in drosophila, the sex is determined by (a) the ratio of pairs of x-chromosomes to the pairs of autosomes asked oct 27, 2018 in biology by richa ( 60.). Although sonographic fetal sex determination is feasible in most pregnancies, in some cases, it may pose difficulties. An attempt to determine the fetal sex should not be made before 12-weeks gestation because this early, it is relatively inaccurate. Fetal sex could be determined in 75 per cent of the male infants and in 73 per cent of the females. The wrong sex was determined in 3 per cent of all examinations. In 25 and 21 per cent of female and male fetuses respectively sex determination could not be accomplished. in girls, development of external sex organs remains pretty much static over time. By about week 20 of pregnancy, your baby girl will have 7 million primitive eggs, which will pare down to about 2 million by the time shes born. 01 nova the sex of an egg cell is set as soon as it is fertilized, but what happens to that cell and the cells it divides into to make a baby. Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. Sexual differentiation includes development of different genitalia and the internal genital tracts and body hair plays a role in gender identification. Prenatal sex discernment can be performed by preimplantation genetic diagnosis before conception, but this method may not always be classified as prenatal sex discernment because its performed even before implantation. Cell-free fetal dna testing, wherein a venipuncture is performed on the mother to analyze the small amount of fetal dna that can be found within it. They repeated this process again in the second trimester between weeks 18 and 24, when babys sex can also be determined via ultrasound. By this point, only 477 women still met their study criteria. possible gender-specific effect of teratogens is not always established because in most studies embryonic and fetal genetic sex is not determined. The paucity of data relating teratogenic effects to gender seems to result from the difficulties in the accurate anatomical assessment of sex in fetuses or newborns. There is a recent discovery of the presence of fetal generic material in a maternal blood, and it offered new approaches and methods to non-invasive diagnosis. This blood test can detect down syndrome and other chromosomal disorder at the 10th week of pregnancy, and even later. Cell-free fetal dna originated from trophoblasts making the placenta.