Menarcheal age in Oslo during the last 140 years.

Data from maternity clinics have been used to study the trend in menarcheal age among girls born in Oslo after 1840. The investigation was based on recordings from approximately 50 women from each year. The women were divided into social categories according to their own or their husband's occupation. The results show a trend toward earlier maturation within the working class, which is characterized by two periods of rapid fall in menarcheal age. The first period covers women born between 1860 and 1880, and shows a fall in menarcheal age from about 15.6 to about 14.6 years. During the second period of rapid fall, which covers women born between 1905 and 1940, the menarcheal age was further reduced from about 14.6 to 13.3 years. The age at menarche has been stable at about 13.3 years for women born after 1940. These results contrast with those of some earlier studies of the menarcheal age in Norway. However, it is shown that the discrepancies between these investigations and our own disappear when the same computational methods and the same interpretation of the age recordings are used.