Amniotic fluid testosterone in the prenatal determination of fetal sex

In the field of genetics, a rapid and accurate test for the prenatal determination of fetal sex, especially in cases of sex-linked disorders, is desirable. Amniotic fluid testosterone was measured by the radioimmunoassay technique in 37 samples obtained at saline abortion between 16 and 19 weeks' gestation. Final confirmation of fetal sex was obtained from fetal gonadal histology. In pregnancies with male fetuses, the mean amniotic fluid testosterone value of 27.6 ng. per 100 ml. was significantly higher (p less than 0.001) than the mean value of 9.6 ng. per 100 ml. found in pregnancies with female fetuses. The range for pregnancies with male fetuses was 15.5 to 41.3 ng. per 100 ml. and for those with female fetuses 5.7 to 15.1 ng. per 100 ml. With a coefficient of variation of 5 to 8% considered for the method of assay, there was an area of potential overlap from 12 to 18 ng. per 100 ml., giving a predictive error of approximately 16%. For patients in whom the results are clearly outside the area of overlap, this test is of value as a preliminary screen in the prenatal determination of fetal sex, especially in X-linked disorders.