Determination of foetal sex by ultrasound: state of the art

Abstract

The determination of foetal gender is clinically indicated in sex-linked disorders. The reliability of ultrasound in prediction during the late second and third trimesters is well-established. Few studies attained high success rate in early second trimester. The variations in the success rate are due to the difference in size and gestational age of the published samples. Most studies have concentrated on the visualization of the external genitalia. Differentiation based on internal organs is not pursued. The ethical aspects have received attention by almost all workers in this field.

PIP: Determination of fetal gender by ultrasound may be clinically indicated to rule out sex-linked disorders or a need for amniocentesis. Although ultrasound's predictive reliability in this case varies with the presentation and position of the fetus, fetal genitalia can be visualized in over 60% of examinations performed before the 18th week of gestation and in 100% of those after week 20. Before the 18th week, differentiation is more informative when the sagittal, as opposed to the coronal or transverse, view is used. Between weeks 12-14, determination can be made on the basis of a longer anogenital length in males and its higher ratio to femoral length. After the 18th week, the transverse plane is most effective in showing the penis in cross or oblique section. Through this technique, testicular descent can be observed in about 50% of male fetuses examined at weeks 28-30. In a 24-week-old fetus, the coronal view best reveals the labia and clitoris. In males, a cross section of the umbilical cord can confound findings; thus, the cord should be viewed in longitudinal section passing between the legs in front of the genitalia. To avoid termination of a healthy fetus of unwanted gender, general practice is to withhold gender information from parents unless there is a medical indication.