To evaluate the sex difference in fetal behavior between male and female fetuses.Fetal behavior was assesed by Kurjak’s antenatal neurodevelopmental test (KANET) using four-dimensional (4D) ultrasound between 28 and 39 weeks of gestation. Fifty-nine male and 53 female fetuses in middle- and high-class nulliparaous Japanese women were studied. The total value of the KANET score and values of each parameter (eight parameters) were compared.The total KANET score was normal in both groups, and there was no significant difference in the total KANET score. When individual KANET parameters were compared, no significant differences were noted in all eight parameters.Our results show that there is no difference in fetal behavior between male and female fetuses in the third trimester of pregnancy. These results suggest that 4D ultrasound study examining fetal behavior does not need to consider the factor of fetal sex.
