifacient. They can say that only because they have redefined abortifacient to refer only to the destruction of the prenatal after implantation. They know that these methods of EC work between fertilization (conception) and implantation. They just don’t want their patients and the general public to know it.

Ronald L. Conte Jr.
Roman Catholic theologian and translator of the Catholic Public Domain Version of the Bible.

Please take a look at this list of my books and booklets, and see if any topic interests you.

[1] Mikolajczyk and Stanford, “Levonorgestrel emergency contraception: a joint analysis of effectiveness and mechanism of action”, Fertility and Sterility, September 2007, Volume 88, Issue 3, Pages 565–571.
[2] Kelly Cleland, et al., “The efficacy of intrauterine devices for emergency contraception: a systematic review of 35 years of experience”, Human Reproduction, Volume 27, Issue 7, 1 July 2012, Pages 1994–2000;
[3] Allen J. Wilcox, et al., “Timing of Sexual Intercourse in Relation to Ovulation — Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby”, December 7, 1995; N Engl J Med 1995; 333:1517-1521.
[4] Paul Fine, et al., “Ulipristal Acetate Taken 48–120 Hours After Intercourse for Emergency Contraception”, Obstetrics & Gynecology, Vol. 115, No. 2, Part 1, February 2010; Fig. 2. Distribution of unprotected intercourse across reported cycle days.

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