In all my searching, I have found no studies that support the notion that Plan B acts as an abortifacient. The only two proven methods of action are thickening of the cervical fluid and prevention of ovulation. The manufacturer of Plan B states that it may interefere with implantation, but I strongly suspect that they’re just covering their ass…ets.
"Over the past few years, reproductive physiologist Horacio B. Croxatto of the Chilean Institute for Reproductive Medicine in Santiago, Chile, and his colleagues have studied the effects of levonorgestrel [the active ingredient in Plan B] on the reproductive cycles of female rats, monkeys, and humans. Croxatto and one of his study partners, biomedical researcher Vivian Brache of PROFAMILIA in Santo Domingo, Dominican Republic, are members of the ICCR."
"Croxatto and his colleagues exposed female rats to very high doses of levonorgestrel at various stages of their reproductive cycles, either before or after ovulation or before or after mating. The researchers found that levonorgestrel inhibited ovulation totally or partially, depending on the timing of treatment and the dose administered. However, the drug had no effect on fertilization or implantation. This research was published in the May 2003 issue of the journal Contraception."
"Next, Croxatto and his colleagues studied the effects of levonorgestrel given to Cebus monkeys either before ovulation or postcoitally. The reproductive cycle of each animal was monitored by ultrasound examination of the ovaries, vaginal smears, and measurements of blood hormone levels, in order to time the administration of levonorgestrel. The researchers found that, when given before ovulation, levonorgestrel was able to inhibit or postpone ovulation. Alternatively, when it was given after mating—at a time when fertilization was believed to have occurred (on the basis of previous monitoring)—the pregnancy rates observed were identical in cycles treated with levonorgestrel or with a placebo. This indicates that levonorgestrel did not interfere with any postfertilization process required for embryo implantation. This research was published in the June 2004 issue of the journal Human Reproduction."
"[...]Croxatto, Brache, and their colleagues studied the effects of levonorgestrel administered during this fertile preovulatory period of women’s menstrual cycles. The researchers used Plan B®, a levonorgestrel-containing emergency contraceptive product marketed in the United States and Canada."
"Twenty-nine women in Santiago and 29 women in Santo Domingo were enrolled in the study. All of the women were protected from pregnancy by tubal ligation or a nonhormonal intrauterine device. The study was randomized, double-blind, and placebo-controlled. Women were treated with either a placebo, a full dose of Plan B emergency contraception, or a half dose of the drug. They were followed over several menstrual cycles and, by the end of the study, each woman had received all three of these treatments, separated by resting cycles. The women were randomly assigned to receive the treatments at specific times during the fertile preovulatory period, according to the diameter of the leading ovarian follicle, as determined by ultrasound. The leading ovarian follicle is the structure that ruptures to release the egg."
"In 82 percent of Plan B–treated cycles, follicles failed to rupture within the five-day period following treatment (the maximum time span sperm would survive in the female reproductive tract), or there was some significant abnormality in ovulation. These conditions occurred in only 41 percent of placebo cycles. The rate of failed or abnormal ovulation that was observed with Plan B treatment is identical with the estimated efficacy rate of Plan B emergency contraception. Blood tests on these women indicated that Plan B influences ovulation by suppressing the surge of luteinizing hormone (LH), the hormone that triggers ovulation."
"’There is no doubt that fertilization would not have taken place in those women should they have had intercourse prior to treatment,’ says Croxatto. ‘We conclude that the effects exerted by Plan B, when it is taken before the onset of the LH surge, may fully explain the pregnancies averted by emergency contraception. Failure to affect the LH surge, because treatment was begun too late in the fertile preovulatory period, explains the 20 percent failure rate of this method. Our data presented in this paper suggest that emergency contraception using levonorgestrel works by disrupting ovulation, not by interfering with implantation.’ This research was published in the December 2004 issue of the journal Contraception."
Can I say definitively that Plan B does not interfere with implantation? No. Do I believe that the evidence against it acting in that manner is sufficient to call the drug contraceptive rather than abortifacient? Yes. If someone can provide research that shows a link between Plan B and spontaneous abortion, I’ll be glad to look at it. In the meantime, I’m with this guy:
"’The post-fertilization effect was purely a speculation that became truth by repetition,’ says Joe DeCook, MD, a retired OB/GYN and vice president of the American Association of Pro-Life Obstetricians and Gynecologists. ‘In our group the feelings are split. We say it should be each doctor’s own decision, because there is no proof.’"
So, what have we learned today?
- Breastfeeding prevents pregnancy via increased levels of prolactin, not progesterone.
- Prolactin does not affect the endometrium, so it does not affect implantation.
- There is no evidence that Plan B affects implantation.
- There is evidence that suggests that Plan B only prevents conception by either making cervical mucus hostile to sperm or preventing ovulation.
- Being liberal or conservative does not make one immune to stupidity or ignorance.