How to Read Penis Size Percentile Charts
Asian J Androl. 2018 Nov-December; 20(6): 567–571.
Male person external genitalia growth curves and charts for children and adolescents anile 0 to 17 years in Chongqing, China
Yi-Nan Wang
1Department of Medical Statistics and Information Direction, School of Public Wellness and Management, Chongqing Medical Academy, Chongqing 400016, China
Qing Zeng
oneSection of Medical Statistics and Data Direction, School of Public Wellness and Management, Chongqing Medical University, Chongqing 400016, Cathay
Feng Xiong
2Department of Endocrinology, the Children's Hospital of Chongqing Medical Academy, Chongqing 400014, China
Yan Zeng
iiDepartment of Endocrinology, the Children'south Hospital of Chongqing Medical University, Chongqing 400014, Communist china
Received 2017 Dec 15; Accepted 2018 May 17.
Abstruse
Genital size is a crucial index for the cess of male sexual development, equally abnormal penile or testicular size may be the earliest visible clinical manifestation of some diseases. Notwithstanding, there is a lack of data regarding penile and testicular size measurements for Chinese boys at all stages of childhood and puberty. This cantankerous-sectional written report aimed to develop advisable growth curves and charts for male external genitalia among children and adolescents aged 0–17 years in Chongqing, China. A total of 2974 boys were enrolled in the present written report. Penile length was measured using a rigid ruler, penile diameter was measured using a pachymeter, and testicular volume was determined using a Prader orchidometer. Historic period-specific percentile curves for penile length, penile diameter, and testicular volume were drawn using the generalized additive models for location, scale, and shape. Very similar growth curves were found for both penile length and penile diameter. Both of them gradually rose to 10 years of age so sharply increased from 11 to 15 years of age. Nonetheless, testicular book changed trivial before the historic period of 10 years. This study contributes to the literature covering age-specific growth curve and charts about male external genitalia in Chinese children and adolescents. These age-related values are valuable in evaluating the growth and development status of male external genitalia and could exist helpful in diagnosing genital disorders.
Keywords: adolescents, children, generalized additive model for location, scale, and shape, growth curves, penile size, testicular volume
INTRODUCTION
In males, external genitalia serve important physiologic functions, especially for fertility. Consultations with patients and their parents regarding the size of the penis and testes are very mutual in pediatric, urologic, endocrinologic, and surgical clinics.1 Genital size is a crucial index for the assessment of male sexual evolution: abnormal penile or testicular size may exist the earliest visible clinical manifestation of hypogonadotropic hypogonadism, main hypogonadism, androgen insensitivity, and genetic syndromes, including Klinefelter, Kallmann, Prader–Willi, and Laurence–Moon–Biedl syndromes. For this reason, an early diagnosis of abnormal size in penile or testicular is important for both medical and psychological therapy. Historic period-specific curves and charts are a uncomplicated and rapid approach for early evaluation and diagnosis for abnormal genital size.
The generalized additive model for location, scale, and shape (GAMLSS) provides a growth curve that allows the user to blueprint distribution parameters as a function of an explanatory variable (e.grand., historic period). It has been used by the Multicentre Growth Reference Study (MGRS) of World Health Organization (WHO) group in constructing growth reference curves for school-age children and adolescents.ii GAMLSS is also widely used to develop various growth references for such characteristics equally lung function,three birth weight,4 grip forcefulness,five and blood pressure.6 However, information technology has not been used to develop growth curves for assessing male person external genitalia. GAMLSS-based growth curves could provide an advisable assessment tool for smaller penises and testes and allow for the appropriate comparisons among different groups of children or adolescents.
Previous studies have confirmed the existence of ethnic differences regarding the size of the penis and testes.seven,8,9 Normal growth curves and tables for the male person penis take been reported for several different countries.10,11,12,13,xiv,15,sixteen,17,18 Withal, most of the previous studies have applied only penile length measurements in newborns or prepubertal boys;10,xi,12,13,14 at that place is no report evaluating both penile and testicular size measurements in Chinese boys roofing all stages of babyhood and puberty.
The purpose of the present written report was to develop age-specific percentile growth curves for assessing penile length, penile diameter, and testicular volume in Chinese male person children and adolescents aged 0–17 years.
PARTICIPANTS AND METHODS
Subjects
A cross-sectional written report was performed between December 2014 and December 2015 at the concrete test center of the Children'southward Hospital of Chongqing Medical Academy (Chongqing, Communist china). The study subjects were infants and preschool children from outpatient clinics who did not nowadays a illness involving to their genitals. Parental consent was obtained at the time of enrollment in the study. Subjects younger than vii years former were defined as preschool children; subjects aged 7 years–17 years, eleven months were divers every bit school-age children and adolescents. Random cluster sampling was used to recruit school-age children and adolescents from the Chongqing expanse. Iii primary schools, iii secondary schools, and ane high school were selected every bit the sampling sites. The subjects were stratified past grade, with classes serving as units. All boys belonging to the sample grouping were initially included, and those who did not wish to participate were excluded. Researchers collected informed consent from all participants or their parents. This study was approved by the Research Ethics Committee of Chongqing Medical University.
Measurements
All measurements were performed in a room at a warm and comfortable temperature. The superlative was measured without shoes using a digital calibration, and their weight was recorded while they were wearing only a T-shirt and underpants. Body mass alphabetize (BMI) was calculated from the aforementioned measured weight and acme data through the formula weight/height2 (kg m−2). Genital assessment was conducted by two trained investigators using the same measurement technique, with the subjects in the supine position. The stretched penile length (SPL) during the flaccid state was measured with a rigid centimeter ruler from the pubic ramus to the tip of glans under gentle painless extension of penis using Schonfeld's method.17 The fatty tissue in the prepubic area was mildly compressed with one end of the ruler down to the pubic ramus. Penile diameter was measured using a pachymeter at the mid-point of the penile shaft. Testicular volume was evaluated with a Prader orchidometer, and the values of the left and right testes were given separately. The mean value was recorded if the interobserver variation was <0.5 cm (for penile length and penile diameter) or 0.five ml (for testicular book). Repeated measurements were adopted when variation was greater than or equal to these values.
Statistical analyses
The data were double-entered into a database (EpiData version 3.one http://www.epidata.dk/). Boys aged <1 year were assigned to the 0-year group; boys aged 1 yr, 0 mean solar day to 2 years were assigned to the 1-year grouping; boys aged two years, 0 day to 3 years were assigned to the 2-year grouping, then on. To precisely represent the population of all children and adolescents, the obvious outliers were excluded. Outliers were identified using Tukey'due south methodology.19 The interquartile range (IQR) was calculated and outliers were identified as whatsoever value greater than 1.5 times IQR beneath the first quartile or to a higher place the third quartile. The Shapiro–Wilk examination was used to examine the normality of the data distribution for penile length, penile diameter, and testicular book. A t-exam was used to compare the differences between 2 groups, and P < 0.05 was considered statistically significant.
We estimated penile length, penile bore, and testicular volume percentile curves for children and adolescents by age using the GAMLSS model for the Box-Cox Power Exponential (BCPE) or the Box-Cox Cole Green (BCCG) distribution with cubic-spline smoothing.20 The BCPE distribution can exist described using four parameters: Grand for median, S for coefficient of variation, L for Box-Cox transformation power, and T every bit a parameter related to kurtosis. The Bayesian Information Benchmark (BIC) was used to identify the best model, here found to be that with the smallest BIC value. The final all-time models were based on the BCPE distribution for penile length, penile bore, and mean testicular volume. The 3rd, xth, 25th, 50th, 75thursday, 90th, and 97thursday percentile values were calculated by historic period for penile length, penile diameter, and hateful testicular volume separately. All statistical analyses were performed using the GAMLSS (5.0–one) library21 running R (version 3.three.3 world wide web.r-project.org) for Windows.
RESULTS
A total of 3033 boys underwent genital size measurement during the written report period. An application of Tukey'southward method resulted in 59 records (1.9% of the observations) beingness outliers. Thus, a total of 2974 children and adolescents for further analysis were included in the terminal database.
The Shapiro–Wilk exam results showed that SPL followed a normal distribution for the 15-year (P = 0.1578) and 17-year historic period groups (P = 0.3549), but not for other historic period groups (P < 0.01). In addition, neither penile diameter nor the book of the left or right testes followed a normal distribution in any age grouping (all P < 0.01). At that place was no pregnant difference in testicular volume between the left and right testes in any age grouping (all P > 0.05).
The mean values and standard deviations (due south.d.) for height, weight, BMI, penile length, penile bore, and left and right testicular volumes for children and adolescents in each age grouping are shown in Table 1 . The age-specific smoothed percentile values (due east.g. 3rd, xth, 25th, fiftyth, 75th, 90th, and 97th) for penile length, penile diameter, and mean testicular volume by age are shown in Table ii . The age-specific smoothed percentile curves for male external genitalia by age are shown in Figure 1 and two .
Table 1
Height, weight, trunk mass alphabetize, penile length, penile diameter, and testicular volume for Chinese children and adolescents by each age group (mean±due south.d.)
Table two
Smoothed percentiles for penile length, penile diameter and testicular volume in males aged 0–17 years of China
Smoothed percentile curves for (a) penile length and (b) penile diameter past age, P3, P10, P25, P50, P75, P90, and P97 indicate iiird, 10th, 25thursday, lth, 75th, ninetythursday, and 97thursday percentiles, respectively.
Smoothed percentile curves for mean testicular volume by historic period, P3, P10, P25, P50, P75, P90, and P97 indicate 3rd, xth, 25th, lthursday, 75thursday, 90th, and 97th percentiles, respectively.
The growth of penile length increased rapidly in the anest twelvemonth of life, then gradually began to increase until x years of historic period. A marked increase was observed betwixt 11 and 15 years of historic period. After this, penile growth was relatively deadening and changed little ( Effigy 1a ). The growth of penile bore was similar to that of penile length, showing pronounced growth betwixt 0 and 3 years of age, and again after age eleven ( Figure 1b ). Testicular volume showed almost no change before the age of ten years; there was just a 1–ii ml increase during the commencement x years of life. However, testicular size increased sharply from 11 to xvi years of age, after which, the slope of the curve progressively declined, indicating a much slower increment in testicular volume ( Figure ii ).
Give-and-take
Studies that listing the growth curves of penile size are non uncommon; nonetheless, the normal range for these studies has been described in terms of hateful ± s.d.11,thirteen,16 Those studies exercise not usually shine the standard curves using appropriate distribution, such every bit a log normal or Box-Cox Ability Exponential distribution with a cubic-smoothing spline function. The lack of smoothing may lead to very irregular growth curves, fifty-fifty with large sample sizes. In addition, diverse investigators have reported indigenous differences for penile size and testicular volume.7,8,22 According to Fok et al.,8 total-term Chinese infants accept shorter penises than other Asian counterparts and Caucasians, which ways that Chinese children may be diagnosed with micropenis if no appropriate local reference values are available. Using the GAMLSS method, our study provided an age-specific growth curve and chart for penile length, penile diameter, and testicular volume for Chinese boys between the ages of 0 and 17 years, which has not been previously used to evaluate the development of male external genitalia.
Abnormal size of the penis and testes could exist the earliest visible clinical manifestation of deficiencies in the function of hypothalamic-pituitary-gonadal (HPG) centrality and the secretion of related hormones, so precise measurement of penis and testes is a precondition of assessment. Since its initial employ by Schonfeld and Beebe,17 SPL has been considered the gilt standard for measurement of penile length, and it has been utilized in various studies.viii,nine,10,11,12,13,14,15,xvi Smith et al.23 successfully used ultrasonography for penile measurement and establish at that place to exist a significant difference between ultrasonography and conventional methods of penile measurement. Nonetheless, further studies are all the same needed to appraise the limitation of the ultrasonography in the measurement of larger penises. Ultrasonography is also used for measurement of testicular volume. Goede et al.24 assessed the validity of the Prader orchidometer per age group by comparison its founding to volume measurements made by ultrasonography, and a shut correlation was found betwixt these ii modalities (R 2 = 0.956). These results revealed that volume equally measured using the Prader orchidometer tin serve as a valid method for monitoring testicular growth. Given the inconvenience and high cost of ultrasonography for large groups of subjects, classical measurements for testicular size such equally those involving the orchidometer are a practical option. Furthermore, a strict quality control by the experienced doctors provided a guarantee in the accuracy of the measurements.
In that location is no full general understanding as to the blueprint of penile growth. A previous study by Schonfeld and Beebe17 reported that the penis grows slowly to the age of 5 years, followed by a relatively steady phase. Growth and so increases rapidly during puberty. This blueprint of penile growth was also demonstrated in a study of penile size performed in Brazil.15 Nevertheless, in our study, we found that penile length increased continuously afterwards birth, showing tiptop growth from 11 to 15 years of historic period. This is similar to findings reported in other studies in Korea16 and Bulgaria.18
In the present written report, we also constitute a greater growth rate for penile length in the first year after nascency. Similarly, Boas et al.25 reported that a rapid increase in penile growth took place during the outset 3 months after nativity, coinciding with an babe's high concentrations of testosterone. The report made by Camurdan et al.11 indicated that the quickest increase in penile length took place during in the first six months after birth. In a Japanese study, penile size increased continuously throughout the pre-pubertal period, and about rapidly during the first four months of life.14 Information technology is known that the development of the penis depends on the levels of testosterone in the trunk, and in healthy males, the HPG axis is transiently activated during the kickoff month of postnatal life. The gonadal hormones and gonadotropins increase to a pubertal or even adult levels (then-called "mini-puberty"), followed by a relatively quiescent period until reactivation of the HPG in puberty.26,27
When comparing the growth curves for the penis and testes, we can readily observe that testicular enlargement precedes rapid lengthening of the penis. The increase in the testes in our study took identify up to one year before than the increase in penile size. This developmental pattern for male external genitalia is consequent with developmental sequences.xviii According to Tanner et al.,28 the benchmark for the onset of puberty is testicular volume, non penile length. Testicular volumes of 4 and 12 ml represent the first clear sign of the pubertal increase, and the attainment of mid- or belatedly puberty, respectively. The boys whose testicular volume reached an average of 4 ml in our written report were virtually 10 to 11 years of age, and the testes reached an average of 12 ml at an historic period of xiii–xiv years. This finding was similar to a survey from the Chinese Medical Association, which constitute that the median age at onset of puberty for urban Chinese boys as indicated by a testicular volume of four ml or more was 10.55 (95% CI 10.27–x.79) years, and for 12 ml or more than was 13.42 (95% CI 13.04–13.79) years.29
From our results, we were able to demonstrate the wide differences between the 3rd and 97thursday percentiles. For instance, the penis of 14-year-old boy had a hateful (s.d.) length of 8.20 (0.72) cm (iiird–97thursday percentile: half-dozen.76–9.06 cm); the testes had a mean (southward.d.) volume of xiii.14 (4.58) ml (3rd–97thursday percentile: 6.27–23.38 ml). These findings are near likely due to the fact that, during adolescence, people of the same historic period can be at unlike stages of sexual development. In a contempo article by Soydan et al.,30 males aged 13–xv years were evaluated, and profound variability in penile length was detected within the same age grouping. These authors stated that penile length during puberty should be evaluated individually co-ordinate to the child's current pubertal stage. For this reason, we suggest that the large variations exist taken into consideration when evaluating growth and development in normal boys of the same historic period, especially during puberty.
Our study has several strengths. First, this was a large cantankerous-sectional population-based study of the growth of male external genitalia in China and it covered all stages of childhood and puberty. 2d, we used an avant-garde statistical method to plant predictive percentiles for penile length, penile bore, and testicular book. Third, the age-specific percentile values provided by this study were highly suitable for use in clinical practice. Withal, several limitations should be noted. First, only urban boys were included in our study, which may non adequately represent the population of other areas in China. Second, the study was cantankerous-sectional blueprint. Conspicuously, there is a need to substantiate these findings in a longitudinal written report. Tertiary, testicular volume was measured using conventional Prader ochidometer. However, the Prader ochidometer might overestimate the testicular volume in small testes.31 Quaternary, we did not here take into account the potential affect of recognized determinants of male external genitalia, such as height, weight, or BMI, on the percentile values presented. The paucity of information in this area requires further enquiry.
CONCLUSIONS
To the all-time of our cognition, nosotros have developed the get-go age-specific smoothed percentile curves for penile length, penile diameter, and testicular volume for Chinese boys aged 0 to 17 years using the pop GAMLSS method. These historic period-specific percentile values may be helpful in informing the clinical assessments of penile size and testicular size to assist with the prompt diagnosis of genital abnormalities.
AUTHOR CONTRIBUTIONS
YNW was responsible for literature consulting, information analysis, and manuscript writing. YZ conceived and designed this study and engaged in data collection and entry. QZ contributed to statistical analysis and completion of final manuscript. FX participated in the study design and supervision. All authors read and canonical the final manuscript.
COMPETING INTERESTS
All authors declared no competing interests.
ACKNOWLEDGMENTS
We appreciate the generous contribution of boys and their parents who participated in this study. We also thank the support in measuring engineering of the Department of Endocrinology, the Children's Hospital of Chongqing Medical Academy.
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219296/
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