ORIGINAL E n d o c r i n e ARTICLE R e s e a r c h Reproductive and Lifestyle Determinants of AntiMüllerian Hormone in a Large Population-based Study M. Dólleman, W. M. M. Verschuren, M. J. C. Eijkemans, M. E. T. Dollé, E. H. J. M. Jansen, F. J. M. Broekmans, and Y. T. van der Schouw Department of Reproductive Medicine and Gynaecology (M.D., F.J.M.B.); Julius Center for Health Sciences and Primary Care (M.D., M.J.C.E., Y.T.v.d.S.), University Medical Center Utrecht, 3508 GA Utrecht, The Netherlands; and National Institute for Public Health and the Environment (W.M.M.V., M.E.T.D., E.H.J.M.J.), 3720 BA Bilthoven, The Netherlands Context: Anti-müllerian hormone (AMH) is an ovarian reserve marker that is increasingly applied in clinical practice as a prognostic and diagnostic tool. Despite increased use of AMH in clinical practice, large-scale studies addressing the influence of possible determinants on AMH levels are scarce. Objective: We aimed to address the role of reproductive and lifestyle determinants of AMH in a large population-based cohort of women. Design: In this cross-sectional study, age-specific AMH percentiles were calculated using general linear modeling with CG-LMS (Cole and Green, Lambda, Mu, and Sigma model, an established method to calculate growth curves for children). Setting: Women from the general community participating in the Doetinchem Cohort study were assessed. Participants: Two thousand three hundred twenty premenopausal women were included. Main Outcome Measure: The effect of female reproductive and lifestyle factors on shifts in agespecific AMH percentiles was studied. Results: In comparison to women with a regular menstrual cycle, current oral contraceptive (OC) users, women with menstrual cycle irregularity, and pregnant women had significantly lower age-specific AMH percentiles (for OC use, 11 percentiles lower; for cycle irregularity, 11 percentiles lower; and for pregnancy, 17 percentiles lower [P value for all ⬍.0001]). Age at menarche and age at first childbirth were not associated with the age-specific AMH percentile. Higher parity was associated with 2 percentiles higher age-specific AMH (P ⫽ .02). Of the lifestyle factors investigated, current smoking was associated with 4 percentiles lower age-specific AMH percentiles (P ⫽ .02), irrespective of the smoking dose. Body mass index, waist circumference, alcohol consumption, physical exercise, and socioeconomic status were not significantly associated with age-specific AMH percentiles. Conclusions: This study demonstrates that several reproductive and lifestyle factors are associated with age-specific AMH levels. The lower AMH levels associated with OC use and smoking seem reversible, as effects were confined to current use of OC or cigarettes. It is important to give careful consideration to the effect of such determinants when interpreting AMH in a clinical setting and basing patient management on AMH. (J Clin Endocrinol Metab 98: 2106 –2115, 2013) ISSN Print 0021-972X ISSN Online 1945-7197 Printed in U.S.A. Copyright © 2013 by The Endocrine Society Received November 26, 2012. Accepted February 27, 2013. First Published Online March 26, 2013 2106 jcem.endojournals.org Abbreviations: AMH, anti-müllerian hormone; BMI, body mass index; CG-LMS model, Cole and Green Lambda Mu Sigma model; DCS, Doetinchem Cohort Study; OC, oral contraceptive; PCOS, polycystic ovary syndrome; SES, socioeconomic status. J Clin Endocrinol Metab, May 2013, 98(5):2106 –2115 doi: 10.1210/jc.2012-3995 doi: 10.1210/jc.2012-3995 nti-müllerian hormone (AMH) is a marker of female “ovarian reserve,” or the number of follicles remaining in a woman’s ovaries (1). AMH is increasingly used in clinical practice for both prognostic purposes, such as prediction of ovarian response during in vitro fertilization treatment, prediction of age at menopause, and diagnostic purposes, such as the identification of women with premature ovarian insufficiency or polycystic ovary syndrome (2– 6). Several studies have presented nomograms for clinical interpretation of AMH levels in different populations (7– 12). However, there are suggestions that AMH varies according to oral contraceptive (OC) use, smoking, and body mass index (BMI), casting doubt on the clinical utility of these nomograms (13–17). Although it is generally believed that smoking is deleterious to the ovarian reserve and AMH values (13, 18, 19), not all studies agree (8, 20) and most studies have not been designed to look at dose response and the influence of quitting smoking. Thus far, studies have remained inconclusive about the effect of other potential determinants, such as cycle regularity, current pregnancy, OC use, parity, age at menarche, age at first childbirth, BMI, waist circumference, alcohol consumption, physical exercise, or socioeconomic status (13–16, 21–24). These are factors that have been suggested to affect either female endocrinology, age at menarche, or age at menopause (25–27). The aim of this study is therefore to address the possible role of both reproductive and lifestyle determinants of AMH in a large cohort of women from the general population. A Materials and Methods Participants The Doetinchem Cohort Study (DCS) is an ongoing multipurpose prospective study, initially carried out in a random general population sample of men and women aged 20 to 59 years (1987–1991). Over 95% of the DCS population are Caucasian women (28). The aim of the DCS was to study the impact of (changes in) lifestyle factors and biological risk factors on various aspects of health, such as the incidence of chronic diseases, physical and cognitive functioning, and quality of life. The cohort is re-examined every 5 years with questionnaires and a physical examination at the local health service. Three follow-up examination rounds were completed during 1993–1997, 1998 – 2002, and 2003–2007. All participants gave written informed consent, and the study was approved according to the guidelines of the Helsinki Declaration by the Medical Ethics Committee of the Netherlands Organization of Applied Scientific Research. Details on the DCS have been extensively described elsewhere (29). For the present study we used a cross-sectional design among women participating in the second examination round of the jcem.endojournals.org 2107 DCS. Women were excluded from the current study if they were postmenopausal (n ⫽ 1700), if they were taking hormone replacement therapy (n ⫽ 23), if they had a history of surgery to the uterus or ovaries (n ⫽ 26), or if the information on their reproductive status was missing (n ⫽ 59). After exclusion, 2 320 from the original 4 128 women remained eligible for the current study. Potential AMH determinants The reproductive determinants included were age at menarche, OC use, cycle regularity status, pregnancy, parity, and age at first childbirth. The lifestyle determinants encompassed BMI, waist circumference, smoking, alcohol consumption, physical exercise, and socioeconomic status. Reproductive history was assessed via extensive questionnaires. Women were asked at what age they had their first menstrual period, if their period was regular, how long their menstrual cycle was in number of days, and how many menstruations they had in the last 12 months. Furthermore women were asked whether they were currently pregnant, if they had ever been pregnant, if so, how many pregnancies and how many children they had, as well as when the children were born. In addition, women were asked if they had ever used OC or hormone replacement therapy, how old they were when they started using this medication, if they were using it at the time of blood sampling for AMH measurements, and how many years they had used it in total. It was also inventoried whether and at what age women had undergone a hysterectomy and/or if they had ever been operated on one or both ovaries and at what age that occurred. A regular cycle was defined as having a regular cycle with a mean cycle length of 24 to 36 days. OC use was categorized as previous OC use, current OC use, and never used OC. The number of years of OC use was divided into ⬍1, 1–5, 5–10, 10 –15, 15–20, and ⬎ 20 years. Reproductive status at time of blood sampling was categorized into mutually exclusive categories of regularly cycling, irregularly cycling, currently pregnant, or currently taking OC. Parity was assessed as a continuous variable. Body weight and height were measured by trained staff. Body weight was measured to the nearest 100 g on calibrated scales with participants wearing light indoor clothing without shoes, with emptied pockets (29). BMI was categorized as normal (⬍25 kg/m2), overweight (25–30 kg/m2), and obese (ⱖ30 kg/m2). Waist circumference was measured to the nearest 0.5 cm according to World Health Organization instructions and categorized into normal (⬍80 cm), moderately increased (80 – 88 cm), and abdominal obesity (⬎88 cm) (30). Ever smokers were identified based on the question “did you ever smoke regularly.” For ever smokers, information on age at which the respondent started smoking, as well as the total number of years of smoking and average number of cigarettes smoked, was assessed, followed by a question on current smoking (“do you smoke at present”). Smoking was categorized as current smoker, ex-smoker, and never smoker. The amount of smoking was categorized into the following 5 levels: ⬍1 cigarette per month, ⬍1 cigarette per day, 1–9 cigarettes per day, 10 –19 cigarettes per day, and ⬎20 cigarettes per day. Pack-years of smoking was divided into 7 strata with 5-year intervals. Alcohol intake was assessed in the questionnaire as number of glasses consumed per week, and subsequently operationalized as number of beverages consumed daily. Physical activity was assessed using the validated (31) European Prospective Investigation into Cancer and Nutrition questionnaire and categorized according to the Cambridge Physical 2108 Dólleman et al Determinants of AMH J Clin Endocrinol Metab, May 2013, 98(5):2106 –2115 linear regression and the extent of smoothing can be modified by altering the degrees of freedom (33). The fitted model was used to predict the age-specific percentile of AMH of each woman in the database. Data were analyzed with SPSS version 20.0 (SPSS Inc, Chicago, Illinois) and with R version 2.13 (http://www.r-project.org/). The “gamlss” package, which is a collection of functions to fit Generalized Additive Models for Location Scale and Shape, was used to perform the CG-LMS method in R (www.gamlss.org) (34). Determinants of AMH Figure 1. Flowchart of included women. Activity Index into (moderately) active and (moderately) inactive (32). Socioeconomic status (SES) was classified into 4 categories according to the highest level of education that a woman had reached: primary school (SES level 1), lower secondary or vocational school (SES level 2), intermediate vocational or higher secondary school (SES level 3), and higher vocational or university (SES level 4) (29). AMH assay Blood samples were collected on a random day of the menstrual or OC cycle. Serum was frozen on the day of vena cubiti puncture and stored in liquid nitrogen. Before the AMH measurement, each sample went through one thaw-freeze cycle on ice for 4 hours; intermitted storage of samples until AMH measurement was at ⫺80°C for a maximum of 4 weeks. Serum AMH was measured with the AMH Gen II ELISA (Beckman-Coulter, Sinsheim, Germany) in a single laboratory, by the same experienced laboratory technician. The precision of assay results was validated with linearity-of-dilution assessment. The limit of detection for this assay is 0.08 ng/mL, and the limit of quantification is 0.16 ng/mL. The interassay and intra-assay coefficients of variation were 3.35% and 4.0%, respectively. Statistical analysis Baseline characteristics were described for the group as a whole with mean values and corresponding standard deviation for continuous variables and frequencies and percentages for categorical data. Age-specific reference values of AMH We age-standardized the distribution of AMH using the CGLMS method. This CG-LMS method, originally described by Cole and Green, is an established method to estimate growth curves for children. The LMS method summarizes the distribution of age-specific AMH by 3 smoothing splines, which represent the skewness (L), the median (M), and the coefficient of variation (S). These 3 splines are simultaneously fitted by non- The relationships between potential determinants and age-specific AMH percentiles were assessed in the cohort using univariable and multivariable regression analysis. Determinants were investigated for both linear and nonlinear associations with AMH by categorizing determinants into the clinically relevant categories as described above. The magnitude of the effect of the determinants was calculated as the number of percentiles of change. As percentiles of agestandardized AMH were used, no further correction for age in a multivariable analysis was needed. The change in percentiles is displayed with the standard error and the corresponding P value. Individual P values for categorical values in comparison to the reference value were calculated and the overall P value was measured with ANOVA between groups (p-ANOVA). For reproductive status at time of blood sampling, regularly cycling women were chosen as the reference category for the 3 other mutually exclusive categories of women. A P value of ⱕ.05 was considered to be statistically significant. The effect can thus be interpreted for dichotomous variables as “in the presence of determinant x, age-specific AMH is y percentiles lower/higher” and for continuous variables as “with a one unit higher level of determinant x, the AMH level is y percentiles higher/lower.” Results The study cohort comprised 2 320 women, as depicted in the flowchart in Figure 1, of whom 1 090 were regularly cycling, 908 were taking OC for family planning purposes, 49 were pregnant, and 273 had an irregular unpredictable cycle. The baseline characteristics of the cohort are shown in Table 1. Age-specific percentiles of AMH as estimated using the CG-LMS model are depicted in Supplemental Figure 1, published on The Endocrine Society’s Journals Online web site at http://jcem.endojournals.org. Reproductive determinants There was no association between age at menarche and AMH ( ⫽ .7, P ⫽ .09). In comparison to women with a regular menstrual cycle, current OC use, current pregnancy, and having an irregular menstrual cycle were all reproductive factors that were associated with having significantly lower age-specific AMH (Table 2). Current OC doi: 10.1210/jc.2012-3995 jcem.endojournals.org Table 1. Baseline Characteristics of the Cohort Mean (SD) or % (n) Lifestyle factors Age, y BMI Waist circumference Smoking Current smokers, % Ex-smokers, % Never smoked, % Number of cigarettes packs per day among smokers Number of pack years among smokers Alcohol Drink alcohol daily, % Amount of alcoholic beverages per day among drinkers Physical activity CPAI 1 (inactive) CPAI 2 (moderately inactive) CPAI 3 (moderately active) CPAI 4 (active) Socioeconomic status SES 1 SES 2 SES 3 SES 4 Reproductive factors Age at menarche Ever taken oral contraceptives Parity Age at birth of first child Reproductive status at AMH measurement Regularly cycle Irregular cycle Oral contraceptives Pregnant 2109 Table 2. Number of Percentiles that AMH Shifts in the Presence of a Specific Reproductive Determinant Linear Regression 37.3 (9.2) 24.3 (3.9) 84.6 (10.6) Determinants Percentiles of Change Standard Error P Value Reference ⫺11.0 ⫺11.0 ⫺16.6 2.2 1.3 4.1 ⬍.0001 ⬍.0001 ⬍.0001 Reference ⫺0.3 ⫺9.0 2.3 2.3 .88 ⬍.0001 Reference 2.6 ⫺2.2 ⫺2.6 ⫺3.9 ⫺8.8 0.7 2.1 ⫺0.2 3.1 3.0 3.2 3.5 4.2 0.4 0.9 0.2 .39 .46 .42 .26 .04 .09 .02 .39 5.2% (120) 47.4% (1099) 31.7% (736) 15.3% (356) Current reproductive status Regular cycle Irregular cycle Current OC use Current pregnancy History of OC use Never Previous Current Years of OC use in current or past users (n ⫽ 1996) ⬍1 y 1–5 y 5–10 y 10 –15 y 15–20 y ⬎20 y Age at menarche Parity Age at birth of first child 13.2 (1.4) 90.6% (2102) 2.1 (0.8) 25.4 (4.0) The association between reproductive determinants and age-specific AMH is quantified as the number of percentiles that AMH shifts in the presence of a specific determinant. Corresponding standard error and P value are shown. 47% (1090) 11.8% (273) 39.1% (908) 2.1% (49) Having given birth to a higher number of children was associated with higher age-specific AMH levels (per additional child,  ⫽ 2.1, P ⫽ .02). There was no association between the age at first childbirth and AMH ( ⫽ ⫺.2, P ⫽ .39). Results are displayed in Table 2. 32.8% (760) 29.2% (678) 38% (882) 12.6 (7.5) 10.2 (9.1) 46% (1068) 1.1 (0.9) 2.8% (62) 22.4% (464) 31.8% (622) 43% (872) Abbreviations: CPAI, Cambridge Physical Activity Index; SES, socioeconomic status. Means and standard deviations (SD) are shown for continuous variables. Percentage and numbers are shown for categorical variables. users had an age-specific AMH of 11 percentiles lower than women with a regular cycle ( ⫽ 11; P ⬍ .0001). When the history of OC use was assessed in the entire cohort, current OC users had significantly lower AMH values than women who had never used OC ( ⫽ ⫺9; P value ⬍.0001) but previous OC use was not associated with lower AMH values ( ⫽ ⫺.3; P ⫽ .9). There was no clear dose-response relationship of duration of OC use with age-specific AMH levels; only women who used OC ⬎20 years had a 8.8 ⫾ 4.2 percentiles lower age-specific AMH compared to women who had used OC for a year or less. Being pregnant was associated with age-specific AMH values of almost 17 percentiles lower ( ⫽ 16.6; P ⬍ .0001) and having an irregular cycle with age-specific AMH values of 11 percentiles lower ( ⫽ 11, P ⬍ .0001). A significant trend was seen between parity and AMH. Lifestyle determinants There was no significant association between BMI ( ⫽ ⫺.2; P ⫽ .16), waist circumference ( ⫽ ⫺.09; P ⫽ .12), alcohol consumption ( ⫽ ⫺.4; P ⫽ .74), physical activity (p-ANOVA ⫽ 0.62), socioeconomic status (p-ANOVA ⫽ 0.62), and age-specific AMH. When determinants were modeled in clinically relevant categories instead of linear variables, there was still no significant association with age-specific AMH (Table 3). Smoking, however, was associated with lower AMH percentiles: Current smoking was associated with 3.6 percentiles lower age-specific AMH values (P ⫽ .02) in comparison to never smokers. Ex-smoking was not associated with lower AMH values ( ⫽ ⫺.6. P ⫽ .67). Daily smoking was associated with significant decreases in age-specific AMH. However, the number of cigarettes smoked daily and AMH does not seem to be related to AMH, as the number of percentiles difference of age-specific AMH with nonsmokers was similar for women who smoked 1–9 cigarettes per day ( ⫽ 2110 Dólleman et al Determinants of AMH J Clin Endocrinol Metab, May 2013, 98(5):2106 –2115 Table 3. Number of Percentiles that AMH Shifts in the Presence of a Specific Lifestyle Determinant Table 4. Multivariable Analysis of Determinants Linear Regression Linear Regression Determinants Anthropometrics BMI ⬍25 kg/m2 (normal) 25–30 kg/m2 (overweight) ⬎30 kg/m2 (obese) Waist circumference ⬍80 cm (normal) 80 – 88 cm (increased) ⬎88 cm (abdominal obesity) Smoking Never smoked Previous smoker Current smoker Number of cigarettes smoked per day in current smokers Smoking frequency in current smokers ⬍1 per month ⬍1 per day 1–9 per day 10 –19 per day ⱖ20 per day Number of pack-years in current/previous smokers Pack-years in categories 0 –5 5–10 10 –15 15–20 20 –25 ⱖ25 Alcohol Daily alcohol intake (yes/no) Number of alcoholic beverages daily Physical Exercise CPAI 1 (inactive) CPAI 2 (moderately inactive) CPAI 3 (moderately active) CPAI 4 (active) Social economic status SES 1 (lowest education level) SES 2 SES 3 SES 4 (highest education level) Percentiles of Change Standard Error P Value ⫺0.2 Reference ⫺2.5 0.2 .16 1.4 .08 2.4 0.06 .52 .12 1.49 1.5 .19 .12 Reference ⫺0.6 ⫺3.6 ⫺0.3 1.5 1.5 0.1 .67 .02 .06 Reference 1.3 ⫺12.8 ⫺12.3 ⫺11.8 ⫺0.3 7.2 6.5 6.2 6.3 0.09 .86 .05 .05 .06 .001 ⫺3.1 ⫺7.0 ⫺8.5 ⫺6.6 ⫺6.0 2.1 2.3 2.6 3.3 2.9 .15 .003 .001 .05 .04 ⫺0.4 1.3 .74 1.6 1.0 .12 ⫺5.1 4.2 .23 ⫺2.8 4.2 .50 ⫺4.4 Reference 4.1 .29 3.2 4.0 3.4 3.0 3.0 3.2 .28 .19 .29 ⫺1.6 ⫺0.09 Reference ⫺1.9 ⫺2.3 Reference Reference The association between lifestyle determinants and age-specific AMH is quantified as the number of percentiles that AMH shifts in the presence of a specific determinant. Corresponding standard error and P value are shown. Determinants Irregular cycle vs regular cycle Current OC-use vs regular cycle Current pregnancy vs regular cycle Current smoking vs nonsmoking Parity (per child) Percentiles of Change Standard Error P Value ⫺10.8 2.4 ⬍.0001 ⫺12.7 1.7 ⫺17.6 5.1 ⫺4.5 1.6 ⬍.001 1.4 0.9 .14 Multivariable analysis of the association between reproductive and lifestyle determinants and age-specific AMH. The association is quantified as the number of percentiles AMH shifts with the corresponding standard error and P value. ⫺12.8; P ⫽ .05) as for women who smoked 10 –19 cigarettes daily ( ⫽ ⫺12.3; P ⫽ .05) or more than 20 cigarettes daily ( ⫽ ⫺11.8; P ⫽ .06, respectively). Although the linear association between the number of packyears smoked and AMH was statistically significant ( ⫽ ⫺.3; P ⫽ .002), there was evidence for a threshold after which the number of pack-years becomes significant. Smoking 5–10 pack-years was not associated with significantly lower age-specific AMH values than smoking less than 5 pack-years ( ⫽ ⫺3.1, P ⫽ .15), but smoking more than 10 pack-years was associated with significantly lower age-specific AMH values. The magnitude of the association after 10 –15 pack-years ( ⫽ ⫺7.0, P ⫽ .003) was similar to 15–20 pack-years ( ⫽ ⫺8.5, P ⫽ .001) or 20 –25 pack-years (⫺6.6, P ⫽ .05). Results are displayed in Table 3. Multivariate analysis Table 4 shows that the variables that were significantly associated with age-specific AMH levels in the univariable analysis also remained significantly associated after multivariable adjustment. The magnitude of the effects of current smoking, current OC use, pregnancy, cycle irregularity, and parity remained largely the same in the multivariable models as in the univariable analysis. Only parity was no longer significant in the multivariate analysis after correcting for OC use, cycle irregularity, current pregnancy, and current smoking. Figure 2 shows the median AMH values according to the CG-LMS model in the 4 most clinically relevant subgroups: regularly cycling women and OC-taking women who did and did not smoke at the time of blood sampling for AMH measurement. In this figure, it is evident that the difference in AMH values between OC-taking women who did and did not smoke at the time of AMH measure- doi: 10.1210/jc.2012-3995 jcem.endojournals.org 2111 Figure 2. Bar graph showing mean (p50) AMH values with increasing age according to the CG-LMS model for women in 4 subgroups. ment was smaller than for regularly cycling women. A test for interaction between smoking and OC use was done to see if this would explain this discrepancy, but no significant interaction effect was found (P ⫽ .07). Discussion Main findings This large cohort study demonstrates that age-specific AMH levels are influenced by both reproductive factors and lifestyle determinants. More specifically, we found 2 distinct factors strongly associated with age-specific AMH levels: current use of oral contraceptives and current smoking. This knowledge will ameliorate our understanding of AMH dynamics and its usefulness as a screening or diagnosis tool in clinical practice. Findings in view of existing literature OC use at the time of blood sampling was associated with significantly lower age-specific AMH levels. AMH was 11 percentiles lower in current OC users compared to women with a regular cycle and 9 percentiles lower compared to women who had never taken OC. One would expect the effect of current OC use to be a weighted average between previous and current OC use (⫺0.3 and ⫺9.0 percentiles). However, due to the occurrence of current pregnancy in the group of women with previous OC use, the effect of current OC use is slightly lower than expected. This effect of OC use was seen across all ages and for all percentiles of AMH. The finding is not entirely consistent with literature. Several studies have suggested AMH to remain constant under the influence of exogenous sex steroids used for contraception (15, 21–24). However, these studies consisted of small numbers, and none assessed age-specific AMH levels. Other studies have revealed a significant decrease in AMH during exposure to OC (13, 14, 16, 35). Last, one prospective longitudinal study observed an increase in AMH values of approximately 23% after discontinuation of OC, which supports our notion of the reversibility of the effect of OC (17). The observed reduction in AMH among OC users is unlikely to be due to depletion of the primordial follicle pool as OC users do not experience natural menopause at an earlier age (36, 37). Furthermore, in women who were previous OC users, AMH levels were similar to nonusers, suggesting that the effect is reversible. The decrease in AMH among current OC users is therefore more likely to be due to down-regulation of the hypothalamic-pituitaryovarian axis by OC resulting in diminished FSH and LH production and consequent altered development of the antral follicle cohort (14, 38). It has also been argued that AMH must be partially gonadotropin responsive as FSH can directly stimulate AMH production from granulosa cells in vitro (39, 40). However, direct stimulation by endogenous or exogenous FSH rises has not elicited any response in serum AMH levels (41). Therefore, most likely, 2112 Dólleman et al Determinants of AMH we may theorize that OC-induced arrest of follicular growth and decreased support of growing follicles by FSH causes AMH levels to be diminished. This notion is supported by several studies that observe a decrease in follicle size and ovarian volume (14, 22, 23, 42) and other studies that observe a decrease in antral follicle numbers (16, 23). Furthermore, FSH is an important survival factor for the AMH-producing preantral and early antral follicles (43). As these are the stages of follicle development during which most follicles undergo atresia (44), OC-induced suppression of FSH may also result in either increased apoptosis or decreased follicle functionality. This combined effect of smaller numbers of follicles and diminished follicle functionality from decreased FSH support is a very plausible explanation for the lower AMH values observed in this study. All the above arguments may also apply to the association between pregnancy and reduced AMH observed in this study and a previous longitudinal study as pregnancy is a transient condition with severely suppressed endogenous FSH (45). However, during pregnancy the GnRH suppression is induced by endogenously increased levels of estrogens instead of by exogenously administered drugs (46). Further research is needed to assess whether AMH levels measured under OC use are correlated with natural cycle AMH measures. By doing so it can be determined whether AMH under OC use is an adequate reflection of individual ovarian reserve and not just the individual degree of suppression by OC. Interestingly, van den Berg et al showed AMH levels on day 7 of the pill-free interval to be highly correlated with AMH levels after discontinuation of the pill (17). Similarly, Nelson et al showed pregnant AMH measures to be highly correlated with nonpregnant measures (45), indicating a proportional relationship. This study showed that cycle irregularity was associated with significantly lower age-specific AMH levels than AMH levels in women with a regular cycle. This finding is difficult to interpret, as this group encompasses women with an oligomenorrhea associated with polycystic ovary syndrome (PCOS; high age-specific AMH levels), women with irregular menstrual cycles associated with the menopausal transition (low or undetectable AMH levels), women with postpartum cycle arrest, or unexplained cycle irregularity. In our study the mean age of women with an irregular cycle was 44.6 years (⫾9 years), arguing that in a proportion of these women cycle irregularity will be explained by the occurrence of the menopausal transition. This also explains the discrepancy with a recent article that showed women with cycle irregularity to have higher AMH values: in this population the mean age was 26.6 years and therefore high AMH values and cycle irregularity will more likely pertain to the occurrence of PCOS (47). J Clin Endocrinol Metab, May 2013, 98(5):2106 –2115 Our results also showed that women who have given birth to more children are likely to have significantly higher AMH levels. Recent prospective studies have shown that having a high AMH is associated with a higher age at menopause (4, 48, 49). As a timed interval of approximately 10 years is suggested to be present between the final menstrual period and the end of natural fertility, it is conceivable that the time window to conceive is longer in women with high age-specific AMH levels, thus potentially resulting in more childbirths (50). One small study of 294 women aged 21 to 22 years paradoxically showed that a lower AMH was associated with a higher parity and a higher age at menarche. However, in this study contraceptive use was not taken into account, hindering direct comparison to our study. It is conceivable that women with a higher parity may be more likely to take contraceptive measures, which may explain lower AMH values. Furthermore, the sample of women who conceived 2 or more children was very small (only 9 women had 3 or more children), which may not be a representative sample from which to draw such conclusions. With regard to age at menarche, their finding is paradoxical with most literature, as one would expect women with a high AMH to experience menarche later due to the occurrence of PCOS. Without correcting for contraceptive use, however, inferences based on these results may be risky (51). Of the lifestyle factors investigated, current smoking was most strongly inversely associated with AMH concentration. This is in line with existing research (13, 18, 19). Although the effect of smoking was dose-dependent in the sense that one had to smoke at least daily, the effect was similar in women who smoked 1–10 cigarettes daily as women who smoked more than 20 cigarettes daily. There was a similar association with the number of packyears smoked, where a significant association was seen after 10 –15 years, but after 15 pack-years the magnitude of the effect did not change very much for women who smoked more than 20 pack-years. Previous smoking was not significantly associated with decreased AMH in both our study and a previous article (18). Translated to a clinical setting, our results thus suggest that if a low age-specific AMH level is measured in a woman of reproductive age, advising her to stop smoking may be beneficial for her AMH levels. Our results suggest that the association between AMH and smoking is similar to the association between age at natural menopause and smoking as both are dose responsive and both effects diminish after quitting smoking (26, 52, 53). The reversibility of the effect of smoking on AMH and age at natural menopause is contradictory to the theory that the toxic effect of smoking on ovarian follicles results in earlier depletion of the primordial follicle pool, as such an effect would be irreversible doi: 10.1210/jc.2012-3995 (26). Several other explanations could exist. First, although toxicity to human follicles has been confirmed (54), current smoking may only influence preantral and antral follicles but not primordial follicles (18). The alternation of the functionality of the antral follicle pool would explain lower AMH levels and, if the primordial pool remained unaltered by smoking, quitting smoking would allow both restoration of the growing follicle pool and normalization of AMH (18). Alternatively, smoking may alter steroidogenesis or the hypothalamic-pituitary-ovarian axis, as suggested by studies that indicate altered levels of sex hormones among smokers (19). This could also lead to lower antral follicle counts and decreased AMH values. The lower age at menopause in smokers could then be explained, not by earlier depletion of the primordial follicle pool, but by the number of antral follicles becoming too small to sustain monthly menstrual cycles. More research is needed to elucidate the exact mechanisms between smoking and measures of ovarian reserve. There was no association between BMI and AMH. This is in line with some (55–57) but not all previous studies (9, 15, 58). It is important to note that the BMI in our study sample was very homogenous with few obese women (mean BMI ⫽ 24.3 ⫾ 3.9 SD). Strengths and weaknesses The most important strengths of the present cohort are the large size of the cohort, the fact that it is populationbased, and the extensive measurements and inventories on lifestyle factors and menstrual cycle characteristics that were collected starting at a relatively young age of 20 years. Also, the statistical analysis, using the CG-LMS model, provides advantages over classical approaches. Usually, linear regression is used with AMH on a log-scale to model the age related decline of AMH. The effect of determinants can then be tested with multivariate regression analysis while correcting for age. The LMS model has an advantage over this linear regression model as it does not assume that the skewness, the median, and the coefficient of variation are the same at different ages but models them as a function of age. In this way age is more appropriately corrected for when assessing the influence of possible determinants on AMH concentrations. Last, the AMH Gen II assay (Beckman Coulter Ltd) was used, which is believed to be the newest most generalizable measure of AMH. The samples were determined in a single laboratory, by the same experienced laboratory technician, and the precision of assay results was validated with linearity-of-dilution assessment. Samples were frozen within 12 hours and cryo-preserved within 6 weeks. Efficiency reasons required all samples to go through one temperature-controlled freeze-thaw cycle before the jcem.endojournals.org 2113 AMH assay was performed. These are all factors that argue for the presence of homogeneous specimen processing and supports that we have provided reliable, reproducible AMH measures (59). However, the Gentech II assay remains a manual ELISA. Future automated ELISAs may provide even more stable measures of AMH. We did not time the collection of our blood samples on the same menstrual cycle day for all participants. However, it has been shown that intracycle fluctuation in AMH does not follow classical endocrine patterns, but that it occurs randomly throughout the menstrual cycle, thus supporting our choice of protocol (60). One weakness of the current study might be that there is just one measure of AMH per woman; furthermore, the cross-sectional approach used in this study did not allow us to assess all aspects of AMH suppression by certain determinants. However we sought to make the situation in our study most comparable to clinical practice in which a physician is usually confronted with just one AMH measure. In such a situation it is important that the physician is aware of which factors may have had an influence on the AMH level that he is confronted with. Clinical implications The impact of the studied determinants for clinical interpretation depends on whether a woman has a high or a low AMH for her age to start with. If a woman is above the 75th percentile of AMH for her age, a considerable drop to a lower percentile may not be problematic, but for a woman in the 30th percentile, it is conceivable that the effect may be worrisome. Current smoking was associated with a decrease of AMH of 4 percentiles. For a 26-year-old woman this means that if she were in the 50th percentile of AMH without smoking she would be in the 46th percentile if she did smoke. This is comparable to a woman of 28 years in the 50th percentile. Current smoking thus adds 2 years to her reproductive age in this example. The same calculation can be done for a 36-year-old woman in the 50th percentile in which case her AMH would be comparable to a 37- to 38-year-old woman if she were to smoke. For a 40-year-old woman it would thus add 1.5 years to her reproductive age. AMH is increasingly applied in clinical practice. Several studies have presented nomograms for age-specific AMH values in a variety of populations with AMH measured with a variety of assays (7–12). This study shows that AMH concentrations are influenced by several determinants and may thus aid in the interpretation of AMH results. Future studies on the effects of determinants on AMH would benefit from a prospective longitudinal design to help elucidate the precise mechanisms behind AMH suppression. The future clinical implications of hav- 2114 Dólleman et al Determinants of AMH ing a high or low AMH for one’s age are largely unknown. More large-scale, long-term prospective studies are needed to assess the impact of having a low or high agespecific AMH. Until this has been done, there is no concrete place for AMH nomograms in a clinical setting. Conclusion In conclusion, our study adds valuable information to the body of knowledge currently available on AMH in the general population. The lower AMH levels associated with OC use and smoking seem reversible, as effects were confined to current use. It is important to give careful consideration to the effect of such determinants when interpreting AMH in a clinical setting. Acknowledgments We thank J.W.J.M. Cremers for technical assistance with AMH determinations. Address all correspondence and requests for reprints to: M. Dólleman, University Medical Center Utrecht, Room 05.126, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands. E-mail: [email protected]. No funding was received for the writing of this manuscript. Disclosure Summary: M.D., W.M.M.V., M.J.C.E., M.E.T.D., E.H.J.M., and Y.T.S. have nothing to disclose. F.J.B. has received fees and grant support from the following companies: Ferring, Gedeon Richter, Merck Serono, Medical Specialties Distributors, and Roche. J Clin Endocrinol Metab, May 2013, 98(5):2106 –2115 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. References 1. 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