London - When it comes to starting a family, size may really matter for men. Researchers have found that those who are infertile may also be less well-endowed.
The study, to be presented at the US conference, found infertile men are on average 0.4in (1cm) shorter than those who are fertile.
Men without reproductive problems had an average erect penis length of 5.3in (13.4 cm), while those in the infertile group measured 4.9in (12.5cm). The study looked at data on 815 men with fertility and other genital problems.
Research leader Dr Austen Slade, from the University of Utah, said: "This is the first study to identify an association between shorter penile length and male infertility. It's possibly a manifestation of congenital or genetic factors that predispose one to infertility."
But he added: "For now, men with shorter penises don't need to worry about fertility."
Another recent study found that men's sperm quality is falling every year, with experts fearing that modern life is destroying male fertility.
Fertility clinics found that the number of moving sperm - or "swimmers" - in men's samples has dropped by 1.8% each year.