"After the egg is released, it moves into the fallopian tube. It stay there for about 24 hours, waiting for a single sperm to fertilize it...At the instant of fertilization, your baby's genes and sex are set...within 24 hours of being fertilized it starts dividing very fast into many cells...Within three weeks, the cells begin to grow as clumps, and the baby's first nerve cells have already formed." http://www.webmd.com/baby/guide/understanding-conception
"The fetal heartbeat starts beating during the embryonic stage of pregnancy at 22 days after conception" Read more: About the Fetal Heartbeat | eHow.com
That 22 day heart beat is roughly 8 days after the missed menstrual cycle HCG Pregnancy hormone has detectable for 2 or 3 weeks.
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