- Email: [email protected]
Menstrual bleeding patterns in untreated women
ELSEVIER
Menstrual Untreated Elizabeth M. Belsey,t* Fertility Regulation?
Bleeding Patterns in Women Alain P.Y. Pinol,t and Task Force on Long-Acting
Menstrual histories recorded by more than 1000 healthy, untreated women have been analyzed using the reference period method. Results were obtained for each year of age from 15 to 49. Between menarche and age 19, the most important feature of menstrual patterns is their variability. Within-woman mean segment (cycle) length then decreasesslowly but steadily, from 29.0 days at age20 to 26.7 days at age 40. The range of segment lengths over a year also falls, to a minimum of 7 days at age 38. During the 40s mean segment length rises to 29 days at age 49, and there is a sharp increasein the range, to 28 days. The length and variability of bleeding episodes, however, changes little between the ages of 19 and 49. Modifications to the World Health Organization definitions of ‘clinically important’ bleeding patterns are proposed. 0 1997 Elsevier Science Inc. All rights reserved. CONTRACEPTION 1997;55:57-65
menstrual bleeding patterns, clinically tant patterns, reference period analysis
KEY WORDS:
impor-
Introduction uring the 19305 Dr Alan Treloar and his coworkers at the University of Minnesota started to collect information which would enable them to describe the length and variability of the menstrual cycle. Female students entering the University between 1935 and 1938 were asked to complete a calendar-year record showing the beginning and ending date of each menstrual period. At the end of the year, the completed records were collected, and the participants were issued with a new record card for the following year. When they had completed their studies, contact with the women was main-
D
TSpecial Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, 1211 Geneva 27, Switzerland Name and address for correspondence: Dr. C. d’Arcangues, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organizatron, 1211 Geneva 27, Switzerland. Tel: (41 22) 791 21 11; Fax: (41 22) 7914171 Submitted for publication August 30, 1996 Revised November 13. 1996 Accepted for publication November 13, 1996 ‘Present address: SigmaPlus, 10 rue de la Rigolette, 1266 Duillier, Switzerland
0 1997 Elsevier Science Inc. All rights reserved, 655 Avenue of the Americas, New York, NY 10010
Systemic Agents for
tained annually by mail. Data collection continued for over 40 years; in time, some of the original participants’ daughters, other female relatives, and family friends were also enrolled in the study, as they reached menarche. Some of the results from the study were published in 1967.l At that time, the dataset included information on more than 275,000 menstrual cycles, recorded by 2700 women over a total of 25,800 years. Because of its size, the lengths of some of the menstrual histories, and the fact that participants in the study were normally menstruating women, the dataset is unique. The World Health Organization (WHO) Task Force on Long-Acting Systemic Agents for Fertility Regulation therefore requested, and obtained, a copy of part of the dataset from the Tremin Trust at the College of Nursing, University of Utah, where it is now housed. The objective of the analyses reported below was to describe bleeding patterns in ‘normal,’ untreated women, using the techniques of analysis recommended by WHO,2 so as to provide baseline data with which the patterns observed in women using hormonal or mechanical methods of contraception could be compared.
Methods The Dataset The dataset originally consisted of a series of chronological event codes with corresponding dates. The majority of these events were menstrual (either the start or end of menses). Other events coded included menarche, marriage, births, hormone therapy, gynecological surgery, and menstrual disorders. Breaks in recording were also noted. The dataset made available to WHO included records kept by 1109 women. Fifty-nine of these were excluded from analysis because their date of birth was unknown. The menstrual event codes and dates were then converted into a menstrual diary for each remaining woman, and the diaries were divided into calendar years. In total, there were records for all or part of 16,803 woman-years. Of these, 10,428 years or ISSN OOlO-7624/97/$17.00 PI I SO01 O-7624(96)00273-9
58
Belsey et al
part-years were excluded from analysis: 5269 were incomplete (due to menarche, menopause, or, more usually, a break in record-keeping); 1761 included some part or all of a pregnancy, and another 717 followed a year in which a pregnancy ended and thus could have included a period of post-partum amenorrhea or lactation (which were not included in the coded events); hormone therapy, gynecological surgery (dilatation and curettage or hysterectomy) or menstrual disorders were recorded in 1034; in 1115 there were obvious errors in recording (for example, two consecutive dates of onset of menses with no intervening date of end of menses); and 532 were recorded by girls aged less than 15 or women aged 50 or over. This left 6375 complete years in healthy, normally menstruating women of reproductive age.
Description of Menstrual Bleeding Patterns The reference period method3 was used to analyze the menstrual diary records. Days within a menstrual event were defined as bleeding days, and days outside menstrual events were defined as bleeding-free days. A bleeding episode was defined as any set of one or more bleeding days (either consecutive or separated by only one bleeding-free day) bounded at each end by two or more bleeding-free days. A bleeding-free interval was defined as any set of two or more consecutive bleeding-free days bounded by bleeding days. (Thus, a single bleeding-free day was treated as part of the bleeding episode surrounding it, in accordance with Treloar and co-workers’ own definitions’ and with previous reports of bleeding patterns in contracepting women.4-6) A bleeding segment was defined as the sum of a bleeding episode and the immediately following bleeding-free interval. Calendar-year reference periods were used for the majority of analyses. Each bleeding event (episode, interval, or segment) was assigned to the year in which it started, even if it ended in the subsequent year. The following bleeding pattern indices were calculated for each woman-year: the numbers of bleeding days and bleeding episodes begun, and the mean, range, minimum, and maximum values of bleeding episode, bleeding-free interval, and segment lengths. The range of episode (or interval/segment) lengths, defined as the difference between the longest and the shortest, could only be calculated if at least two episodes (or intervals/segments) started during the year. The numbers of bleeding days and episodes were then multiplied by 90/365 so that they relate to a 90-day reference period. Additionally, the first 360 days in each year were divided into four 90-day reference periods, and the same indices were calculated for each period. The pe-
Contraception 19973557-65
riods were then divided into six subgroups, according to which of the following ‘clinically important’ bleeding patterns (as defined by WH02) had occurred: 1. Amenorrhea: no bleeding during the reference period 2. Infrequent bleeding: fewer than 3 bleeding episodes 3. Frequent bleeding: more than 5 bleeding episodes 4. Irregular bleeding: between 3 and 5 episodes with less than 3 bleeding-free intervals of length 14 days or more 5. Prolonged bleeding: 1 or more bleeding episodes lasting 14 days or more 6. None of the above: a ‘normal’ bleeding pattern. Statistical Methods Each woman-year was classified according to the age of the woman attained during that year. For each single-year age group, the bleeding pattern indices were summarized by calculating the median, and the 5th, 25th, 75th, and 95th percentiles.
Results Between 190 and 299 calendar-year diaries were available for analysis for each single year of age from 19 to 36 years. The minimum number of diaries included in analysis, at age 49 years, was 89. The number of bleeding days recorded over 90 days, according to the age of the woman, is shown in Figure 1. The median value is 19 days for all but one of the single-year age groups between 15 and 34, increases to 20 days between the ages of 35 and 45 years, and then falls to 18 days by age 48. In the age range 20-34 years, at most, 10% of women have less than 11 or more than 26 bleeding days per 90&y period. The variability between women increases thereafter, particularly at the lower end of the distribution, and at age 49, 25% of women have less than 10 bleeding days in every 90. The median number of bleeding episodes increases from 2.7 per 90 days at age 15 years to 3.2 at age 21, remains constant over the next two decades of reproductive life, increases again to 3.4 at age 40, and finally falls, from age 46 onward, to 2.9 at age 49 (Figure 2). There is very little variation between women, even at the lower and upper ends of the age range. Between the ages of 22 and 41 years, 90% of women have no fewer than 2.0 and no more than 3.6 episodes every 90 days. The median value of the mean length of bleeding episodes starts at 6.6 days at 15 years of age, and falls to 6.0 days by age 21 where, with minor variations, it remains unchanged until age 49 (Figure 3). Less than
Contraception 1997;55:5745
Menstrual Bleeding Patterns
59
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Belsey et al.
Contraception 199755~57-65
3.5 15
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5% of women have bleeding episodes the average length of which are less than 4 days; at the other end of the spectrum, only 5% have episodes with an average length of 8 days or more. Within-woman, episodes vary little in length. At least 25% and, in some single-year age groups, more than 50% of women, have episodes which differ in length by only 1 day over a year (data not shown). At ages 15-43 years, three-quarters of women have no more than a &day variation in the lengths of their episodes. Variability increases slightly after age 44 but even then, 75% of women have only a 4-5 day difference between their shortest and longest episodes. At least 95 % of women of all ages have a minimum episode length of 3 days, while the maximum length has a median value of 7-8 days, an upper quartile of 8-10 days, and a 95th percentile of 9-12 days until age 40 and 12-17 days thereafter (data not shown). Figure 4 shows the within-woman mean length of bleeding-free intervals. The median value decreases steadily from 25 days at age 15 years to a minimum of 20 days at age 41, and then increases to 23 days at age 49. At all ages, at least 5% of women have intervals with an average length of only 17-18 days. At age 15 years, the median value of the range of bleeding-free interval
lengths is 18 days, and 25% of
girls have intervals which vary by 34 days or more (Figure 5). Variability in the lengths of bleeding-free intervals then decreases, and is at its lowest in the age range 23-41 years. Even in these middle years, however, one-half of women have a range of 7 days or more, and 25% have one of at least 13 days. In the pre-menopausal years, variability increases again, and at age 49,50% of women have bleeding-free intervals which differ by at least 28 days, and 5% have a range of approximately 6 months. Figure 6 shows the distributions of the withinwoman mean segment length for each year of age. The changes with increasing age follow the same pattern as the mean bleeding-free interval: the median value falls from 32 days at age 15 years to 27 days at age 41, and then rises to 29 days at age 49. Although there are some extreme values in each single-year age group, there is, in general, relatively little variation between women. Between the ages of 21 and 41 years, the interquartile range is only 3-4 days and more than 70% of women have a mean segment length which is no less than 23 days and no greater than 32 days. The lowest median range of segment lengths (7 days) occurs at age 38 (Figure 7). In virtually all age groups, however, 25% of women have a range of at least 19 days, and 5% have a range of 50 days or more. The minimum segment length changes little with
Menstrual Bleeding Patterns
Contraception 1997;55:57-65
-
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Belsey et al.
Contraception 1997:55:57-65
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Figure 6. Mean length of segments (percentiles).
age. Three-quarters of women aged 15-44 have no segment shorter than 19 days, although a small proportion (approximately 5%) have a segment lasting only G-7 days (data not shown). The median value of the maximum segment falls from 41 days at age 15 years to 30 days at age 41, and then increases to 47 days at age 49. In the age range 20-41 years, one-quarter of women have at least one segment which exceeds 35 days, and 5% have a maximum segment length of 77 days or more. Table 1 shows, for 5-year age groups, the proportions of women who have a ‘normal’ bleeding pattern, or amenorrhea, infrequent, frequent, irregular, or prolonged bleeding in each of the four 90-day reference periods in a year. Differences between the reference periods within each age group are minimal, indicating that there is little seasonal variation in bleeding patterns. The proportion of women with a ‘normal’ pattern increases from approximately 70% in the group aged 15-19 years to a maximum of 92% in the group aged 35-39, and then falls to 75% among women aged 45-49. Amenorrhea is rare in all age groups, but particularly among women aged 25-39, where the incidence is less than 1%. The incidence of infrequent bleeding decreases from 20% in 15-19 year-olds to 5% among women aged 3539 and then rises to 17% among those aged 45 or over. Frequent bleeding (more
than 5 episodes in 90 days) is almost unknown, and was experienced by only one woman in each of the first and fourth reference periods, two women in the second, and none in the third. The proportion of women with irregular bleeding is 3% overall, falling from 6% of teenagers to l-2% of women aged 40 or over. This is the only bleeding pattern disturbance the incidence of which continues to decrease after age 39. Prolonged bleeding (an episode lasting 14 days or more) is almost as rare as frequent bleeding: it was recorded by five women in each of the first and fourth reference periods [of whom two, in each case, were aged 45-49), three women in the second period [of whom one was aged 45-49), and one (aged 45-49) in the third.
Discussion Treloar and co-workers set out to disprove the myth that women menstruate regularly, at 28-day intervals. Our aim was to describe menstrual patterns among healthy women unaffected by pregnancy, lactation, or contraception, so as to provide baseline data with which to compare the bleeding patterns observed among women using hormonal methods of contraception such as oral pills, injectables, vaginal rings, and implants, and those using intrauterine devices. These
1
Menstrual Bleeding Patterns
Contraception 19975557-65
I
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25
27
29
31
33
35
37
39
41
43
45
47
.
49
Age (Yea@
Figure
7. Range of lengths of segments over one year (percentiles).
differing purposes have affected the methodology employed. Treloar’s group included in their analyses all segments recorded, whether or not they were potentially affected by surgery, illness, or medication, for fear of excluding any unusually long or short events that were, in fact, unaffected by the state of health of the participant. They also included data recorded immediately following post-partum resumption of menstruation, when variability is high. We have excluded any calendar years in which menstrual disorders, hormone therapy, or gynecological surgery were recorded, or menstruation might have been affected by pregnancy or lactation. It is difficult to judge the likely effects of these differences in methodology on mean segment length, but our analyses would probably result in lower estimates of within-woman variability. On the other hand, we have defined the start of a segment as ‘any set of one or more bleeding/ spotting days’ and thus viewed intermenstrual bleeding as constituting the start of a new segment; Treloar and co-workers used notes provided by the participants to help distinguish between menstrual and intermenstrual bleeding and excluded the latter from consideration. From this point of view, our analyses could be expected to show increased numbers of shorter segments and greater within-woman variability. Unfortunately, it is impossible to compare
within-woman variability in the two sets of results, since Treloar and co-workers calculated the standard deviation of event lengths, whereas, following the WHO recommendation,2 we have used the range. However, the net effects on within-woman mean segment lengths are trivial: between the ages of 21 and 30 years, our analyses give a median value which is 0.3 to 1 .O days shorter than Treloar’s; between 35 and 39 years of age, our median values are 0.1 to 0.4 days greater. The analysis revealed extreme values in the distributions of some indices, particularly the ranges of bleeding-free interval and segment lengths. These values could simply result from women omitting to record one or more episodes, and then failing to note a break in record-!Tseping. Alternatively, since none of the women recruited to the study were screened or examined, and uI_ 011Lealth problems were self-reported, there can be no absolute certainty that they started in good health, or remained so throughout their participation. The data also need to be considered in their historical context. The introduction of radioimmunoassays in the late 1960s led to an explosion of knowledge and of diagnostic capabilities. Conditions such as the polycystic ovarian syndrome, hypothalamic disorders, hyperprolactinemia, or premature ovarian failure could be defined more accurately and at less
64
Table
Belsey et al
1. Proportion
Contraception 1997,55:57-65
I%) of women
with
each type of “clinically
important”
bleeding
pattern
Age (years) 15-19
20-24
25-29
30-34
35-39
40-44
45-49
All Ages
70.8 68.9 71.2 75.3
82.0 82.0 80.5 86.0
86.9 86.0 85.5 88.3
88.3 87.9 87.2 89.8
91.3 92.9 91.4 93.2
89.5 90.0 88.0 89.8
76.4 76.4 70.6 75.6
84.0 83.8 82.7 86.1
2.4 2.3 1.5 3.3
2.0 2.1 1.9 1.7
0.7 0.6 0.5 0.8
0.6 1.3 1.2 1.6
0.7 1.3
0.9 2.0 2.2 2.8
3.2 6.3 7.3 9.1
1.4 1.9 1.8 2.4
20.3 21.5 21.0 17.0
12.7 12.1 12.8 9.7
9.3 10.2 10.1 8.6
8.2 8.6 8.2 6.3
5.8 4.6 5.2 4.0
8.0 6.3 8.5 6.3
18.8 15.3 20.8 14.1
11.5 11.1 11.8 9.1
0.0 0.0 0.0 0.0
0.0 0.1 0.0 0.1
0.0 0.1 0.0 0.0
0.0 0.0 0.0 0.0
0.1 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
6.3 7.4 6.3 4.4
3.2 3.7 4.8 2.5
3.1 3.1 3.8 2.4
2.9 2.3 3.4 2.3
2.4 1.8 2.8 1.5
1.5 1.7 1.4 1.1
1.6 2.0 1.4 1.2
3.2 3.3 3.7 2.3
0.0 0.0 0.0 0.2
0.1 0.1 0.0 0.0
0.0 0.0 0.0 0.1
0.0 0.0 0.0 0.0
0.1 0.1 0.0 0.0
0.0 0.0 0.0 0.0
0.4 0.2 0.2 0.4
0.1 0.0 0.0 0.1
RP = Reference period. Percentages may sum to more than 100, since all women
with prolonged
Normal RP I RP II RP III RPIV Amenorrhea RP I RP II RPIII RP IV Infrequent bleeding RPI RP II RP III RPIV Frequent bleeding RPI RPII RP III RPIV Irregular bleeding RP I RP II RP III RP IV Prolonged bleeding RPI RP II RP III RPIV
bleeding
overt stages of clinical manifestation. Thus, the value of the clinical history provided by each woman is dependent on the decade when it was recorded. Some of the menstrual disturbances considered ‘normal’ in the 1930s would have been labeled pathological in the 1970s. Nevertheless, our findings support Treloar and coworkers’ assertion that women do not “normally vary in menstrual interval about a value of 28 days common to all. Each woman has her own central trend and variation,” and that “complete regularity in menstruation through extended time is a myth.” Even over a one-year period, only a very small minority of women had a zero value for their range of segment lengths. These results also refute the belief that the ‘normal’ cycle length is 2535 days: the 5th and 95th percentiles of the distributions of within-woman mean segment lengths are approximately 24 and 42 days, respectively. Our results also confirm Treloar’s conclusion that there are three “zones” of menstrual life. Between menarche and age 19 years, the dominant feature of
i:;
also had infrequent
bleeding
menstrual patterns is their variability, although segments also tend to be longer than later in life. Throughout the middle zone, mean segment length decreases slowly but steadily, from 29 days at age 20 to 27 days at age 41. The range of segment lengths also falls throughout this period, reaching a minimum of 7 days at age 38. During the 4Os, the range increases sharply, to 28 days at age 49, while the mean segment length also rises, less sharply, to 29 days. The length and variability of bleeding episodes, however, change imperceptibly over the 30 years between the ages of 19 and 49. The original participants in Treloar and co-workers’ study were women of Scandinavian origin, studying at the University of Minnesota in the mid-1930s. Later on, these women comprised only one-half of the participants while the remainder resided throughout the United States. Although the ethnicity of each participant
is not
known,
it is likely
that
the
majority
were Caucasian. This should be taken into account when using these results as a baseline for comparison, since it has been shown that a woman’s geographical
Menstrual Bleeding Patterns
Contraception 1997;55:57-65
region of residence is a significant factor in her menstrual experience,6f7 probably reflecting a combination of ethnic origin, nutritional status, and other factors. It is interesting to note, however, that this group of untreated women recorded more bleeding days than women using hormonal contraceptives such as combined oral pills, the levonorgestrel-releasing vaginal ring, monthly injectables, or the long-acting injectable, depot medroxyprogesterone acetate (DMPA).4J8 With the exception of DMPA and Norplant’“, which tend to cause irregular, prolonged episodes of bleeding or spotting and long bleeding-free intervals,4’9 most hormonal methods of contraception produce a mean segment length which is within 2 days of the ‘normal’ 28-day segment.” The main difference between untreated patterns and those produced by hormonal contraceptives lies in their variability, both withinwoman and between women. The median range of segment lengths over a year increases from 9-10 days in untreated women to 24 days among women using a monthly injectable or vaginal ring.” Finally, these results call into question the WHO definitions of infrequent bleeding (fewer than 3 bleeding episodes per 90-day period], frequent bleeding (more than 5 episodes per 90 days), and prolonged bleeding (an episode lasting 14 days or more). These definitions are intended to identify ‘clinically important’ or ‘unacceptable’ bleeding patterns, which would be outside most women’s experience. However, they were established by consensus, without the benefit of any data on ‘normal’ bleeding patterns. Based on these definitions, approximately 10% of women of all ages, and one-fifth of those aged 15-19 or 45-49, were categorized as having infrequent bleeding in at least one 90-day reference period in a calendar year. Infrequent bleeding would be better defined as ‘fewer than 2 episodes per 90-day period.’ This would be approximately equivalent to the 5th percentile value of the number of bleeding episodes at ages 20-40 years. In contrast, frequent bleeding and prolonged bleeding, as defined by WHO, were almost unknown in this normal population. In these cases, the definitions are clearly too extreme. Frequent bleeding should be re-defined as ‘more than 4 episodes in a 90-day period.’ A more useful definition of prolonged bleeding would be ‘an episode lasting 10 days or more’; this corresponds to the 95th percentile of the
distribution of maximum episode length over a 90day reference period from ages 20 to 40 years. Finally, the definition of irregular bleeding should be altered to ‘a range of lengths
of bleeding-free
intervals
exceed-
65
ing 17 days’; this corresponds to the 95th percentile of the distribution of the range, the bleeding pattern index which most closely reflects the predictability of bleeding.
Acknowledgments We are very grateful to the College of Nursing of the University of Utah, Salt Lake City, for access to the Tremin Trust dataset. Requests for the data on which the Figures are based may be addressed to Dr C. d’Arcangues, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, 1211 Geneva 27, Switzerland.
References 1. Treloar AE, Boynton RE, Behn BG, Brown BW. Variation of the human menstrual cycle through reproductive life. Int J Fertil 1967;12:77-126. 2. Belsey EM, Machin D, d’Arcangues C. The analysis of vaginal bleeding patterns induced by fertility regulating methods. Contraception 1986;34:253-60. 3. Rodriguez G, Faundes-Latham A, Atkinson LE. An approach to the analysis of menstrual patterns in the critical evaluation of contraceptives. Stud Fam Plann 1976; 7:42-5 1. 4. Belsey EM, Task Force on Long-Acting Systemic Agents for Fertility Regulation. Vaginal bleeding patterns among women using one natural and eight hormonal methods of contraception. Contraception 1988; 38:181-206. 5. Belsey EM, Task Force on Long-Acting Systemic Agents for Fertility Regulation. The association between vaginal bleeding patterns and reasons for discontinuation of contraceptive use. Contraception 1988;38: 207-25. 6. Belsey EM, Peregoudov S, Task Force on Long-Acting Systemic Agents for Fertility Regulation. Determinants of menstrual bleeding patterns among women using natural and hormonal methods of contraception. I. Regional variations. Contraception 1988;38:227-42. 7. Snowden R, Christian B, eds. Patterns and perceptions of menstruation. London: Croom Helm, 1983. 8. World Health Organization Special Programme of Research, Development and Research Training in Human Reproduction, Task Force on Long-Acting Systemic Agents for Fertility Regulation. A multicentred Phase III comparative study of two hormonal contraceptive preparations given once-a-month by intramuscular injection. II. The comparison of bleeding patterns. Contraception 1989;40:53 l-5 1. 9. Sivin I, Sanchez FA, Diaz S, et al. Three-year experience with NorplantTM subdermal contraception. Fertil Steril 1983;39:799-808. 10. Belsey EM, Task Force on Long-Acting Systemic Agents for Fertility Regulation. Menstrual bleeding patterns in untreated women and with long-acting methods of contraception. Adv Contracept 1991;7:257-70.
Menstrual Untreated Elizabeth M. Belsey,t* Fertility Regulation?
Bleeding Patterns in Women Alain P.Y. Pinol,t and Task Force on Long-Acting
Menstrual histories recorded by more than 1000 healthy, untreated women have been analyzed using the reference period method. Results were obtained for each year of age from 15 to 49. Between menarche and age 19, the most important feature of menstrual patterns is their variability. Within-woman mean segment (cycle) length then decreasesslowly but steadily, from 29.0 days at age20 to 26.7 days at age 40. The range of segment lengths over a year also falls, to a minimum of 7 days at age 38. During the 40s mean segment length rises to 29 days at age 49, and there is a sharp increasein the range, to 28 days. The length and variability of bleeding episodes, however, changes little between the ages of 19 and 49. Modifications to the World Health Organization definitions of ‘clinically important’ bleeding patterns are proposed. 0 1997 Elsevier Science Inc. All rights reserved. CONTRACEPTION 1997;55:57-65
menstrual bleeding patterns, clinically tant patterns, reference period analysis
KEY WORDS:
impor-
Introduction uring the 19305 Dr Alan Treloar and his coworkers at the University of Minnesota started to collect information which would enable them to describe the length and variability of the menstrual cycle. Female students entering the University between 1935 and 1938 were asked to complete a calendar-year record showing the beginning and ending date of each menstrual period. At the end of the year, the completed records were collected, and the participants were issued with a new record card for the following year. When they had completed their studies, contact with the women was main-
D
TSpecial Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, 1211 Geneva 27, Switzerland Name and address for correspondence: Dr. C. d’Arcangues, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organizatron, 1211 Geneva 27, Switzerland. Tel: (41 22) 791 21 11; Fax: (41 22) 7914171 Submitted for publication August 30, 1996 Revised November 13. 1996 Accepted for publication November 13, 1996 ‘Present address: SigmaPlus, 10 rue de la Rigolette, 1266 Duillier, Switzerland
0 1997 Elsevier Science Inc. All rights reserved, 655 Avenue of the Americas, New York, NY 10010
Systemic Agents for
tained annually by mail. Data collection continued for over 40 years; in time, some of the original participants’ daughters, other female relatives, and family friends were also enrolled in the study, as they reached menarche. Some of the results from the study were published in 1967.l At that time, the dataset included information on more than 275,000 menstrual cycles, recorded by 2700 women over a total of 25,800 years. Because of its size, the lengths of some of the menstrual histories, and the fact that participants in the study were normally menstruating women, the dataset is unique. The World Health Organization (WHO) Task Force on Long-Acting Systemic Agents for Fertility Regulation therefore requested, and obtained, a copy of part of the dataset from the Tremin Trust at the College of Nursing, University of Utah, where it is now housed. The objective of the analyses reported below was to describe bleeding patterns in ‘normal,’ untreated women, using the techniques of analysis recommended by WHO,2 so as to provide baseline data with which the patterns observed in women using hormonal or mechanical methods of contraception could be compared.
Methods The Dataset The dataset originally consisted of a series of chronological event codes with corresponding dates. The majority of these events were menstrual (either the start or end of menses). Other events coded included menarche, marriage, births, hormone therapy, gynecological surgery, and menstrual disorders. Breaks in recording were also noted. The dataset made available to WHO included records kept by 1109 women. Fifty-nine of these were excluded from analysis because their date of birth was unknown. The menstrual event codes and dates were then converted into a menstrual diary for each remaining woman, and the diaries were divided into calendar years. In total, there were records for all or part of 16,803 woman-years. Of these, 10,428 years or ISSN OOlO-7624/97/$17.00 PI I SO01 O-7624(96)00273-9
58
Belsey et al
part-years were excluded from analysis: 5269 were incomplete (due to menarche, menopause, or, more usually, a break in record-keeping); 1761 included some part or all of a pregnancy, and another 717 followed a year in which a pregnancy ended and thus could have included a period of post-partum amenorrhea or lactation (which were not included in the coded events); hormone therapy, gynecological surgery (dilatation and curettage or hysterectomy) or menstrual disorders were recorded in 1034; in 1115 there were obvious errors in recording (for example, two consecutive dates of onset of menses with no intervening date of end of menses); and 532 were recorded by girls aged less than 15 or women aged 50 or over. This left 6375 complete years in healthy, normally menstruating women of reproductive age.
Description of Menstrual Bleeding Patterns The reference period method3 was used to analyze the menstrual diary records. Days within a menstrual event were defined as bleeding days, and days outside menstrual events were defined as bleeding-free days. A bleeding episode was defined as any set of one or more bleeding days (either consecutive or separated by only one bleeding-free day) bounded at each end by two or more bleeding-free days. A bleeding-free interval was defined as any set of two or more consecutive bleeding-free days bounded by bleeding days. (Thus, a single bleeding-free day was treated as part of the bleeding episode surrounding it, in accordance with Treloar and co-workers’ own definitions’ and with previous reports of bleeding patterns in contracepting women.4-6) A bleeding segment was defined as the sum of a bleeding episode and the immediately following bleeding-free interval. Calendar-year reference periods were used for the majority of analyses. Each bleeding event (episode, interval, or segment) was assigned to the year in which it started, even if it ended in the subsequent year. The following bleeding pattern indices were calculated for each woman-year: the numbers of bleeding days and bleeding episodes begun, and the mean, range, minimum, and maximum values of bleeding episode, bleeding-free interval, and segment lengths. The range of episode (or interval/segment) lengths, defined as the difference between the longest and the shortest, could only be calculated if at least two episodes (or intervals/segments) started during the year. The numbers of bleeding days and episodes were then multiplied by 90/365 so that they relate to a 90-day reference period. Additionally, the first 360 days in each year were divided into four 90-day reference periods, and the same indices were calculated for each period. The pe-
Contraception 19973557-65
riods were then divided into six subgroups, according to which of the following ‘clinically important’ bleeding patterns (as defined by WH02) had occurred: 1. Amenorrhea: no bleeding during the reference period 2. Infrequent bleeding: fewer than 3 bleeding episodes 3. Frequent bleeding: more than 5 bleeding episodes 4. Irregular bleeding: between 3 and 5 episodes with less than 3 bleeding-free intervals of length 14 days or more 5. Prolonged bleeding: 1 or more bleeding episodes lasting 14 days or more 6. None of the above: a ‘normal’ bleeding pattern. Statistical Methods Each woman-year was classified according to the age of the woman attained during that year. For each single-year age group, the bleeding pattern indices were summarized by calculating the median, and the 5th, 25th, 75th, and 95th percentiles.
Results Between 190 and 299 calendar-year diaries were available for analysis for each single year of age from 19 to 36 years. The minimum number of diaries included in analysis, at age 49 years, was 89. The number of bleeding days recorded over 90 days, according to the age of the woman, is shown in Figure 1. The median value is 19 days for all but one of the single-year age groups between 15 and 34, increases to 20 days between the ages of 35 and 45 years, and then falls to 18 days by age 48. In the age range 20-34 years, at most, 10% of women have less than 11 or more than 26 bleeding days per 90&y period. The variability between women increases thereafter, particularly at the lower end of the distribution, and at age 49, 25% of women have less than 10 bleeding days in every 90. The median number of bleeding episodes increases from 2.7 per 90 days at age 15 years to 3.2 at age 21, remains constant over the next two decades of reproductive life, increases again to 3.4 at age 40, and finally falls, from age 46 onward, to 2.9 at age 49 (Figure 2). There is very little variation between women, even at the lower and upper ends of the age range. Between the ages of 22 and 41 years, 90% of women have no fewer than 2.0 and no more than 3.6 episodes every 90 days. The median value of the mean length of bleeding episodes starts at 6.6 days at 15 years of age, and falls to 6.0 days by age 21 where, with minor variations, it remains unchanged until age 49 (Figure 3). Less than
Contraception 1997;55:5745
Menstrual Bleeding Patterns
59
----95th‘-.--..75t,, -50th ---
25th
~----5th
0
r1-,
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17
19
21
23
26
27
29
31
33
Age
Figure
3.6
1. Number
1
/
.
of bleeding
days per 90-day period
/‘\ ‘\ .,' _-. ,' -.
‘\./'
1' 3.2 A
,'
*-.
37
39
41
43
46
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(years)
(percentiles).
*/-..
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'.
/ .,'
,__.._____.____..___......--..~~..... - ,-
, /
, -2.6 4 '
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.__--
2.4 1 ~ I
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.
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~~ - - - - 95th i-----.75th
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0 A16
----7 17
19
21
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Figure 2. Number
of bleeding
episodes
per 90-day period
---33
35
(YeaW
(percentiles).
-, 37
39
,7 41
43
45
47
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~---
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i
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,-
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60
Belsey et al.
Contraception 199755~57-65
3.5 15
17
19
21
23
25
27
29
31 Age
Figure
33
35
37
39
41
43
45
47
49
(Yea@
3. Mean length of bleeding episodes[percentiles).
5% of women have bleeding episodes the average length of which are less than 4 days; at the other end of the spectrum, only 5% have episodes with an average length of 8 days or more. Within-woman, episodes vary little in length. At least 25% and, in some single-year age groups, more than 50% of women, have episodes which differ in length by only 1 day over a year (data not shown). At ages 15-43 years, three-quarters of women have no more than a &day variation in the lengths of their episodes. Variability increases slightly after age 44 but even then, 75% of women have only a 4-5 day difference between their shortest and longest episodes. At least 95 % of women of all ages have a minimum episode length of 3 days, while the maximum length has a median value of 7-8 days, an upper quartile of 8-10 days, and a 95th percentile of 9-12 days until age 40 and 12-17 days thereafter (data not shown). Figure 4 shows the within-woman mean length of bleeding-free intervals. The median value decreases steadily from 25 days at age 15 years to a minimum of 20 days at age 41, and then increases to 23 days at age 49. At all ages, at least 5% of women have intervals with an average length of only 17-18 days. At age 15 years, the median value of the range of bleeding-free interval
lengths is 18 days, and 25% of
girls have intervals which vary by 34 days or more (Figure 5). Variability in the lengths of bleeding-free intervals then decreases, and is at its lowest in the age range 23-41 years. Even in these middle years, however, one-half of women have a range of 7 days or more, and 25% have one of at least 13 days. In the pre-menopausal years, variability increases again, and at age 49,50% of women have bleeding-free intervals which differ by at least 28 days, and 5% have a range of approximately 6 months. Figure 6 shows the distributions of the withinwoman mean segment length for each year of age. The changes with increasing age follow the same pattern as the mean bleeding-free interval: the median value falls from 32 days at age 15 years to 27 days at age 41, and then rises to 29 days at age 49. Although there are some extreme values in each single-year age group, there is, in general, relatively little variation between women. Between the ages of 21 and 41 years, the interquartile range is only 3-4 days and more than 70% of women have a mean segment length which is no less than 23 days and no greater than 32 days. The lowest median range of segment lengths (7 days) occurs at age 38 (Figure 7). In virtually all age groups, however, 25% of women have a range of at least 19 days, and 5% have a range of 50 days or more. The minimum segment length changes little with
Menstrual Bleeding Patterns
Contraception 1997;55:57-65
-
60/-
I
50
46
30
10
/?-
15
17
19
21
23
25
29
27
31 Age
Figure
4. Mean
length
of bleeding-free
-4----___ -w-_----m_-
19
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21
5. Range of lengths
23
intervals
of bleeding-free
27
35
37
39
41
43
45
47
49
(yea@
(percentiles).
e------_-s ____._--
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33
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.__.
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over one year (percentiles).
39
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61
62
Belsey et al.
Contraception 1997:55:57-65
r
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Figure 6. Mean length of segments (percentiles).
age. Three-quarters of women aged 15-44 have no segment shorter than 19 days, although a small proportion (approximately 5%) have a segment lasting only G-7 days (data not shown). The median value of the maximum segment falls from 41 days at age 15 years to 30 days at age 41, and then increases to 47 days at age 49. In the age range 20-41 years, one-quarter of women have at least one segment which exceeds 35 days, and 5% have a maximum segment length of 77 days or more. Table 1 shows, for 5-year age groups, the proportions of women who have a ‘normal’ bleeding pattern, or amenorrhea, infrequent, frequent, irregular, or prolonged bleeding in each of the four 90-day reference periods in a year. Differences between the reference periods within each age group are minimal, indicating that there is little seasonal variation in bleeding patterns. The proportion of women with a ‘normal’ pattern increases from approximately 70% in the group aged 15-19 years to a maximum of 92% in the group aged 35-39, and then falls to 75% among women aged 45-49. Amenorrhea is rare in all age groups, but particularly among women aged 25-39, where the incidence is less than 1%. The incidence of infrequent bleeding decreases from 20% in 15-19 year-olds to 5% among women aged 3539 and then rises to 17% among those aged 45 or over. Frequent bleeding (more
than 5 episodes in 90 days) is almost unknown, and was experienced by only one woman in each of the first and fourth reference periods, two women in the second, and none in the third. The proportion of women with irregular bleeding is 3% overall, falling from 6% of teenagers to l-2% of women aged 40 or over. This is the only bleeding pattern disturbance the incidence of which continues to decrease after age 39. Prolonged bleeding (an episode lasting 14 days or more) is almost as rare as frequent bleeding: it was recorded by five women in each of the first and fourth reference periods [of whom two, in each case, were aged 45-49), three women in the second period [of whom one was aged 45-49), and one (aged 45-49) in the third.
Discussion Treloar and co-workers set out to disprove the myth that women menstruate regularly, at 28-day intervals. Our aim was to describe menstrual patterns among healthy women unaffected by pregnancy, lactation, or contraception, so as to provide baseline data with which to compare the bleeding patterns observed among women using hormonal methods of contraception such as oral pills, injectables, vaginal rings, and implants, and those using intrauterine devices. These
1
Menstrual Bleeding Patterns
Contraception 19975557-65
I
15or 135
120
i
b-
I
I
i
I--
Ii
l
>
\
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k
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63
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19
21
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25
27
29
31
33
35
37
39
41
43
45
47
.
49
Age (Yea@
Figure
7. Range of lengths of segments over one year (percentiles).
differing purposes have affected the methodology employed. Treloar’s group included in their analyses all segments recorded, whether or not they were potentially affected by surgery, illness, or medication, for fear of excluding any unusually long or short events that were, in fact, unaffected by the state of health of the participant. They also included data recorded immediately following post-partum resumption of menstruation, when variability is high. We have excluded any calendar years in which menstrual disorders, hormone therapy, or gynecological surgery were recorded, or menstruation might have been affected by pregnancy or lactation. It is difficult to judge the likely effects of these differences in methodology on mean segment length, but our analyses would probably result in lower estimates of within-woman variability. On the other hand, we have defined the start of a segment as ‘any set of one or more bleeding/ spotting days’ and thus viewed intermenstrual bleeding as constituting the start of a new segment; Treloar and co-workers used notes provided by the participants to help distinguish between menstrual and intermenstrual bleeding and excluded the latter from consideration. From this point of view, our analyses could be expected to show increased numbers of shorter segments and greater within-woman variability. Unfortunately, it is impossible to compare
within-woman variability in the two sets of results, since Treloar and co-workers calculated the standard deviation of event lengths, whereas, following the WHO recommendation,2 we have used the range. However, the net effects on within-woman mean segment lengths are trivial: between the ages of 21 and 30 years, our analyses give a median value which is 0.3 to 1 .O days shorter than Treloar’s; between 35 and 39 years of age, our median values are 0.1 to 0.4 days greater. The analysis revealed extreme values in the distributions of some indices, particularly the ranges of bleeding-free interval and segment lengths. These values could simply result from women omitting to record one or more episodes, and then failing to note a break in record-!Tseping. Alternatively, since none of the women recruited to the study were screened or examined, and uI_ 011Lealth problems were self-reported, there can be no absolute certainty that they started in good health, or remained so throughout their participation. The data also need to be considered in their historical context. The introduction of radioimmunoassays in the late 1960s led to an explosion of knowledge and of diagnostic capabilities. Conditions such as the polycystic ovarian syndrome, hypothalamic disorders, hyperprolactinemia, or premature ovarian failure could be defined more accurately and at less
64
Table
Belsey et al
1. Proportion
Contraception 1997,55:57-65
I%) of women
with
each type of “clinically
important”
bleeding
pattern
Age (years) 15-19
20-24
25-29
30-34
35-39
40-44
45-49
All Ages
70.8 68.9 71.2 75.3
82.0 82.0 80.5 86.0
86.9 86.0 85.5 88.3
88.3 87.9 87.2 89.8
91.3 92.9 91.4 93.2
89.5 90.0 88.0 89.8
76.4 76.4 70.6 75.6
84.0 83.8 82.7 86.1
2.4 2.3 1.5 3.3
2.0 2.1 1.9 1.7
0.7 0.6 0.5 0.8
0.6 1.3 1.2 1.6
0.7 1.3
0.9 2.0 2.2 2.8
3.2 6.3 7.3 9.1
1.4 1.9 1.8 2.4
20.3 21.5 21.0 17.0
12.7 12.1 12.8 9.7
9.3 10.2 10.1 8.6
8.2 8.6 8.2 6.3
5.8 4.6 5.2 4.0
8.0 6.3 8.5 6.3
18.8 15.3 20.8 14.1
11.5 11.1 11.8 9.1
0.0 0.0 0.0 0.0
0.0 0.1 0.0 0.1
0.0 0.1 0.0 0.0
0.0 0.0 0.0 0.0
0.1 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
6.3 7.4 6.3 4.4
3.2 3.7 4.8 2.5
3.1 3.1 3.8 2.4
2.9 2.3 3.4 2.3
2.4 1.8 2.8 1.5
1.5 1.7 1.4 1.1
1.6 2.0 1.4 1.2
3.2 3.3 3.7 2.3
0.0 0.0 0.0 0.2
0.1 0.1 0.0 0.0
0.0 0.0 0.0 0.1
0.0 0.0 0.0 0.0
0.1 0.1 0.0 0.0
0.0 0.0 0.0 0.0
0.4 0.2 0.2 0.4
0.1 0.0 0.0 0.1
RP = Reference period. Percentages may sum to more than 100, since all women
with prolonged
Normal RP I RP II RP III RPIV Amenorrhea RP I RP II RPIII RP IV Infrequent bleeding RPI RP II RP III RPIV Frequent bleeding RPI RPII RP III RPIV Irregular bleeding RP I RP II RP III RP IV Prolonged bleeding RPI RP II RP III RPIV
bleeding
overt stages of clinical manifestation. Thus, the value of the clinical history provided by each woman is dependent on the decade when it was recorded. Some of the menstrual disturbances considered ‘normal’ in the 1930s would have been labeled pathological in the 1970s. Nevertheless, our findings support Treloar and coworkers’ assertion that women do not “normally vary in menstrual interval about a value of 28 days common to all. Each woman has her own central trend and variation,” and that “complete regularity in menstruation through extended time is a myth.” Even over a one-year period, only a very small minority of women had a zero value for their range of segment lengths. These results also refute the belief that the ‘normal’ cycle length is 2535 days: the 5th and 95th percentiles of the distributions of within-woman mean segment lengths are approximately 24 and 42 days, respectively. Our results also confirm Treloar’s conclusion that there are three “zones” of menstrual life. Between menarche and age 19 years, the dominant feature of
i:;
also had infrequent
bleeding
menstrual patterns is their variability, although segments also tend to be longer than later in life. Throughout the middle zone, mean segment length decreases slowly but steadily, from 29 days at age 20 to 27 days at age 41. The range of segment lengths also falls throughout this period, reaching a minimum of 7 days at age 38. During the 4Os, the range increases sharply, to 28 days at age 49, while the mean segment length also rises, less sharply, to 29 days. The length and variability of bleeding episodes, however, change imperceptibly over the 30 years between the ages of 19 and 49. The original participants in Treloar and co-workers’ study were women of Scandinavian origin, studying at the University of Minnesota in the mid-1930s. Later on, these women comprised only one-half of the participants while the remainder resided throughout the United States. Although the ethnicity of each participant
is not
known,
it is likely
that
the
majority
were Caucasian. This should be taken into account when using these results as a baseline for comparison, since it has been shown that a woman’s geographical
Menstrual Bleeding Patterns
Contraception 1997;55:57-65
region of residence is a significant factor in her menstrual experience,6f7 probably reflecting a combination of ethnic origin, nutritional status, and other factors. It is interesting to note, however, that this group of untreated women recorded more bleeding days than women using hormonal contraceptives such as combined oral pills, the levonorgestrel-releasing vaginal ring, monthly injectables, or the long-acting injectable, depot medroxyprogesterone acetate (DMPA).4J8 With the exception of DMPA and Norplant’“, which tend to cause irregular, prolonged episodes of bleeding or spotting and long bleeding-free intervals,4’9 most hormonal methods of contraception produce a mean segment length which is within 2 days of the ‘normal’ 28-day segment.” The main difference between untreated patterns and those produced by hormonal contraceptives lies in their variability, both withinwoman and between women. The median range of segment lengths over a year increases from 9-10 days in untreated women to 24 days among women using a monthly injectable or vaginal ring.” Finally, these results call into question the WHO definitions of infrequent bleeding (fewer than 3 bleeding episodes per 90-day period], frequent bleeding (more than 5 episodes per 90 days), and prolonged bleeding (an episode lasting 14 days or more). These definitions are intended to identify ‘clinically important’ or ‘unacceptable’ bleeding patterns, which would be outside most women’s experience. However, they were established by consensus, without the benefit of any data on ‘normal’ bleeding patterns. Based on these definitions, approximately 10% of women of all ages, and one-fifth of those aged 15-19 or 45-49, were categorized as having infrequent bleeding in at least one 90-day reference period in a calendar year. Infrequent bleeding would be better defined as ‘fewer than 2 episodes per 90-day period.’ This would be approximately equivalent to the 5th percentile value of the number of bleeding episodes at ages 20-40 years. In contrast, frequent bleeding and prolonged bleeding, as defined by WHO, were almost unknown in this normal population. In these cases, the definitions are clearly too extreme. Frequent bleeding should be re-defined as ‘more than 4 episodes in a 90-day period.’ A more useful definition of prolonged bleeding would be ‘an episode lasting 10 days or more’; this corresponds to the 95th percentile of the
distribution of maximum episode length over a 90day reference period from ages 20 to 40 years. Finally, the definition of irregular bleeding should be altered to ‘a range of lengths
of bleeding-free
intervals
exceed-
65
ing 17 days’; this corresponds to the 95th percentile of the distribution of the range, the bleeding pattern index which most closely reflects the predictability of bleeding.
Acknowledgments We are very grateful to the College of Nursing of the University of Utah, Salt Lake City, for access to the Tremin Trust dataset. Requests for the data on which the Figures are based may be addressed to Dr C. d’Arcangues, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, 1211 Geneva 27, Switzerland.
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