Diagrammatic representation of the embryological process of labio-scrotal fusion.  The male fetus is shown indistinguishable for the female fetus during the 10th-12th week of gestation.  As labio-scrotal fusion occurs, the male fetus becomes increasingly identifiable as male and at the same time becoming distinguishable from the female.  This process occurs during the 12th-14th week of gestational Age.  The reported attainment of essentially 100% accuracy of F.A.S.A. becomes achievable from the 12th week of gestational age and beyond.  LM-labio-scrotal fold:  TS-testicular sac:  P-penis:  C-clitoris:  GT-genital tubercle.

This is a schematic diagram of the accompanying Polaroid film images of the typical image showing prominent male and female genitalia patterns as imaged in scan plane #1.  The Polaroid film documentations were obtained from fetuses in the 12th week of gestation. 
TS-testicle sac:  P-penis:  C-clitoris:  LM-labia majora.

This is a schematic diagram of the accompanying Polaroid file images of the typical scans which show prominent male and female genitlia patterns as imaged in scan plan #2.  The Polaroid film documentations were obtained from fetuses in the 12th week of gestation. 
TS-testicle sac:  P-penis:  C-Clitoris.

This shows unconventional transducer placements on the maternal abdomen used to image a male fetus between the thighs as seen in scan plane orientation #1 and to image the fetus sagittaly through the longitudianal axis of the fetal body to obtain scan plane orientation #2.