Exposure to a combination of excessive stress and everyday chemicals whilst in the womb can have implications for future male fertility, according to Dr Amanda Drake and colleagues from the Centre for Cardiovascular Science and Reproductive Biology at the Queen's Medical Research Institute, University of Edinburgh.

Undescended testicles (cryptorchidism), misaligned urinary tracts (hypospadias) and low sperm counts are becoming much more common. Drake and her team link these three conditions to a syndrome called testicular dysgenesis syndrome (TDS), saying this is the result of reduced production or action of male sex hormones during a critical period of development.

Previous studies have found that between eight and 12 weeks into pregnancy is a crucial period for male reproductive development. During this timeframe, testosterone is produced, which affects development of male reproductive organs and fertility in later life.

Dr Drake and her group injected pregnant rats within this gestation period with either chemicals called phthalates; these are solvents used to soften plastic and can be found in a whole range of household products including shower curtains, credit cards and even children's toys, a stress hormone called dexaethasone or a combination of the two treatments.

The results, published in the journal Endocrinology, showed that giving the phthalates alone had an effect on fertility, whilst the stress hormone on its own did not. However, the researchers noted there was a further increase in fertility problems if the mother had been injected with both the stress hormone and the plastic chemical.

Drake has said these results could perhaps explain the reported recent increase in male infertility, as it takes into account chemical compound implications in conjunction with increases in stressful lifestyle factors.