Introduction: Fetal ultrasound-based measurements such as penile length, width, and anogenital distance currently lack specificity for diagnosing genitourinary pathology. Furthermore, there is a lack of standardization in measurement techniques and evaluation across centers in normative values by gestational week. This systematic review aimed to 1) investigate the variability in external fetal genitalia sonographic measurement methods and 2) establish normative values and growth curves for these measurements.
Methods: A literature review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Three sources of information were searched: PubMed, Google Scholar, and Web of Science. All results were screened by at least two reviewers (NV, IG, and AG), and disagreements were settled by NV and RS. Primary inclusion criteria were studies reporting sonographic fetal penile length, width, and/or anogenital distance measurements by gestational age. Exclusion criteria included studies examining genitourinary abnormalities, intrauterine growth restriction, and magnetic resonance imaging. Case reports, reviews, commentaries, and non-English studies were excluded. All measurements were grouped by measurement location (e.g., cavernosal vs penoscrotal length). Data was standardized to the mean (mm) and 95% confidence interval, then plotted over gestational age.
Results: Our search criteria yielded 173 articles, of which 17 were included. Variability in techniques included axes and anatomic landmarks. Five (29%) provided postnatal outcomes. Eight evaluated fetal penile length from the scrotum to the tip of the penis, 6 penile width, and 3 anogenital distance. Six of the 8 studies evaluating penoscrotal penile length provided data by gestational week for analysis. The mean penile length was plotted versus gestational age to provide a normative growth curve (Figure 1). The plot established a reference for the overall mean (± 95% CI) penile length using all studies that reported weekly measurements, with an anticipated normal growth curve represented by the equation y = 0.8068x - 8.8388 (Figure 2).
Conclusions: Based on published data, the resultant growth curves from this review will provide a valuable reference for clinicians assessing penile length, width, and anogenital distance in fetal ultrasounds, facilitating comparison to normative measurements by gestational age. Future collaborative efforts are needed to establish standardized measurement approaches and to evaluate the predictive value of sonographic findings for suspected micropenis, hypospadias, or other genital developmental differences.
