The objective of the study was to analyze the relationship between seasonal variation and menarcheal occurrence. The total number of 1,026 girls was drawn from 15 classes of a high school (2nd grade) in Seoul. The distribution of birth year in total subject were 2.5 percent in 1974, 76.6 percent in 1975 and 20.9 percent in 1976.
1. The highest proportion in the distribution of menarche month was August (16.0 percent), and 14.2 percent in December, 12.0 percent in October. On the otherhand the incidence of menarche from February to July was low level at 3 to 6 percent. The first order of the menarche month during 12 birth months was August (mean order : 1.75), and 2nd in December (2.83), 2nd in October, 4th in July and 5th in January. The last rank of menarche month was February and April.
2. In the incidence rate of menarcheal month by the born month, there was not significance statistically in girls born in April, May, June and September, and was significance statistically in girls born in the other months. In the seasonal patterns of menarche occurrence, girls born in spring, summer and winter had the highest incidence rate of menarche in summer, and girls born in autumn had a tendency to occur more frequently in autumn. Season of birth was no significance associated with season of menarche(x²=15.90360 P value=0.0689).
3. The mean age of menarche in total subject was 13.44, and the mean menarcheal age by the season of birth was 13.35 in winter, 13.37 in autumn, 13.47 in summer and 13.56 in autumn, Girls born in March reached their menarche about 6 months later than those born in December. There were no significance between the menarcheal age and season or month of birth.
4. Under the assumption that the menarcheal age occur later from 1 month to 11 months than real menarcheal age, the peak distribution of menarche occurrence by the season change with a cyclic pattern.
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