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Fetal phallic growth and penile standards for newborn male infants

K W Feldman, D W Smith

    The Journal of Pediatrics
    |March 1, 1975
    PubMed

    Insights

    Fetal external genitalia size differences emerge after 14 weeks gestation. Penile growth accelerates significantly in the second trimester, continuing linearly until birth.

    Area of Science:

    • Prenatal development
    • Fetal anatomy
    • Embryology

    Background:

    • External genitalia in fetuses are initially similar in appearance.
    • Masculine differentiation of external genitalia occurs early in gestation.

    Purpose of the Study:

    • To investigate the timing of size differences between fetal penises and clitorises.
    • To characterize the growth rates of external genitalia during the second trimester.
    • To establish normative measurements for full-term infant penile size.

    Main Methods:

    • Comparative analysis of fetal external genitalia size.
    • Longitudinal assessment of growth rates during the second trimester.
    • Measurement of penile length and diameter in full-term infants.

    Main Results:

    • No significant size difference between clitoris and penis before 14 weeks gestation.
    • Accelerated and linear growth observed in penile size after 14 weeks gestation.
    • Full-term infant penile dimensions: 3.5 cm (length) ± 0.7 cm and 1.1 cm (diameter) ± 0.2 cm.

    Conclusions:

    • Sexual dimorphism in external genitalia size becomes apparent after 14 weeks gestation.
    • Penile growth follows a distinct, rapid trajectory in the second and third trimesters.
    • Established penile measurements provide a reference for neonatal assessment.

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