A study presented on 23 June 2005 at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE) shows that men are overtaking women as the root of infertility in relationships. Factors such as declining sperm counts, obesity and smoking were largely to blame for the rise, which saw male causes creep from 50 to 51 per cent.

As well as lifestyle factors, experts said that men were becoming fathers at an older age as their partners delayed motherhood. Other studies presented at the conference this week have shown how the sperm of older men is at increased risk of DNA damage, making it less likely that fertilisation will occur.

Environmental factors are also considered to play an increasing role as the planet becomes more polluted and factors that disrupt the endocrine system are in the food chain.