the study protocol was approved by the ethics committee of the ministry of health and the school boards .
a total number of 30 clusters including 7,493 girls ( aged 620 years ) were selected .
students with a history of acute or chronic diseases or any chronic medication use were excluded . in all subjects , height , weight , and pubertal stages
general physicians determined pubertal stages under the supervision of specialists by visual inspection and palpation , using the criteria and definitions described by marshall and tanner.10 accordingly , breast stages 15 were determined by both inspection and palpation .
breast stage b2 corresponded to the breast bud stage with palpable glandular breast tissue and elevation of the papilla , stage b3 with further enlargement of the breast and areola with no separation of the contours , stage b4 where the areola and papilla form a secondary mound above the level of the breast , and stage b5 was assigned in case of the mature breast with projection of the papilla only .
the onset of puberty was measured as the age at breast development at tanner stage 2 ( b2 ) .
stage ph2 was assigned with the presence of long , slightly pigmented hair ( straight or curled ) .
participants were grouped by 1-year age intervals , which extended from the day of their birthday to the day before the next birthday . for comparison of different areas
, we used the national classification of the provinces according to their climate , ethnicity of the population , geographic locations , and socioeconomic variables .
classification of iranian provinces to regions according to climate , geographic location , ethnicity and socioeconomic status we estimated the mean of the time of men - arche , b2-b5 and ph2-ph5 stages .
statistical analysis was done using spss version 15 ( spss , chicago , il ) .
analysis of variance ( anova ) and post - hoc tests were used to compare the mean ages of menarche , pubarche , and telarche in different regions .
we estimated the mean of the time of men - arche , b2-b5 and ph2-ph5 stages .
statistical analysis was done using spss version 15 ( spss , chicago , il ) .
analysis of variance ( anova ) and post - hoc tests were used to compare the mean ages of menarche , pubarche , and telarche in different regions .
we estimated the mean of the time of men - arche , b2-b5 and ph2-ph5 stages .
statistical analysis was done using spss version 15 ( spss , chicago , il ) .
analysis of variance ( anova ) and post - hoc tests were used to compare the mean ages of menarche , pubarche , and telarche in different regions .
tehran had the lowest mean age of menarche , being 11.99  1.35 years , which was significantly lower than other 10 regions .
the second region with lowest age at menarche was fars ( 12.40  1.27 years ) .
the mean age at b2 stage of breast development was significantly lower in ghazvin - zanjan region ( 8.97  1.45 years ) followed by the region consisting of khorasan jonobi and sistan balochestan ( 10.11  1.61 years ; p = 0.003 ) , boshehr - khouzestan region ( 10.05  1.21 years ; p = 0.01 ) , tehran - relatd cities ( 10.46  1.67 years ; p < 0.0001 ) , fars ( 11.01  1.88 years ; p < 0.0001 ) and kordestan - lorestan - ilam region ( 9.94  1.25 years ; p = 0.02 ) . in fars region , the mean age at b2 stage of breast development ( 11.01  1.88 years ) was higher than other regions except for mazendran - guilan and tehran - related cities regions .
figure 2 shows the mean age at b1-b5 of breast development in different regions in iran .
mean age ( years ) at menarche in different regions mean age ( years ) at various stages of telarche in different regions in iran the mean age at ph2 stage of pubarche in kordestan - lorestan - ilam region ( 10.70  1.23 years ) was significantly higher than khorasan jonobi - sistan balochestan region ( p < 0.0001 ) , boshehr - khozestan region ( p < 0.0001 ) , tehran - relatd cities ( p < 0.0001 ) , chaharmahal - kerman - isfahan region ( p < 0.0001 ) , ghazvin - zanjan region ( p < 0.0001 ) , and boshehr - khozestan region ( p < 0.0001 ) .
the mean age at ph2-ph5 of pubic hair development in different geographic locations of iran is presented in figure 3 .
to the best of our knowledge , this is the first study of its kind to compare the pubertal stages in different geographic locations in a country .
it should be acknowledged that such comparison is not feasible in many countries with small population and no significant diversity in climate and other geographic characteristics .
we found that the mean age of menarche was significantly lower in tehran than all other regions .
tehran province , including the metropolitan city of tehran , is located in central part of the country with multiethnic population .
not only multi - ethnicity but also higher socioeconomic status and more industrialized lifestyle habits in tehran might be associated with earlier menarche age . in another study
the mean age of menarche was 12.68 years in tehran in 2004.11 in our study conducted 2 years later , this age decreased to 11.99  1.35 years . decreasing trend of menarche age
is observed in many developed and developing countries.1213 it might be attributed to changes in socioeconomic status of people14 and increasing rate of obesity.12 ethnicity is documented as a factor that describes some international varieties of puberty age.1516 in the current study , the mean age at menarche and ph2 was higher in girls with kurd ethnicity than in other ethnicities .
kurd ethnicity is the third most prevalent ethnicity in iran after persian and azeri ethnicities .
it can be suggested that the higher age of puberty in girls of this region might be attributed to their ethnicity as well as the cold climate and their high altitude mountainous region of living .
in addition to ethnicity , the geographic characteristics may influence the age of puberty . in our study , the lowest mean age at b2
was documented in zanjan - ghazvin region , with mediterranean weather and spring rains , and population of azeri ethnicity .
the earlier telarche in this region in comparison to other regions with azeri population might be attributed to environmental factors .
premature telarche is suggested to be associated with endocrine disrupting chemicals found in pesticides and plastics , with possible estrogenic and androgenic activities.1718 further investigations on environmental pollution might be necessary in this regard .
the considerably high prevalence of overweight among young iranian children19 might decrease the age of puberty in the near future .
the main limitation of this study was its cross sectional nature , and as a result , casualty can not be ascertained .
in addition , we considered the prominent ethnicity in each region ; but some participants might have other ethnicities .
we found significant differences in the age of pubertal stages of girls living in various regions with different ethnicity and geographic characteristics .
considering the impact of pubertal age on general health , more studies should be done about the lifestyle and environmental factors affecting the onset of puberty .
mem participated in the design and conducting the study ; ar participated in the design and conducting the study and helped to draft the manuscript ; rk drafted and edited the manuscript ; pm conducted the statistical analyses and helped to draft the manuscript ; ss participated in conducting the study ; ga participated in the design and conducting the study ; ha participated in conducting the study ; np participated in conducting the study ; sk in conducting the study ; pp helped to draft and edit the manuscript ; as participated in conducting the study .
 background : this study aimed to compare the timing of puberty between various geographic locations and different ethnicities.methods:this national survey was conducted in 20 provinces in iran . 
 healthy iranian girls were selected from public schools using cluster random sampling . 
 a total number of 30 clusters including 7493 girls , aged 6.020 years , were selected . in order to compare different areas , the national classification of the provinces based on climate , ethnicity , geographic locations , and socioeconomic variables were used . 
 accordingly , there are 11 regions in iran . 
 analysis of variance was used to compare the mean ages of menarche , pubarche , and thelarche in different regions.results:tehranian girls , with 11.99  1.35 years ( mean  sd ) , had the lowest age of menarche which was statistically significantly . 
 the second region with lowest age at menarche was fars ( 12.40  1.27 years ) . 
 the mean age at breast bud stage ( b2 ) was significantly lower in ghazvin - zanjan region ( 8.97  1.45 years ) . in fars region , 
 the mean age at b2 stage of breast development ( 11.01  1.88 years ) was higher than other regions except for mazendran - guilan and tehran - related cities . 
 the mean age at public hair development at tanner stage 2 ( ph2 ) in kordestan - lorestan - ilam region ( 10.70  1.23 years ) was significantly higher than other regions.conclusions:we found significant differences in the age of pubertal stages of girls living in various regions with different ethnicity and geographic characteristics . 
 considering the impact of pubertal age on general health , more studies should be done about the lifestyle and environmental factors affecting the onset of puberty . 