Normal growth and development of fetal external genitalia demonstrated by sonography

Our aim in this retrospective sonographic study was to describe the normal growth and development of fetal external genitalia.

We reviewed the sonograms of anatomically normally fetuses, obtained over a 5-year period, and measured transverse scrotal diameter or penile length in male fetuses and bilabial diameter in female fetuses. Transverse scrotal diameter was measured from the midpoint of the lateral scrotal wall to the midpoint of the opposite lateral wall; penile length, from the base of the shaft to the tip; and bilabial diameter, from the midpoint of the lateral labial margin to the midpoint of the opposite lateral labial margin.

We examined sonograms from 1,182 fetuses and measured transverse scrotal diameter in 304 and penile length in 494 male fetuses and bilabial diameter in 384 female fetuses. The fetuses ranged from 14 to 41 weeks' menstrual age. Transverse scrotal diameter, penile length, and bilabial measurements were highly correlated with menstrual age (r = 0.941, r = 0.860, and r = 0.898, respectively). We found that growth of fetal external genitalia is similar to that for other parameters of fetal growth, such as biparietal diameter and femur length.

The results of this study may be helpful in understanding the natural course of the growth and development of fetal external genitalia. In addition, the data we gathered may be useful in combination with other biometric data for estimating fetal age and may help in detecting abnormalities in the fetal external genitalia.