As Dr. Elena Trukhacheva, president and medical director of the Chicago-based Reproductive Medicine Institute, explains, once embryos are created in vitro, they are sometimes screened in order to choose the healthiest ones to implant into the mother's womb. Called Preimplantation Genetic Diagnosis (PGD), it's a complete chromosomal analysis of each embryo.
Trukhacheva says that if screening indicates that there are healthy embryos of both genders, about half of patients ask to choose the gender to the implant. Trukhacheva doesn't have an ethical issue with gender selection at this stage, particularly because she has not seen a pattern of discrimination against one gender. "It's usually an issue of balance, that the couple has two boys and would like a girl, or vice versa."