Secular trends in age at menarche in Norwegians born from 1840 to 2008

It is uncertain if age of menarche continues to decline. There has been no systematic meta-analysis of ages at menarche in Norway the past three decades. To conduct a systematic review and meta-analysis to assess secular trends in menarcheal age in Norway. A literature search was performed in PubMed, Web of Science, and Embase to identify studies including ages at menarche from healthy females. Re-analysis of data from 16 surveys were included together with 17 published studies in a meta-analysis using weighted regression analyses with fitted restricted cubic splines. Each study or dataset was given a random intercept to account for within-survey correlation. In total, 783,757 observations were included in the meta-analysis. Three distinct periods were identified. For women born 1840–1910, a large and stable decline with −0.14 to −0.20 years per decade (y/d) was observed, whilst in women born 1910–1950 this decline accelerated up to −0.30 y/d. The third period of women born 1950–2008 saw a small and stable decline with −0.06 to −0.08 y/d. Age at menarche declined throughout the study period from 1840–2008, but more rapidly in girls born between 1910–1950. Data suggest an ongoing, modest decline.