|See part 1 of V's guest commentary.|
Day 5. What does that tell us about where these embryos are in the overall scheme of things? Well, the opponents to ES cell research (and the morning-after pill) claim that life begins when the male and female gametes unite (to form a zygote, which will then become an embryo, which will in turn become a fetus). I can see how that can be a tremendously seductive idea---it is a clear, unambiguous time point that defines an event. But what event? Medically, the event is 'fertilization' but it is commonly referred to as "conception"----the dictionary allows that the terms may be synonymous in this context. Not to get too semantic, but I think this is part of the problem. The term conception brings about images of a child. But when you fertilize a garden you do not create life---rather, you create conditions conducive to life. Anyways, I think it is incorrect to think of fertilization as conception (in the popular sense and understanding) for the simple reason that an embryo has a ZERO chance of becoming a human being until it implants in the uterus of the mother ----and implantation doesn’t generally start till day 7 and complete till day 12. This is where it gets interesting. I will not go into scientific detail---suffice it to say that pregnancy requires a confluence of finely tuned events in the mother as well as in the embryo. Just bombarding a uterus with zygotes will not do it. Stats on embryo implantation [from In Vitro Fertilization (IVF) studies] reveal that a majority of embryos do not implant in the mother---in fact an overwhelming majority of these embryos cannot produce successful pregnancies (the global success rate is something like 15%. Even with the best technologies and circumstances the best we can do is about 35%, according to a 2005 CDC report. Also, frozen embryos do consistently worse than fresh embryos). IVF stats are very relevant in this discussion because frozen IVF embryos are at the core of the ES Cell debate. But even if one were to look at this phenomenon in natural settings, the picture is not much different. It has been estimated that 50- 70% of all fertilized ova are lost at or before implantation, before the woman even realizes she is pregnant.
Later today: Part 3, What are the chances?
Tags: Stem Cells, Science, Politics, IVF, Bush, Tony Snow, Snowflake babies