A new study by University of Western Australia (UWA) researchers blamed the lower sperm count to their mother's smoking while pregnant.

Other studies have shown that smoking while pregnant has other effects on the fetus.

However, besides the nicotine habit, UWA Professor of Reproductive Medicine Roger Hart said at the yearly meeting of the European Society of Human Reproduction and Embryology in London, other factors behind the lower sperm count are poor fetal growth, poor childhood growth patterns, increased fat deposit during adolescence and smoking and drug use during adult years.

"The main message from our study is that to reach adulthood with the best possible testicular function a man should not be exposed to his mother's smoking, should have good fetal growth and, in childhood and through adolescence, should be 'appropriately grown' - that is, neither underweight nor overweight - and as an adult should not smoke or take drugs," said Mr Hart, also the medical director of Fertility Specialists of Western Australia in Perth.

His study found the one in six men studied had sperm counts lower than the normal threshold as defined by the World Health Organisation (WHO). Another 26.4 per cent had sperm with appearance that failed to meet WHO criteria.

The study is a follow up to a 1989 WA study that had 2,900 pregnant women as respondents and their babies which were monitored for fetal growth, and 423 of their male children who became adult after 20 years. It measured the men's testicular volume, analysed their sperm quality and hormone production and body composition for fat distribution.

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