Zygotes Lost With Birth Control v. Without Birth Control

A few weeks ago I came upon a blog post by Sarah of Who I Am Without You comparing the number of fertilized eggs, or zygotes, that fail to implant and are flushed out of a woman’s body when she is on the pill with the number of fertilized eggs that naturally fail to implant and are flushed out when a woman is not on the pill. I found her analysis fascinating and worth further investigation.

Let me preface this with a quick biology lesson. Every month, a woman’s body releases an egg. If there is sperm there waiting, the egg becomes fertilized. This is when I was taught life – including personhood and the bestowing of a soul – began. This fertilized egg, or zygote, then travels into the uterus, where it implants in the uterine wall. That is when pregnancy begins. The birth control pill works primarily by preventing ovulation in the first place, and also by impeding sperm so that it can’t get to to an egg to fertilize it. But leading organizations in the pro-life movement argue that there is some chance that women on the pill will have “breakthrough ovulation,” and if this occurs and sperm somehow make their way to the egg, you could technically end up with a fertilized egg. They further suggest that because the pill also thins the uterine lining, this fertilized egg would be flushed out of a woman’s body rather than implanting in her uterus.

The pro-life movement is divided between Catholics and Protestants. Catholics oppose birth control for religious reasons, but the Protestants in the movement who take issue with birth control generally do so because, based on the information detailed above, they believe that it is an “abortifacient.” In other words, they believe that the pill causes abortions.

So, with that background, Sarah’s numbers were as follows:

Without Birth Control:

  • Out of 100 fertile women without birth control, 100 of them will ovulate in any given month.
  • Out of those 100 released eggs, 33 will become fertilized.
  • Out of those 33, 18% will be rejected by the uterus.
  • In a group of 100 women not on birth control: 6 zygotes will “die”

With Birth Control:

  • Out of 100 fertile women on birth control, around 6 of them will ovulate in any given month.
  • Out of those 6 released eggs, only 2 will become fertilized.
  • Out of those 2, 100% will be rejected by the uterus.
  • In a group of 100 women on birth control: 2 zygotes will “die”

I should point out that  an increasing pile of evidence suggests that the pill does not actually result in fertilized eggs failing to implant and being flushed out of a woman’s body. What I think is important about Sarah’s analysis, though, is that she uses the pro-life movement’s own numbers, numbers it uses to justify its opposition to the pill as a supposed “abortifacient.” In other words, Sarah plays the game by the pro-life movement’s rules, and finds that birth control would actually, by their own arguments, save the lives of fertilized eggs, or zygotes.  I wondered about the numbers Sarah used, so I went looking for verification. I used numbers from pro-life websites as I did so. What I found is as follows.

An article from the Life Issues Institute states that when a woman is on the pill an egg is released, fertilized, and flushed out only 1 or 2% of the time. This initially seems to correspond well with Sarah’s estimate of 2 zygote deaths per 100 women on the pill. However, I did some additional digging and found an article on Pharmacists for Life that explained that there are as many as 17 ovulations per 100 women on the pill in a year. This means that Sarah’s estimate of six eggs released per 100 women on the pill per month is actually four times too high, and that there are actually only 1.5 eggs released per 100 women on the pill each month, not six as Sarah estimates.

Now, the Life Issues Institute article based its estimate on the the assumption that breakthrough ovulation occurs 20% of the time. Comparing this number with the number from Pharmacists for Life – 17 ovulations per 100 women on the pill per year – indicates that the 20% breakthrough ovulation statistic refers to the number of women who experience breakthrough ovulation annually, not monthly. This is important because the first site makes it sound like a given woman on the pill will ovulate 20% of the time, and that’s quite simply not the case. Rather, of all women on the pill, 20% of them will ovulate once in a given year. Or rather, if you take the number actually attributed to a scientific study, 17%.

And more than that, the Life Issues Institute article stated that because of the pill’s effect in impeding sperm, eggs released through breakthrough ovulation will be fertilized only “two or three times out of the twenty.” In other words, Sarah’s estimation that 30% of these eggs will be fertilized is too high, and the actual number that will be fertilized is more like 10 to 15%. If only 1.5 eggs per 100 women are released per month, and only 10% of those are fertilized, that means there are only 0.15 fertilized eggs flushed out per 100 woman per month.

There is something else to consider here as well. Something like 25% of pregnancies end in abortion. Without birth control, 85 out of 100 women will end up pregnant in a given year. So, if the 100 women currently using birth control go without for a year, 85 will become pregnant and 21 will have abortions. Probably more than 21 actually, since the fact that those 100 women would have otherwise been on birth control means that all 85 of those pregnancies would be unplanned. Since the roughly 25% abortion rate is for all pregnancies, and we can assume that nearly all of those abortions are performed on the 40% of pregnancies that are unplanned, the abortion rate for unplanned pregnancies is probably closer to 62.5%. Thus 53 of those 85 pregnancies would probably end in abortion, meaning 53 “unborn babies killed.” This in contrast to the 2 zygotes flushed out each year (0.15 times 12 months) per 100 women on birth control. In other words, even if the pill is an “abortifacient,” making it widespread and available has the potential to decrease abortion so much so that it ought to be a moral imperative for those who really are in it to “save unborn babies.”

We’ve looked at the “with birth control” numbers to see how they check out, and now it’s time to turn to the “without birth control” numbers. When I looked for confirmation for Sarah’s figure that 18% of all fertilized eggs are naturally rejected by a woman’s body what I actually found was that that figure is too low.

As a natural protective mechanism, the uterus tends to reject fertilized eggs that take too long to adhere to the lining because they may be less fit, the researchers say. On day 11, more than 50 percent of pregnancies fail and on day 12, that number jumps to over 80 percent. (Source)

Studies have found that 30 to 50 percent of fertilized eggs are lost before or during the process of implantation – often so early that a woman goes on to get her period at about the expected time. (Source)

In nature, 50 percent of all fertilized eggs are lost before a woman’s missed menses. (Source)

Correcting Sarah’s figure to 50% means that in a given menstrual cycle 16 zygotes, rather than 6 zygotes, will “die” for every 100 women not on the pill. So let me quote Sarah’s comparison again, but with the numbers corrected.

Without Birth Control:

  • Out of 100 fertile women without birth control, 100 of them will ovulate in any given month.
  • Out of those 100 released eggs, 33 will become fertilized.
  • Out of those 33, 50% will be rejected by the uterus.
  • In a group of 100 women not on birth control: 16 zygotes will “die”

With Birth Control:

  • Out of 100 fertile women on birth control, around 1.5 of them will ovulate in any given month.
  • Out of those 1.5 released eggs, only 10 to 15% will become fertilized.
  • Out of those 0.15, 100% will be rejected by the uterus.
  • In a group of 100 women on birth control: 0.15 zygotes will “die”

Now of course, if you have 100 women not on birth control, some of them will get pregnant, so they won’t all ovulate in every given month. This means that the comparison above is a bit unfair. On first glance, it sounds like this would level the playing field and make the difference between zygotes flushed out for those not on the pill and zygotes flushed out for those on the pill insignificant. However, this is not the case.

Eighty-five percent of women will become pregnant in a given year. I am not sure where Sarah got her estimation that 33 women per month would have their eggs fertilized, but it checks out. Why? Because if half of those 33 eggs are fertilized, as the stats I quote above indicate that they would be, that’s 16 women becoming pregnant per month. If you run that percentage out – if 16% of your sample becomes pregnant per month – you end up with a total of roughly 85% of the women in your sample becoming pregnant in a given year, which is right on target. But if 16% of your sample becomes successfully pregnant each month, another 16% have fertilized eggs that are flushed out of their bodies naturally, spontaneous abortions resulting in dead zygotes. The math is getting complicated here, but I ran the numbers through – 16% out of 100 the first month, 16% out of 84 the next month, etc. – and for 100 women over the course of one year you will end up with around 85 dead zygotes even when you account for the fact that almost all of the women in the sample will end up pregnant by the end of the year.

With Birth Control:

  • Sample size: 100 fertile women
  • 0.15 dead zygotes per month
  • 2 dead zygotes by the end of the year

Without Birth Control:

  • Sample size: 100 fertile women
  • Each month 16% become pregnant and 16% have dead zygotes
  • 85 dead zygotes by the end of the year

Just in case starting the sample with 100 women who are not pregnant somehow skewed the numbers, let’s simply consider two individual women over their lifetimes. Let’s say that each has 25 fertile years. One is on the pill the entire time. If we add up her 2% chance per year of having a zygote flushed out, we end up with a 50% chance over her lifetime. The other woman does not use birth control. For every menstrual cycle, there is a 16% chance that she will have a zygote flushed out. This means that out of six periods, on average she will have one zygote flushed out – one fertilized egg that will fail to implant in her uterus. While without birth control she will likely spend much of her time pregnant, she will still have periods in between pregnancies. And since it’s just as likely that a zygote will fail to implant in between two pregnancies as it is that it will successfully implant, thus starting another pregnancy, she will probably end up with just as many dead zygotes as she ends up with pregnancies.

Thus a woman on the pill for her entire fertile period has a one in two chance of her body “killing” a zygote by flushing it out, but the body of a woman not on birth control will flush out and thus “kill” numerous zygotes over the course of her life. Sarah’s numbers, then, are low. The actual numbers indicate that a woman on the pill for her entire life flushes out something like 95% fewer zygotes than a woman not using birth control.

The implication of all of this, of course, is not lost on Sarah:

So let’s get this straight, taking birth control makes a woman’s body LESS likely to dispel fertilized eggs. If you believe that life begins at conception, shouldn’t it be your moral duty to reduce the number of zygote “abortions?” If you believe that a zygote is a human, you actually kill more babies by refusing to take birth control.

How has such a massive flaw gone unnoticed all this time? Did anti-birth control advocates really just “miss” these obvious facts, or could it be that they like the result of this misconception? Denying women rights to their own reproduction is the oldest weapon in the war on women. Even if you believe that a zygote deserves the same rights as a full grown human, there is still no reason to oppose birth control other than to control women.

I don’t know about you, but I’ve had enough of the “personhood” smokescreen. Let’s call the anti-birth control message by its real name: anti-woman.

The Biased . . . and the Confused
Sad but True
The Totally Unoriginal Atheist Case against Abortion
When Abortion Restrictions Mean Jail Time
About Libby Anne

Libby Anne grew up in a large evangelical homeschool family highly involved in the Christian Right. College turned her world upside down, and she is today an atheist, a feminist, and a progressive. She blogs about leaving religion, her experience with the Christian Patriarchy and Quiverfull movements, the detrimental effects of the "purity culture," the contradictions of conservative politics, and the importance of feminism.

  • smrnda

    Great post. I’ve never been on the pro-forced-pregnancy side, but a course in embryology made me completely reject the notion that the use of contraception was equivalent to abortion in any way.

  • http://politicsproseotherthings.blogspot.com/ Nathaniel

    And the response from the Catholic bloggers on this site will be crickets.

  • http://kagerato.net kagerato

    I suspect the fundamentalist response will be that math is a tool the devil uses to deceive you. Sadly, I’m not being entirely facetious.

  • Shayna

    I tried to leave this as a comment on Sarah’s original post, but I didn’t have an account that would work for her blog. All of these statistics are based on the assumption that hormonal BC (the Pill and emergency contraception in particular) causes failed implantations. Historically, this warning has been included on BC because scientists thought it was possible that the Pill could act that way.

    Current research, however, indicates that emergency contraception does NOT act that way, and never did. If EC doesn’t, it is highly unlikely that the regular Pill does either. See this New York Times article , for example: http://www.nytimes.com/2012/06/06/health/research/morning-after-pills-dont-block-implantation-science-suggests.html?pagewanted=all

    • Tess

      What Shayna said. I ran through the same sorts of calculations you did, Libby, about 6 months ago, which of course I found convincing enough in their own right, but I also point you to this source:
      It’s from a pro-life group, but it’s one of the most extensive collections of the literature existing on hormonal contraception that I’ve found, (after all, the pill’s been around awhile, so there have been numerous studies by now), and it all seems to suggest that there is little evidence that the Pill/other combined hormonal methods cause an increase in failed implantations (once well-documented spermicidal effects are taken into account).

      • Tess

        And I see you actually already addressed that in your article. :P Whoops, nevermind! Fun analysis.

        Just because I can, I’ll note that the percent chance over a lifetime of having one or more zygotes flushed out for a woman on hormonal contraception is actually less than 50%. Adding the 2% each year makes a decent estimate, but the actual probability should be (1-.98^25)*100%, or ~39.7%, certainly not harming the argument.

  • Christine

    It’s a deontological ethical system taken too far. It is the actions you take – you must do the right thing – that matter, not the overall outcome. (Let’s not be too hard on the deontological systems – teleological ethical systems are just as bad when taken to extremes). What really boggles my mind is that in choosing between two ‘wrongs’ – harassing people and allowing abortion to continue, the passive one is considered a larger wrong EVEN THOUGH it doesn’t have a good outcome.

  • Noelle

    None of this is new information, but it’s always good to see people understanding science.

  • Felicia

    Are these numbers similar with IUDs? I got in a discussion with some prolife friends the other day who were fine with birth control pills because they found research basically stating the same as your post but were against IUDs because they said they were more likely to cause a zygote to implant than what naturally occurs. I would think that the numbers would not be more than what happens naturally according to the same logic you discuss in this post but I have had difficulty finding information on it.

    • Knittinggoddess

      I don’t know the numbers with IUDs, but here is a livejournal community post with LOTS of studies and explanations of how they work: http://iud-divas.livejournal.com/2894716.html

      Story short: IUDs, even copper ones, don’t inhibit implantation. The copper ions immobilize and kill sperm and ova. The body also puts out an inflammatory immune response in reaction to the IUD, which also kills sperm and ova. Hormonal IUDs have that same inflammatory response, and also the progesterone makes a thick cervical plug that traps all the sperm like a fly trap.

      I saw a study from the early 80s–I can’t find it now, but it was on the website of Planned Parenthood International or WHO–that specifically flushed out the uterus contents of people with and without IUDs, and found fewer unimplanted zygotes in the IUD group than in the no-IUD group. There is no evidence that IUDs prevent implantation.

  • http://www.thichchup.com/link/20 Penney

    After looking into a handful of the blog articles on your website, I really appreciate your technique of writing
    a blog. I added it to my bookmark webpage list and will be checking back
    soon. Please visit my web site too and tell me what you think.

  • Jamie

    Good stuff, though I would phrase one aspect differently. Rather than saying that “Sarah….finds that birth control would actually, by their own arguments, save the lives of fertilized eggs, or zygotes.” shouldn’t it just be said that birth control results in “fewer dead fertilized zygotes”. The birth control pill doesn’t SAVE zygotes, it just results in fewer zygotes to end up dead. (“Dead” of course, being an arguable term anyway since zygotes don’t meet the biological definition of “life” yet….but I guess we can refer to them as “dead” in the same way we refer to “dead tissue” or something.)

  • http://spaceysteph.blogspot.com SpaceySteph

    Wow. After reading this I have decided: God doesn’t think life begins at conception either.

  • http://thedeadauthorsclub.wordpress.com Christine

    Your analysis would be relevant if the goal of the politically powerful pro-life movement was actually to avoid dead zygotes. The goal of the pro-life movement, if you drill down a little bit further, is always and completely to respond to sexually active women by mandating that they to carry any pregnancies that result from that sexual activity to term without allowing them a means of avoiding conception other than abstinence. This can be seen over and over in the way that the politically powerful respond to issues like birth control and abortion. They continually talk about pregnancy as the “price” of sex. And that “choice” is to be made by abstaining. This of course, completely ignores the fact that a lot of women who are sexually active are actually married and involved in governmentally sanctioned sexual activity.

    Sandra Fluke, in their eyes and in the media meme that was created, was a slut who demanded to be paid for having sex because she testified before Congress about the rules allowing an employer conscience objection to a requirement that insurance companies cover contraception. But, honestly, it would’ve been better to have a married woman testify before Congress. Because the pro-life movement wants to pretend that it is only sexually-active unmarried woman who are worried about abortion and birth control. Nothing could be further from the truth. Telling a married couple to abstain from sex, or requiring that they following some religiously approved “natural” contraception method – regardless of the fact that they don’t share that religious tradition – simply obscures reality. And the reality is this: much of the pro-life power structure is actually pro-pregnancy. They are pro-getting-wimmin-pregnant-and-keepin’-em-pregnant no matter what. And no matter what they, their husbands, and their other children think is the optimum family size for their family.

    This may not be what the rank and file believes. But I have seen too many quotes from Rick Santorum, and Foster Friess, and Todd Akin, and Franklin Graham, and other people who have the power to impose their political will on the rest of us, to be fooled. And the fact that they are capable of fooling their supporters doesn’t mean that they are fooling the rest of us.

    • http://www.facebook.com/people/Dave-Carroll/100003342890124 Dave

      You’re conflating wanting to control women’s sexuality with simply not wanting to be forced to subsidize other’s sex lives. The latter is what Sandra Fluke selfishly demanded. I don’t care what she does in her private life but let her pay for it herself. Or if an employer wants to voluntarily provide birth control coverage to employees as an incentive for people to work for him/her fine, but let it be voluntary. She nor anyone else has a right to force anyone to provide birth control to someone just because they happen to own a business. If you’re really an independent woman then you should be able to take care of yourself, the fact that left wing feminists are unwilling to throws the whole narrative into question. Especially since birth control isn’t even that expensive.

      • Alix

        So, if the point is not to subsidize other people’s sex lives, why do insurance companies cover viagra?

        Also, birth control can be expensive, depending on the kind. Also also, it’s used for more than just birth control.

        But more to the point, a hell of a lot of elective things are covered by insurance, and no one cares. Again: viagra.

        I fail to understand why it’s selfish for a woman to want her birth control covered, but it’s not selfish for men to want to keep having erections long after their dick’s petered out on them. Why do men get more freedoms with less condemnation than women?

        Oh, right, because sexist assholes, that’s why.

        (Also: what on earth is up with folks commenting on very dead threads?)

  • Darren

    Over at Dr. Jen Gunter’s blog, there is a discussion of the Savita Halappanavar case. One of the commenters discussed how many fertilized ova fail to result in live births and he included multiple citations. I though I would pass this along to your blog; its always nice to have sources.

    ”I’m not a physician, just a lay IT guy with in interest in the issues. I was interested in the question, “how many fertalized ova (“Innocent human babies” in pro-life terms) naturally fail to result in live babies.” What I found was horriffically shocking and rarely seems mentioned.
    Aproximately 70-78% of fertalized ova never become live babies. Roughly 31% fail to implant in the uterus, another 30% spontaneously self-destruct before the woman even knows she’s pregnant (post-implantation but pre-clinical). The remaining 12-14% spontaneously abort, most commonly due to genetic or developmental defects.
    Facts from the studies:
    * 5-20% of human sperm and eggs carry significant genetic defects.
    * ~95% of first trimester pregnancy loss is due to genetic abnormalities.
    * There are peaks in the miscarriage rate in the 12th and 20th week, with the rate of miscarriage dropping below 1% after the 26th week.
    * Even at 20 weeks, 5-13% of pregnancy failures are attributible to genetic defects.
    Pregnency and miscarriage doesn’t show use the ‘hands of a loving god’; but rather an enormously complex bio-mechanical process, which often ends up breaking down. Spontaneous abortion and miscarriage, especially early on, is most often natural quality control. It’s a good thing.
    This is not to belittle the pain women feel at the loss of a child, nor the preciousness of newborn life. It is hard for us, however to face the naked facts of a process when our feelings are involved.
    Article: Human pre-implantation embryo development
    Authors: Kathy K. Niakan1,2, Jinnuo Han3, Roger A. Pedersen2,4, Carlos Simon5 and Renee A. Reijo Pera
    Ref: doi: 10.1242/dev.060426 March 1, 2012 Development 139, 829-841
    Date: March 1, 2012
    Source: http://dev.biologists.org/content/139/5/829.full
    Article: Conception to ongoing pregnancy: the ‘black box’ of early pregnancy loss
    Authors: N.S.Macklon, J.P.M.Geraedts and B.C.J.M.Fauser
    Date: 2002
    Source: http://humupd.oxfordjournals.org/content/8/4/333.full.pdf
    Article: Genetic and Nongenetic Causes of Pregnancy Loss
    Authors: Simpson, J, Carson, S, Glob. libr. women’s med.,(ISSN: 1756-2228) 2011; DOI 10.3843/GLOWM.10319
    Date: Updated Dec 2011
    Source: http://www.glowm.com/index.html?p=glowm.cml/section_view&articleid=318

    • Niemand

      Spontaneous abortion and miscarriage, especially early on, is most often natural quality control. It’s a good thing.

      Is it? People in the “pro-life” movement profess to be horrified at the high rate of abortion for trisomies. If it is immoral to abort a fetus with down syndrome or one of the worse trisomies, why is it not also a horrific thing that many of them abort spontaneously? If it is a good thing that many of them abort spontaneously, why is it bad that women choose to abort others?

      • Darren

        ”If it is immoral to abort a fetus with down syndrome or one of the worse trisomies, why is it not also a horrific thing that many of them abort spontaneously?”

        A very good question. Libby touches on this issue in her post, How I Lost Faith in the “Pro-Life” Movement, when she asks, “Why No 5K to Save the Zygotes?”

  • Ken
  • violetdoll

    Thank you! This is always my exact point when this comes up. BCP equals less “dead babies” so they should be giving them out with the freaking Eucharist at mass if they really cared about the lives of the unborn.

  • HelenBrame

    The 0.15 zygotes in 12 months adds up to 1 baby a year. That is one baby murdered. Sixteen zygotes a year times 12 equals one hundred ninety two babies that God chose to not let live. He preordained for them to be in Heaven. There is no tragedy there, sorry. Not if you believe.

    I would also add that most people who are not on the pill and not seeking pregnancies are avoiding the day of ovulation and therefore, many Catholics actually practicing and living Catholic dogma would not be “killing” their zygotes— by any means.

    • Anne

      “There is no “one baby murdered”. Whether a zygote implants in the uterus or is flushed out of a woman’s body it happens without her even being aware of its existence- regardless of what type of birth control she’s using and regardless of whether or not she wants to be pregnant.
      Do flushed-out zygotes have souls that go to heaven? I can’t say for sure and neither can anyone else. But either God chooses for ALL those babies to go straight to heaven, including the ones whose mothers are on the pill, or it’s something that just happens sometimes as a normal part of life. Neither are “killing their zygotes.”