Often, the reason a family wants to select the sex of their child is for a medical reason. This could be because the family is genetically predisposed to passing on a sex-linked genetic disease, many of which are inherited by the mother but only affect her male children.
Examples of sex-linked genetic diseases include muscular dystrophy, fragile-X syndrome and hemophilia. Nearly all people with sex-linked disorders are male, and the disorder is passed on through the mother because a son’s X chromosomes always come from the mother. All daughters of an affected male will be carriers.
Families who want to screen embryos for the single gene mutations that cause genetic disease can do so by undergoing in vitro fertilization (IVF) and having the resultant embryos tested with single-gene preimplantation genetic diagnosis (PGD), which looks for a single specific mutation. However, if the genetic disorder is sex-linked, a couple may also simply choose to screen for the sex chromosome with preimplantation genetic screening (PGS). PGS does not look for a specific disease and instead screens chromosomes for abnormalities and sex. With PGS, the fertility doctor can select only female embryos to transfer to the woman’s uterus.
Another medical reason for selecting the gender of a baby may, in fact, be psychological. For example, a family may have lost a child and wants to have another child of the same gender.