Could someone please explain this to me?

There's an interesting piece in the Telegraph by Professor Stuart Campbell, a London obstetrician who discusses his "technique for producing detailed 3D images of the developing foetus that show it smiling, yawning, rubbing its eyes and apparently 'walking' in the womb."

He continues:

"Though I perform these scans every day, I am still overcome by the excitement and the wonder of the foetus that is learning to be a baby. By 20 weeks it smiles, makes crying expressions and sucks its thumb. At 23 weeks, it begins to open its eyes and develops quite complex patterns of behaviour. It can survive outside the womb.

. . .

"I have been accused of sentimentality, but the fact is that, in these images, foetuses are baby-like. To me it is almost barbaric to abort foetuses between 20 and 24 weeks. In fact, the procedure is so unattractive and distressing that few doctors will perform the operation after 20 weeks."

Campbell, however, advocates reducing the amount of red tape involved in procuring an abortion during the first 12 weeks of pregnancy. (The current law in Great Britain requires two doctors to sign off in such cases, though in practice this is basically a formality, according to Campbell.) Here's his reasoning:

"Delay is bad. Anything that speeds up the process and enables an abortion to be carried out more expeditiously once a woman has made her decision, is to be welcomed.

. . .

"Some GPs are less keen on performing terminations than others. While they go through the laborious formalities of seeking independent signatures, a woman may be left waiting for two or three weeks before her termination. In that time, the foetus is acquiring the startling human characteristics seen in the scans carried out every day in hospitals around the country."

Now, correct me if I'm wrong, but the way I understand it, this obstetrician's position with respect to unborn babies is, Hurry up and kill it before it starts doing anything too cute that might convict my conscience!

I can't understand how anyone could be intellectually satisfied with such a position. Aborting a 20-to-24-week-old fetus is "almost barbaric," but aborting a less-than-20-week-old fetus is apparently morally neutral, a process to be streamlined? There's a very strange philosophical scheme at work here, one that establishes a firm chronological cut-off point for determining the humanity of an unborn baby, based largely on the emotional response the baby evokes.

Such a scheme seems, to me, intellectually unsustainable. What if you're faced with a particularly precocious 19-and-a-half-week-old fetus? Would aborting that baby be barbaric, or no? What is it, exactly, that happens at that magical 20-week threshold that universally transmogrifies non-humans into humans?

Is there an ontological difference between a 20-week-old fetus and a 19-week-old fetus? Between a 19-week-old and an 18-week-old? Between an 18-week-old and a 17-week-old, and so on?

Could someone please explain this to me?