Sex ratio of hamster fetuses assessed by gonadal morphology: effect of mother's age.

This paper describes the assessment of phenotypic sex in hamster fetuses 12-15 days postcoitum. External morphometric parameters such as body weight, crown-rump length and anus-genital distance did not permit the differentiation of males from females. The sex was determined easily by inspection of the internal genital structures under low power magnification on Days 13-15 postcoitum. The size, shape and location of the gonads and the presence of a conspicuous blood vessel on the testis were the most useful criteria. An inverse relationship was found between the age of the mother at conception and the number of fetuses in mothers 2 to 7 months old. The decrease in the number of fetuses with increasing age of the mothers affected preferentially the population of phenotypic males.