Accuracy of fetal gender determination in the first trimester using three-dimensional ultrasound

Ultrasound Obstet Gynecol. 2011 May;37(5):557-61. doi: 10.1002/uog.8812. Epub 2011 Mar 2.


Objectives: To evaluate the accuracy of three-dimensional (3D) ultrasound in fetal gender assignment in the first trimester.

Methods: A series of pregnant women attending at 11 to 13 + 6 weeks for the nuchal translucency (NT) scan were enrolled into the study. An ultrasound volume of each fetus was obtained and stored for offline analysis. On the reconstructed mid-sagittal plane, the angle between the genital tubercle and an imaginary line passing tangentially through the fetal back (genital angle) was estimated and a receiver-operating characteristics (ROC) curve was constructed to determine the best cut-off for genital angle in fetal male gender determination. Fetal gender was subsequently ascertained in all cases. To calculate the interobserver variability, a second operator repeated the measurements.

Results: There were 85 cases included in the study. The genital angle in males was significantly higher than that in females (51.2 ± 11.3° (n = 36) vs. 18.9 ± 4.1 (n = 49), P < 0.001). The ROC curve revealed the estimated genital angle to have a high degree of accuracy in fetal gender determination (area under the curve ± SE = 1.000 ± 0.001). The best cut-off for male gender determination was found to be between 27° and 29° (sensitivity, 100%; specificity, 98.0%). There was a high degree of correlation between the two operators (r(2) = 0.998; coefficient of variation = 5.4%).

Conclusions: 3D ultrasound is a highly accurate and reproducible tool for fetal gender assignment prior to 14 weeks of gestation.

Publication types

  • Evaluation Study

MeSH terms

  • Adult
  • Area Under Curve
  • Female
  • Genitalia, Female / diagnostic imaging*
  • Genitalia, Female / embryology
  • Genitalia, Male / diagnostic imaging*
  • Genitalia, Male / embryology
  • Humans
  • Imaging, Three-Dimensional / methods*
  • Male
  • Middle Aged
  • Observer Variation
  • Predictive Value of Tests
  • Pregnancy
  • Pregnancy Trimester, First
  • ROC Curve
  • Reproducibility of Results
  • Sex Determination Analysis / methods
  • Ultrasonography, Prenatal / methods
  • Young Adult