Precision and reliability of anthropometric measurements of the male external genitalia in neonates. A comparison between penile length, width, anogenital and anoscrotal distance in a large birth cohort
Rodrigo LP Romao, MD1, Linda Dodds, PhD1, Jillian Ashley-Martin, PhD1, Patricia Monnier, MD, PhD2, Tye Arbuckle, PhD3.
1IWK Health Centre, Dalhousie University, Halifax, NS, Canada, 2Research Institute of the McGill University Health Centre (MUHC), MUHC Reproductive Centre, Montreal, QC, Canada, 3Health Canada, Ottawa, ON, Canada.
Background: Penile length (PL), width (PW), anogenital distance (AGD) and anoscrotal distance (ASD) have been studied as surrogates of adequate androgen stimulation during the masculinizing programming window. Performing such measurements reliably in neonates and young infants can be challenging. The objective of this project was to study the intra-rater reliability as well as the variability of these measurements between multiple centers participating in a large pan-Canadian birth cohort study; secondarily we also analyzed the correlation between the 4 variables in full term neonates.
Methods: Prospective cohort using data collected by the MIREC-ID (Maternal-Infant Research on Environmental Chemicals – infant development) study. 215 male neonates underwent a physical exam in 5 Canadian centers as a follow-up to a cohort study that measured the levels of environmental chemicals in 2001 pregnant women. PL, PW, AGD and ASD were measured 3 times by the same trained practitioner soon after birth in 5 centers. All research personnel received standardized training on performing the measurements before recruitment started. Descriptive statistics were calculated for each variable. Intra-class coefficients were computed to evaluate intra-rater reliability between repeated measurements of the same variable. Analysis of variance (ANOVA) was performed to compare means of individual measurements across centers after confirming homogeneity of variances using Levene's test. A composite measure of PL, PW, AGD and ASD was calculated as the mean of the 3 measurements for each subject and compared between centers. Finally, correlation between the 4 anthropometric measurements was tested by calculating correlation (Pearson) coefficients.
Results: Complete data were available for 200 neonates. Intraclass correlation coefficients confirmed excellent intra-rater reliability (ICC-PL=0.89, ICC-PW=0.80, ICC-AGD=0.84 and ICC-ASD=0.85; p<0.001 for all). The means of the 3 AGD measurements were significantly different between centers on ANOVA (p<0.001); means were comparable across centers for the 3 individual measurements of the other anthropometric variables. Mean PL, PW, AGD and ASD were 21.48±4.2, 10.4±1.9, 43.65±4.94 and 22.51±4.37 mm, respectively. The only genital anthropometric measurement that showed statistically significant correlation with the others was AGD, although the strength of the association was weak for all of them (PL – r=-0.225, PW – r=0.186 and ASD – r=0.315).
Conclusions: Penile length, width, anogenital and anoscrotal distances depicted high intra-rater reliability; repeated measurements of these anthropometric variables were comparable across 5 Canadian centers except for anogenital distance. Whether this is due to measurement inaccuracies or true variation between groups remains to be studied. Although these 4 measurements have been used as surrogates of satisfactory in utero androgen stimulation leading to adequate development of the male external genitalia, our data indicated that the correlation between them is limited.
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