I remember looking up as the noisy family burst into the railway carriage – and immediately noticing that one of the boys had the unmistakable countenance created by an extra 21st chromosome, otherwise known as Down Syndrome. Unmistakable, yes, but I had never before seen the condition in the flesh, and felt a frisson of shock and discomfort.

That was 30 years ago. Today I have two children of my own, and the younger, Domenica, has Down Syndrome. Now, if I was sitting in a railway carriage, and another child with Down Syndrome were to come in, I would smile, rather than just stare. Yet nothing would have changed in those children: it is I who have changed.

It seems that this change is slowly happening on a national scale. Yesterday BBC Radio 4 broadcast Born With Down's, which revealed that for the first time there are more British children born annually with Down Syndrome than there were before widespread screening was introduced almost 20 years ago.

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According to Carol Boys, the chief executive of the Down Syndrome Association, there are several reasons for this. One is, frankly, startling: about 40 per cent of those who refused to terminate the pregnancy – after amniocentisis had detected the extra chromosome – did so because they didn't believe the diagnosis. That's as clear an indication as you could have of a generalised distrust of the medical profession, but it has little to do with attitudes to disability.

There are two other principal reasons given by Carol Boys, who herself is a mother of a man with Down Syndrome. One is that as children with the condition are now welcomed into the educational mainstream, rather than institutionalised, parents-to-be have been able to see with their own eyes that people with the condition are not uneducable fairground freaks. The second reason is linked to the fact that women are tending to have children later in life. Not only does this make them more painfully aware of the prospect of not being able to have any children at all; women who have a career of their own behind them are more likely to have the confidence not to be intimidated by doctors into having a eugenic termination.

For make no mistake: despite all the progress which children with Down Syndrome are now making in schools and homes up and down the country, the medical profession in general still has a visceral bias in favour of eugenic termination, which its practitioners are often startlingly crude in expressing. This is not based on a realistic and up-to-date assessment of the possibilities open to those with Down Syndrome, still less of the happiness which such people can and do bring to families and even communities as a whole: it is a function of the fact – which is undeniable – that people with Down Syndrome are likely to cost the NHS more in subsequent medical treatment than a child without any disabilities.

Yesterday the BBC News website ran a selection of comments on this issue by members of the public. One in particular, by Heather of Livingston, Scotland, is worth reproducing in full here: "I was told that my daughter had Down's when I was about 12 weeks pregnant and every doctor, gynaecologist I saw tried to convince me a termination was the best option. I was still offered this at 26 weeks! One reason given to me by a cold-hearted consultant was that 'these babies put a strain on the NHS'. My daughter was stillborn and when pregnant again, I refused all tests apart from a scan. It's not society who are looking for the 'perfect baby', it's the medical profession."

Thirteen years ago, our own decision not to find out whether our unborn child was "perfect" or not provoked a similar comment from the ex-nurse and agony aunt, Claire Rayner. She wrote that the Lawsons had behaved selfishly, because of the "misery" and cost to society of such children: "People who are not yet parents should ask if they have the right to inflict such burdens on others." This, of course, is the classic eugenic argument, which was taken to its logical conclusion in Germany 70 or so years ago. Astound-ingly, Claire Rayner was at the time of those remarks a patron of the Down's Syndrome Association – a position which was instantly terminated by an outraged Carol Boys.

Yesterday I spoke to Carol after she had appeared on Woman's Hour with Joanie Dimavicius of the NHS Down Syndrome screening programme. Carol said she had the impression that Dimavicius was distinctly unsettled by the figures which showed that an increasing number of women were resisting the pressure to abort babies diagnosed with Down's.

If Ms Dimavicius is uneasy about this trend, it would hardly be surprising. After all, the NHS Down Syndrome screening process is hugely expensive, justifiable on cost-benefit grounds purely on the basis that it will detect and destroy children who would otherwise cost the Health Service much more as survivors. If there are now more children born each year with Down's than there were before the national screening programme was introduced, then Ms Dimavicius might be wondering how much her own job is worth to society.

This question is all the more pertinent because the NHS does not factor into its life-or-death calculus the fact that every year hundreds of children without any disability are lost as a direct result of amniocentesis, which carries with it a 1 per cent risk of miscarriage. The other invasive test, Chorionic villus sampling (CVS), carries a 2 per cent risk of miscarriage. Given the huge numbers of "false positives" in the initial scanning process, this has resulted in some very disturbing statistics from the National Down Syndrome Cytogenetic Register, which were unearthed last July by the Down Syndrome Educational Trust.

The Register shows that in 2006 – the last year for which results are published – 400 babies without Down Syndrome were "lost", in order to "prevent" 691 births of babies with the condition. Just pause for a second to take in the human misery captured in this remarkable statistic, and include in it the misery of those who terminated an "imperfect" child, and later bitterly regretted the choice they had made.

Victoria Lambert wrote a very affecting piece in The Sunday Times last weekend, on her decision to abort a baby diagnosed with Patau Syndrome, a chromosomal abnormality which results in a very short natural lifespan: "What I often think is that if my son had been born alive and perhaps with two years to live, were those not two years of my life that I could have spared to nurse him? Would it really have been such a big deal? With hindsight, I think I could have offered that at the very least to a child I had wanted so much."

Yes, there are arguments about the quality of life a disabled child can have. The truth, however, is that a congenitally disabled person knows no other existence than that which he or she has: it is others who might deem their lives to be inadequate, not they. When I look at Domenica I see someone with a vast joy in just being alive, and I am indescribably happy that she is.