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Originally posted by Dalaena
I'm not sure if this is relavent at all, but in Plan B, there COULD already be a baby. We are simply preventing that baby from actually growing. The Morning After pill thickens the uterine wall, making it impossible for the zygote to implant itself. Technically, there is a baby because the sperm and the egg has already met to form the zygote, but the pill keeps the cells from attaching to the uterine wall.
According to
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Croxatto and his colleagues exposed female rats to very high doses of levonorgestrel at various stages in their reproductive cycle, either before or after ovulation or before or after mating. “When a woman uses emergency contraception,” Croxatto explained, “she does not know whether she is taking the pills before or after ovulation or before or after fertilization.” 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 when it was administered shortly before or after mating or before implantation.
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.
However, Wikipedia reports, "these studies have also shown that, in women who ovulate despite taking ECP before ovulation, there are changes in certain hormones such as progesterone and in the length of their luteal phase.[4] These secondary changes might inhibit implantation in cases where fertilization occurs despite ECP use. Because of the difficulty of studying pre-implanted embryos inside the uterus and fallopian tubes, both sides of this debate concede that completely proving or disproving the theory may be impossible.[28][2].