Development of the fetal uterus between 19 and 38 weeks of gestation: in-utero ultrasonographic measurements.

In-utero assessment of the internal female genitalia is important for determination of fetal gender in fetuses with suspected genital tract anomalies. We therefore measured fetal uterine transverse width and circumference from 19 weeks of gestation until term, using transvaginal and transabdominal high-resolution ultrasound techniques in order to establish nomograms. A prospective, cross-sectional study on 180 normal singleton pregnancies was performed. Data were obtained for 140 normal fetuses. The mean +/- SD uterine width and circumference were 12.9 +/- 4.1 mm (95% confidence interval 12.1-13.7), and 40.2 +/- 12.5 mm (95% confidence interval 37.9-42.5) respectively. Uterine size as a function of gestational age was expressed by the regression equations: uterine width (mm) = 12.9 + 0.7 x gestational age (weeks), and uterine circumference (mm) = 40.2 + 2.1 x gestational age. The correlation coefficients, r = 0.885 and r = 0.888, for uterine width and circumference, by gestational age respectively, were highly statistically significant (P < 0.001). A nomogram of uterine width and circumference per gestational week, and the 95% prediction limits were defined. The present data offer baseline measurements of the fetal uterus that may allow intrauterine assessment of the female genital tract and associated fetal gender.