Can you tell me how soon after conception our hearts begin to beat? I saw my daughter's heart beating in utero at six weeks: a tiny light flashing on and off. Since then I've often wondered if our hearts are created at the moment of conception. And if not, how does such a vital organ evolve? Thanks for any enlightenment. It's funny what we spend time wondering about. My daughter is now 7 years old! - L.
Unbelievable as it is, an embryo starts life on Day 1 as a simple cell, a fertilised egg, without any of the special features that make us unique, except for the blueprint that guides it all, our DNA. No heart, no organs. It is smaller than a grain of salt, rolling down the fallopian tubes dividing madly, then implanting in the uterus or womb at about 7 days old. The cells divide: one, two, four, eight, 16, 32, 64 ... right up to 37 trillion in adulthood.
But before that, at 21 days, the heartbeat begins - except it's not really a heart yet. Our genes have dictated which cells are made, how they specialise, and to where they migrate. These collections of cells form two simple blood vessels that sit side-by-side, then fuse together, thicken and bulge. Specialised electricity-generating cells have already migrated to the right location on the tube. At 21 days, these cells start pulsing, and the heart tube starts beating. Three days later, the tube folds over twice, does a half-twist and assumes the rounded shape of a normal human heart.
When it doesn't all go to plan, the infant can be born with a cardiac abnormality. One in every hundred people has a bicuspid aortic valve, the most common congenital cardiac malformation, where the valve has two leaflets instead of three. More severe anomalies can result in miscarriages.
Because organ development happens largely in the first two months of pregnancy, many of these women won't even realise they were pregnant, let alone that they've miscarried. The best estimates are that more than 30 per cent of all pregnancies end up in miscarriage, but only about half of those are actually noticed by the women themselves.
