HEALTH / SECOND OPINION

MEDICAL experts seem unable to agree whether or not men in western countries are becoming less fertile. A report from Denmark published in the British Medical Journal in 1992 claimed that sperm counts had fallen by 40 per cent in the past 50 years, and this led to worries about the use of sex hormones in agriculture and other environmental toxins. But since then - as is so often the case - other experts have criticised the original findings on statistical and other grounds. In early July the Danish doctors reiterated that 'the evidence cannot lead us to a conclusion other than that sperm counts are lower than they were in the 1940s and 1950s.'

Is infertility a growing problem? What seems to be a simple question is proving remarkably hard to answer. In Britain and other advanced countries, more couples are coming to infertility clinics for treatment, but this is to be expected since so much publicity has been given to the real advances made in what can be done for them. Tests for the causes of infertility are more precise, the drugs are more effective, and many couples can be helped to conceive through in vitro fertilisation (IVF) and gamete intrafallopian transfer (GIFT), developed from test-tube baby research.

The data from infertility clinics show, however, that couples being treated now are older than in the past. Women are delaying ever longer before having their families, and so are older when they discover that having a baby is not simply a matter of stopping contraception. Women having their first babies in 1990 were two to three years older on average than those having children in 1970 - indeed, if present trends continue, the average age at which western women have children may have risen to 30 by the next century.

This trend is important because the likelihood of a woman in a stable sexual relationship becoming pregnant shows little change during her twenties. After that it starts to decline, and then falls rapidly after the age of 35. Reliable data on the effect of age have come from IVF clinics: the pregnancy rate after transfer of a single embryo in a natural cycle is, according to a recent Lancet review, 17 per cent for women under the age of 30, 13 per cent for those aged 31-35, and 11 per cent for those aged 36-40.

Age is, indeed, probably the most important single factor determining fertility. Teenagers have high sex drives, their sex organs are firing on all cylinders, and they are usually free of disease. Worldwide, the most important cause of infertility in women is damage to the fallopian tubes (which transport the ova from the ovaries to the uterus) from sexually transmitted infections such as chlamydia and gonorrhoea. Men, too, may become infertile from sexually transmitted diseases as well as from drug treatments for cancer and chronic diseases such as ulcerative colitis, from misuse of anabolic steroids, from exposure at work to pesticides, heavy metals and many other chemicals, and from regular heavy drinking.

In both men and women infertility often goes unexplained, and many of the common causes are difficult to treat. Even with all the technical advances available, many couples coming for treatment are disappointed. Donation of sperm or ova help a few, but all the techniques of assisted conception are expensive and few couples can afford repeated attempts.

Infertility would be a much smaller problem in a society in which couples expected to have their children before the age of 25. Many more families would then experience the pleasures of

watching their grandchildren and great-grandchildren grow up. The wide availability of

contraception methods may have given us greater sexual freedom, but the postponing of parenthood to the biological limits makes poor social sense as well as poor medical sense.