As many as 1 in 5 pregnancies end in miscarriage. In 2% of these cases the women concerned suffer three or more consecutive miscarriages, many of them having no explanation. In August Human Reproduction Clemens Tempfer and colleagues, from the University of Vienna Medical School identify a variation in a nitric oxide synthase gene that could be at least partly to blame.

Tempfer et al. studied 105 women who had suffered unexplained recurrent miscarriages — that is, three or more consecutive losses before 20 weeks — and 91 postmenopausal women who had given birth twice and never had a miscarriage. Examining the genetic make-up of the women, they found a significant difference (P = 0.03) in the genotype frequencies for one variation of the NOS3 gene between the study and control group (Hum Repro 2001, 16:1644-1647).

Further analysis revealed that women with this genetic variation, which produces...