(excerpt) An ultrasound video of an unborn child sucking its thumb makes a case against abortion that reason hardly need supplement. But a zygote photographed just after an in vitro conception is not so easily recognizable as a human being or person. Pro-lifers often assume that this difficulty has been overcome by modern science. Since the 1820s, when evidence of ovular fertilization first became known, it has been clear that the life of a human being runs from conception to death.
Stith, Richard, "Facing the Unborn" (2015). Law Faculty Publications. 343.