Pattern of menstrual cycle length in south Indian women: a prospective study
Jeyaseelan, L.; Antonisamy, B.; Rao, P.S.
Social Biology 39(3-4): 306-309
1992
ISSN/ISBN: 0037-766X PMID: 1340049 DOI: 10.1080/19485565.1992.9988826Document Number: 329646
Between 1969 and 1974, a community survey consisted of following 1740 currently married women living in urban and rural areas in North Arcot district in Tamil Nadu, India, for 8308 cycles to examine the association between age and menstrual cycle length. Interviewers went to the homes of the women every 5 weeks. Mean cycle length by age of women was 31.2 days, with a standard deviation (SD) of 3.2 days. 39% of the women had a mean cycle length of more than 32 days. 60% had mean cycle lengths ranging from 25-31 days. Mean menstrual cycle length among the 8308 cycle lengths was 31.8 days with a SD of 6.7 days. This mean cycle length was considerably different from that of earlier studies. The most frequent cycle length was 30 days. 43% of cycle lengths were more than 31 days. 47% were between 25-31 days. 28-day cycles occurred in no more than 9% of the women regardless of age. Variation of cycle lengths was greatest following menarche (SD - 5.6 days for women = or 19 years old). The variability fell during the main reproductive years (SD = 3.2 days for 20-24 year olds and 2.8 days for 25-29 year olds) and began to climb as women approached menopause (SD = 2.9 days for 30-34 year olds and 4.8 days for women = or 35 years old). These findings indicated that menstrual cycle lengths of between 25 and 40 days were normal. The researchers believed that the 28-day cycle is not the norm, particularly in developing countries. They suggested that clinicians should reconsider the decision-making process currently used when determining menstrual cycle abnormality based on a 28-day-cycle norm. These findings are especially important in regards to women applying the rhythm or natural family planning methods.