Assessment of the stretched penile length in Sri Lankan newborns

Method This was a cross sectional observational study, carried out at post natal wards of the Castle Street Hospital for Women, Sri Lanka. The study was done on 369 stable newborns delivered at the gestational age of 37 to 42 weeks. A complete neonatal examination was performed by the principal investigator and the measurements of the weight, length, head circumference and stretched penile length were obtained. Mean penile length and statistically significant difference of penile length (SD) values were calculated. The correlation of mean penile length, period of gestation, birth weight and length were analysed.

Development of testes in a male embryo begins around 6-7 weeks of gestation, from the genital tubercle. Differentiation of sertoli cells in an embryo commences around 6-7 weeks of gestation and Leydig cells are visualized by 11 weeks of gestation [1]. Sertoli cells begin to secrete Anti Mullerian Hormone around the 7 th week of gestation and Leydig cells start secreting Testosterone around 11th to 12 th weeks of gestation [1]. Placental Human Chorionic Gonadotrophin-testes axis stimulates Leydig cells from 8 th to 14 th weeks, while foetal Hypothalamic-Pituitary-Gonadal axis activation occurs around 15th week of gestation [1,2]. The onset of foetal penile growth which is dependent on the foetal androgen exposure, occurs at 8 th to 14 th weeks of gestation and a rapid growth is observed at 7mm/week from 14 weeks to term [1,2]. Following this growth period, another period of rapid growth occurs at mini-puberty, during the first 3 months of life [2,3]. In the foetus, growth of the penis is due to the action of testosterone and dihydrotestosterone during the second and third trimester, which is regulated by Luteinizing hormone [4].
Micropenis with undescended testes is a feature of underlying congenital hypopituitarism, which is associated with hypogonadotropic hypogonadism [2,5]. It is also seen in syndromes such as Klinefelter, Prader Willi, Noonan [2,5]. Ambiguous genitalia in an under virialized male with hypospadias and undescended testes may be the initial presentation of a rare form of congenital adrenal hyperplasia [5]. Micropenis or small phallus with varying degrees of hypospadias may be the only identifiable feature of a Disorder of Sex Development (DSD) in the neonate [5]. Therefore, it is very important to identify the presence of micropenis in neonatal examination to avoid delay in diagnosis of these serious, sometime life-threatening conditions. Vol. 64, No. 1, March 2019

Original article
The normal stretched penile lengths (SPL) of newborns vary depending on the maturity, ethnicity, and race [6][7][8]. Normative data used in Caucasian populations may not be applicable to Asian populations [9,10]. It is therefore important to establish normal values for SPL for Sri Lankan new-borns.

Study group
This was a cross sectional observational study, carried out in the post-natal wards of the Castle Street Hospital for Women, Sri Lanka. The study was done on 369, stable new-borns delivered at the gestational age of 37 to 42 weeks.

Exclusion and inclusion criteria
All the term healthy new-borns delivered by healthy mothers were included. Neonates of mothers with endocrine disorders or on long term medications other than usual antenatal supplements, neonates with gross congenital malformations, sick unstable neonates, small for gestational age babies (birth weight less than 2500g), large for gestational age babies (birth weight more than 3500g) and preterm babies with gestational maturity less than 36 weeks were excluded from the study.

Method of data collection
A complete neonatal examination was performed by the principal investigator and the anthropometric measurements were obtained. Weight was measured with a digital weighing scale and length was measured with an infantometer [6]. Head circumference was measured according to standard protocols, with the standard tape, and three recordings were taken, and the highest value was documented.
Stretched penile length was measured from base of the penis from pubic symphysis to the tip of the glans. Pubic fat pad was maximally depressed when taking the measurement. Tip of the glans was identified by palpation. Measurements were taken with a wooden spatula, which was kept at right angles to the symphysis pubis and the penis was stretched gently to its maximum resistance and measurements were taken along the dorsal aspect of the penis. Two measurements were taken by the principal investigator to nearest millimetre and the mean was calculated [6,7].
Gestational maturity was calculated from the first date of last regular menstruation or by the dating scan done at 11 to 16 weeks of gestation.
Data was gathered during hospital stay following the delivery after obtaining informed, written consent.
Ethical approval to conduct the study was obtained from the ethical review committee of the Sri Lanka College of Paediatricians.

Method of data analysis
Final analysis was done by SPSS statistical software. Mean penile length and statistically significant difference of penile length (SD) values were calculated. In analysis of data mean penile length, period of gestation, birth weight and length were considered. Continuous variables were expressed as mean +/-2 SD.

Results
Three hundred and sixty-nine new-borns were studied between gestational age 36 weeks to 41weeks ( Table 1). The correlation analysis of SPL with anthropometric measurements (birth weight, length and OFC) and gestational age (GA) showed there is a statistically significant positive correlation only with the length (Pearson r = 0.134, p= 0.01) (Figure 1).
The mean SPL of total sample of 369 neonates was 3.03cm, with a standard deviation (SD) of 0.38cm. There were 329 new-borns who did not have any associated maternal, antenatal or neonatal complications (excluding endocrine related disorders in the mother and neonate). Table 2 shows the comparison of mean SFL values with current study value with recent studies conducted in different countries representing Asia, Africa and Europe. All studies shows significantly higher mean values compared with Sri Lankan mean value including South Indian study [7] other than Japan [12] which is from the same region.

Discussion
Micropenis is an important parameter to identify certain endocrine disorders like pan-hypopituitarism and hypo gonadotrophic hypogonadism [5,6]. The definition of micropenis is debatable. In a term infant with normal external and internal genitalia, stretched penile length less than -2.5 SD is defined as micropenis [3,9,13]. In many recent studies, it was suggested to define micropenis as -2 SD or 3 rd percentile, in the same way as the definition of short stature [3,[14][15][16]. Measurement of penile length also varied according to room temperature, erect or flaccid penis and interpersonal measurement variability [6,17]. In this study stretched penile length was measured at room temperature (as the wards are not air-conditioned), demonstrating a relatively narrow range of variation due to the tropical climate. Two measurements of SPL were taken and the mean of the two values were taken for the analysis, while all the measurements were taken by the same investigator to avoid interpersonal measurement variability. There were 3 South Indian studies which showed a greater discrepancy in SPL of South Indian new borns as 2.31 ± 0.61 cm, 2.83 ± 0.49 cm and 3.57 ± 0.46 cm, which might be due to intra personal measurement variation and the influences of environmental factors [3,13,14].
According to this study, SPL of Sri Lankan neonates was 3.03 ± 0.37 cm, which is compatible with other Asian studies, such as 2.83 cm ± 0.49 cm in Tamil Nadu (7) and 3.00 ± 0.4 cm reported from China [18]. The Asian SPL measurements considered as being shorter than Caucasian and African measurements are also compatible with the findings of this study [6,12,14,18].
In our study, new-borns with Small for Gestational Age (SGA), Large for Gestational Age (LGA), Pre-maturity, congenital anomalies and maternal endocrine disorders were excluded. The correlation analysis of SPL with anthropometric measurements of birth weight, length and OFC and gestational age (GA) showed there is no statistically significant correlation with birth weight, POA and OFC. The only statistically significant positive correlation with the length (Pearson r = 0.134, p= 0.01) is compatible with established data. Fok et al reported statistically significant positive correlation with length and SPL, while Kutlu et al found statistically significant positive correlation of SPL with the length, weight and head circumference [6,18].
In conclusion, the findings from our study conform with the recent suggestions for the definition of micropenis to be a SPL below the 3 rd percentile or -2SD, similar to the definition of short stature. SPL positively correlates with the length of the baby. This is the first study of the SPL of new-borns from Sri Lanka. According to this study, the mean SPL for the Sri Lankan new-born is 3.03cm ± 0.37cm, and since the -2SD measurement of SPL is 2.29cm, a length less than this value should be considered as micropenis.