You know as an IVF Mom I had the fortunate experience of actually feeling the 'spark of life or conception" when I believe the egg implanted and the work really began creating my daughter. Because you learn so much about timing doing IVF & since we used assisted fertilization I knew of course the date but also the time of "Hi Egg, its me Sperm, 'Sup?" After that its waiting for the first time you can reasonable expect to take a pg test that would be valid. I had calculated the day I was likely to implant or not after counting out from embryo placement (again- knew the day and time) and was in my office in a Mommy chat room when I literally felt a tiny electric current in my core, seriously like a spark or 'ping' and as I stilled to think about it I felt a very, very mild flush go through my body and suddenly I was starving like someone coming off of a 3 day fast. Just instant, terrifying, panicky, desperate STARVING. I ran into the kitchen and shoved food in. It was AMAZING.

Actually the spark would have occurred at the point when the egg would meet the sperm, i.e. in a dish in a lab. Because when it was implanted in your body, it was already fertilized. Perhaps it was another spark when it was attaching to the wall of the uterus?