Factors that affect male babies in the womb and in the first few years of life could have a significant impact on their future fertility, new research suggests.
Scientists at the University of Western Australia followed 423 men from the time they were in the womb until they were 20-22 years of age.
They observed that approximately one in six of the men had below-normal sperm parameters, with 14.8 per cent being below the threshold for normal volume of semen and 18.9 per cent being below the threshold for total sperm.
Factors that were associated with reduced semen parameters included adverse foetal growth and maternal smoking, while good childhood growth, height and lean body mass were linked with increased testicular volume.
The findings were presented at the annual meeting of the European Society of Human Reproduction and Embryology by Professor Roger Hart.
He said: '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 foetal growth and, in childhood and through adolescence, should be 'appropriately grown' - that is, neither underweight nor overweight.'