Page one of this link gives a simple overview of the process:
http://www.emedicinehealth.com/in_vitro_fertilization/article_em.htm
They don't really touch on the embryos that are discarded without any attempt at fertilization and I've don't have the time to search for that now. Suffice to say that there are usually embryos left over and they are usually destroyed. Also, some embryos that are implanted don't take. In addition, there is a procedure for reducing the number of viable implanted embryos if the woman chooses. I am puzzled that those who oppose stem cell research on thise particular embryos aren't outraged at the in vitro process in general.
You may be one who is and may state that later. And in my experience, you'd be the first that would be intellectually honest enough to do so.
Nevertheless, I do not hear hardline anti-abortionists opposing in vitro fertilization in the droves they oppose abortion. Again, I suspect that the numbers of dicarded embryos are far higher than the number of abortions that take place in this country.