A decline and a halt in mean age at menarche in Iceland.

Mean age at menarche has been declining in many countries during the past hundred years. Reports of a halt in this trend have come from Oslo and London. In this study the trend in age at menarche in successive birth cohorts, starting in 1900, was investigated for the first time in Iceland. This was based on recall data obtained as part of a cervical cancer screening programme covering the whole country. Around 78% of the female population at the ages targeted for screening responded to questions on reproductive factors in the years 1964-89, or over 73,000 women aged 20-69 years. Investigation of the validity and reliability indicated that the estimated mean age is likely to be unbiased, and that for 90% of the women the information was reliable. Mean age at menarche declined from 14.9 years to 13.5 years in successive cohorts of Icelandic women born 1900 to around 1950. In cohorts born 1951-67 the mean age has remained stable. The halt appeared later than reported from Oslo and London and at a higher age.