Improvements in or relating to detection of impaired fertility

Disclosed is a method of detecting a retarded cycle in a human female subject experiencing same, the method comprising the steps of obtaining a sample of body fluid from the subject on each of a plurality of, but not less than three, days; testing each of the plurality of samples to determine the concentration therein of at least one analyte of significance in the ovulatory cycle; comparing a result determined from said testing with a predetermined threshold value; and, if said determined result is different from the threshold value; declaring the cycle, during which the samples were taken, to be a retarded cycle.