It is possible to determine the gender of a future baby (embryo) before transfer takes place. In fact, this strategy has been used for many years in order to avoid the transmission of sex chromosome hereditary diseases (pre-implantation genetic diagnosis or PGD).
When the technique was in its early days, embryo analysis was carried out on day 3 of embryo development. Nowadays, it is carried out between days 5 and 7 of development (blastocyst stage). The analysis provides a simultaneous understanding of all the chromosomes in the embryo, meaning that transmission of chromosomal abnormalities can be completely eliminated. The technique has a 98% success rate.