Age and seasonal distribution of menarche in Korean girls

This paper examines the menarchal age of Korean girls and its monthly distribution to define the possible relationship between menarche and season. Menarchal age is influenced by diverse factors such as hereditary, geography, climate, psychological factors, socioeconomic status, body weight and height, nutritional state, body fat and exercise as well as the presence of chronic illness. In Korea, there is evidence of secular change toward earlier menarchal age, where the average menarchal age was 14.8 in 1952, 14.4 years in 1979, 13.4 years in 1986, and 12.5 years in 1988. A cross-sectional study was conducted from July 1993 to July 1995 among 4237 female middle and high school students, aged 14-20 years, in Ansan, Korea, to obtain data on demographic characteristics, menarchal age, month of menarche, and the menarchal age of the participant's mother. Findings revealed that average menarchal age is 12.5 years for the girls and 15.4 +or- 2.3 years for their mothers. Menarche is most common in August and January (summer), January and December (winter) in decreasing order. Seasonal pattern of menarche may also be related to the psychological factors during school vacation such as relaxation, decrease stress from studies, and/or physical rest.