I’m convinced that Plan B does not block implantation. Because I keep getting emails, hearing radio personalities and reading posts on various forums claiming that Plan B is an abortifacient, here’s a review of information on the medical effects of the pills and on the other effects and lack of effects.
The overwhelming evidence – from several different groups of researchers – is that Plan B, the single ingredient protocol containing a synthetic progesterone called levonorgestrel, only works – when it works – the 5 days or so before and just after ovulation. Furthermore, since few women really know when they ovulate, and only slightly more women will even use the protocol when they have the pills in their medicine cabinet, easy access doesn’t change anything.
The best and most ethical research evidence, “On the Mechanisms of short term levonorgestrel administration as emergency contraception” is available online free of charge at this site.
If, as I believe, the pills only work in preventing fertilization, they are only medically justified/necessary 5 days before or one or 2 days just after ovulation, the window of fertility. The other 20 days or so of the menstrual cycle, the pills are useless and un-necessary.
The best evidence is that Plan B works to prevent ovulation or to prevent the oocyte (the “egg”) from being released from the ovary and passing to the fallopian tube. This is why the pill is best (and only?) functional before ovulation. In nature, the egg only lives about 24 hours and sperm can live from 2 to 5 days. If the egg is not released, is over 24 hours old, if the sperm cannot get to the egg or if they are dead or incapacitated, there can be no fertilization.
The only post-ovulation effect that has been proven that could prevent pregnancy also prevents fertilization. Levonorgestrel causes the mucus in the cervix to be thick (so sperm have a hard time getting to the uterus and then the fallopian tube where the egg is) and by making the sperm unable to penetrate the zona pellucida, the covering and nurturing cells around the oocyte or egg.
Biopsies of the uterus of women who have ovulated in spite of taking Plan B do not show any changes that would prevent implantation of the embryo. The blood flow and lining of the uterus is normal. Support for this lack of abortifacient effect in the uterine lining is the natural increase of progesterone in women after ovulation and the treatment of some infertile women with progesterone around ovulation or around transfer of the embryo in an in vitro fertilization cycle. Levonorgestrel and the other forms of progesterone actually seem to encourage implantation.
The reason I am still wary is the evidence that the “luteal” phase of the cycle – the time from ovulation to the time the woman starts shedding her uterine lining – is shortened in some women. If the lining is shed early, I can’t be sure that there could not be a loss of an embryo which is beginning to implant. (late note, October 3, 2007 – the evidence indicates that if the pill is taken before ovulation, the luteal phase is shorter, but the closer to ovulation -and the greater the chance of ovulation – the less effect on the luteal phase. So that I don’t worry, any more, about losing an embryo that way.)
Women continue to get pregnant – and have abortions – at about the same rates in England and other countries where Emergency Contraception is available without prescription. Part of the reason is that even when women have the medicine in their homes and have received education, they take the pills only about 20% of the time when they have unprotected sex. This month’s Contraception reports that only 11% of 706 women (ages 18 to 44 years old, who knew they were part of a study and who were at risk because they did not want to be pregnant but were using other contraceptives incorrectly) used the pills, even though the medicine is available without a prescription in that country.(H. Goulard et al./Contraception 74(2006)208-213)
And while studies have shown that women and girls don’t increase risky behavior, the same studies show that there is no decrease in such behavior, either.
I do wonder whether over the counter use in the US will lead to at least a short-term burst of promiscuity and abuse of women and girls, since the studies on access have all included only women and girls who went to clinics and at least received some education (and, as I said, even those women and girls didn’t change their risks).
The medicine has never before been available to men in the US. At least there has been some effort to provide education to women and girls receiving the medicine in Washington, where pharmacists could dispense the meds under certain conditions.
Anecdotal information from pharmacists and doctors in the UK, Jamaica and the Far East indicates that men buy EC at least as often as women and that that it appears that some women and girls are using EC more than once a month.
Here’s some links in this blog and other pro-life writers who have come to the same conclusion.
Progesterone, infertility and early pregnancy
Plan B Doesn’t Change Much (Actual article reproduced – New information on the study that is often quoted to prove that promiscuity doesn’t increase – in fact, there’s no change at all – But that’s even after going to the clinic, etc.)
A non physician who does a lot of research, “Ales Rarus”
Mangling, Mishandling, and Misrepresentation of Science in the Plan B Debate (Part II)
Another unquestionably pro-life blog, “Jivin’Jehosaphat”
Note: Edited some typos 02/15/07 BBN