Evaluating Male Fetal External Genital Morphology: A Systematic Review of Sonographic Techniques and Normative Values

Although commonly evaluated, fetal ultrasound assessments of penile length, width, and anogenital distance (AGD) lack standardized measurement techniques. This systematic review aimed to evaluate variability in measurement methods and generate normative growth curves for externally virilized genital development. Following PRISMA guidelines, PubMed, Google Scholar, and Web of Science were searched for studies reporting sonographic measurements of fetal penile length, width, or AGD by gestational age. Exclusion criteria included abnormal genitourinary development, intrauterine growth restriction, non-ultrasound imaging modalities, and non-English publications. Manuscripts were analyzed by a minimum of three reviewers. Data were standardized to mean dimensions and 95% confidence intervals by gestational week. Nine studies met inclusion criteria. Six measured penile length (scrotum to tip), four measured width (widest penile region), and three evaluated AGD (scrotum to anus). Resulting regression equations were y = 0.7862x - 8.4627 (length), y = 0.4209x - 3.1445 (width), and y = 1.0129x - 11.239 (AGD). Quality assessments revealed only 51.97 ± 21.5% of study parameters had a low risk of bias. The resultant growth curves provide a reference for normative development. Standardized assessment protocols and studies of anomalous development are needed to improve measurement consistency and assess the predictive value of these findings.