Menstrual patterns in adolescent Swiss girls: a longitudinal study

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Abstract
Menstrual patterns were studied longitudinally in 140 adolescent Swiss girls. The mean cycle length was 32.2 (SD 11.24) d [days] in the 1st yr after menarche and 29.9 (SD 7.12) d in the 6th yr after menarche. The values of the mean cycle length became essentially constant from the 6th post-menarcheal year, the chronological age of 20 yr and the 36th post-menarcheal cycle. No association was found between cycle length and age at menarche. The menarcheal age of mothers and that of their daughters were significantly correlated with each other (r = 0.29, P < 0.001). The most frequent cycles of 21-27 and 28-34 d constituted 64-81% of all cycles depending on post-menarcheal age. short cycles (14-20 d), representing 2-6% of all cycles, were present in 14-31% of the girls; long cycles (35-41 d), constituting 10-16% of all cycles, occurred in 46-68% of the girls. The frequency of the long cycles tended to decrease at higher post-menarcheal ages. There were minimal changes in the duration of menstrual flow throughout the first 6 yr after menarche. The mean duration was 5.4 (SD 1.72) d for the 1st yr and 5.1 (SD 1.33) d for the 6th yr. The most frequent flow duration was 3-7 d, present in 88-94% of cycles. Prolonged bleeding tended to decrease with rising post-menarcheal and chronological age. The intensity of menstrual flow was mild in 11-16%, moderate in 62-78% and severe in 11-25% of the girls. The frequency of these 3 categories remained essentially unchanged during the first 5 post-menarcheal years.