A Swedish study has identified for the first time a link between chlamydia infection and male infertility. The study of 244 couples, reported in Human Reproduction (May 2004), found decreased pregnancy rates in couples where men had IgG antibodies. These antibodies act as a marker of previous or persistent chlamydia infection. The results showed that, if a man was IgG-positive, the couple's chance of achieving pregnancy was lowered by 33%. The researchers recommended that testing for IgG in both men and women should be part of routine infertility examinations.