The 12 links and the womb

I think I remember reading that the an unborn child or fetus exemplifies the nidanas in a different way to children and adults. Am I right that for Buddhists life begins at conception, but this "life" isn't fully conscious, because nama-rupa has not yet developed and so the concomitant links likewise? Or is the difference between a fetus and a baby more like the difference between a child and an adult?