Professor Hart, who reported his findings yesterday at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in London, said poor fetal growth, exposure to maternal smoking, poor childhood growth patterns, increased fat deposition in adolescence, and smoking and drug use in adulthood may ultimately lead to a poorer sperm outlook.
"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," he said.
The study was based on a follow-up of the Western Australian Pregnancy (Raine) Cohort, which began in 1989 with the enrolment of 2900 mothers during pregnancy and involved regular assessment of their babies from birth, including fetal growth measurements.
Part of the 20-year follow-up of this cohort (in 423 of the men at the age of 20-22 years) involved a testicular assessment, which included measurement of testicular volume, analysis of semen quality and hormone production, as well as body composition for fat distribution.
Results showed that around one in six of the men tested had sperm parameters below the "normal" threshold recently defined by the World Health Organization (WHO). In addition, a quarter of the subjects (26.4 per cent) had sperm whose appearance did not meet the WHO's acceptable criteria.
When these results were matched with the earlier fetal growth assessments, being consistently small in utero was associated with a significantly greater chance of having a sperm assessment within the lowest quartile of all the men assessed, while men with good intrauterine growth were less likely to be in this lowest quartile of sperm production in adulthood.
Being exposed to their mothers' smoking (18.6 per cent of men) was also associated with lower sperm production. Increased testicular volume was linked to childhood growth, height and total lean body mass.