Distribution by sex of mouse fetuses in the intrauterine position

We examined whether or not the sex of the fetuses of polytocous animals distributes randomly in the position along the uterine horn in 255 mouse litters. The fetal sex ratio did not differ significantly among the three intrauterine segments (ovarian, middle, and cervical). Based on the number of fetuses examined in this study, it can be stated that even if sex ratio differences exist among the segments, the ratio in individual segments would fall mostly inside the +/- 0.1 range, when the overall sex ratio (M/(M + F] is around 0.5.