Normally, you would leave the gender selection in the case of your baby in the hands of God since after all both the genders are the children of God. But there are times and conditions when you are either helpless or would like to opt for the selection of a specific gender for your baby due to some specific reasons. These are extreme conditions when you could opt for your preference of the baby gender.
The first reason or set of reasons for opting for gender selection could be physiological or medical. There could be a medical condition when one of you could have a genetic mutation that is gender specific. It has been found that certain genetic disorders could be the result of a genetic mutation of the X-chromosome that's a sex chromosome. If you, the mother have this mutated X-chromosome then you or your daughter to be would not be affected but there is a definite possibility that your son to be could be afflicted with this disease. You and your partner in such a case could opt for the female baby gender. In such a case only the female embryos would be selected for transfer. There's a similar case with the male's Y-linked mutation as well.
Carrying out prenatal tests during pregnancy can quite easily indicate the baby gender. But this might lead to an unnecessary termination of pregnancy or you could be faced with the unhappy prospect of bringing into this world a child with a deformity. Gender selection therefore needs to be carried out in advance. Sometimes it might become necessary to have a balanced family and you may like to be able to select the right gender of your baby so that you could have equal number of male and female offspring. There are cases of families with large number of only boys or only girls. In such cases also the selection of the gender is an option that you may exercise. There are methods available these days to be able to select the gender of your baby with a fairly high degree of accuracy.