During assisted reproduction treatment, questions may arise about what information can be obtained from embryos before transfer. One of these is whether it is possible to know whether the future baby will be a boy or a girl and, above all, whether it is possible to choose.
Currently, some embryo genetic testing techniques make it possible to know their sex chromosomes. However, in Spain, sex selection is regulated and cannot be performed for personal or family preferences. Its use is reserved for specific medical situations, such as the prevention of serious genetic diseases.
What determines the baby’s chromosomal sex?
Chromosomal sex is determined at the moment of fertilisation when the egg and the sperm unite.
The egg always contributes an X chromosome, while the sperm may contribute either an X chromosome or a Y chromosome. The XX combination is usually associated with female sex, and the XY combination with male sex.
Therefore, it is the chromosome contributed by the sperm that determines the chromosomal sex of the embryo.
Can the sex of embryos be known during IVF?
In certain in vitro fertilisation treatments, preimplantation genetic diagnosis (PGD) may be indicated. This technique makes it possible to analyse specific genetic characteristics of embryos before transfer.
Some types of PGD also provide information about the embryo’s sex chromosomes, and make it possible to determine whether it has an XX or XY combination. However, having this information does not mean that it can be used to choose which embryo to transfer according to its sex.
Can you choose whether the baby will be a boy or a girl in Spain?
Law 14/2006 on assisted human reproduction techniques does not allow the sex of embryos to be selected for personal or family preferences.
Therefore, it is not possible to choose an XX or XY embryo simply because of a desire to have a boy or a girl, or to seek a certain family balance.
However, the legislation does provide for certain medical situations in which genetic testing of embryos may be used to avoid the transmission of a serious hereditary disease.
When may embryo selection according to sex be indicated?
Some hereditary diseases are linked to the sex chromosomes, especially the X chromosome. In these cases, genetic testing of embryos may form part of the strategy to reduce the risk of transmitting the disease to offspring.
Today, PGD makes it possible to directly study many specific genetic alterations. In this way, in certain cases it is possible to identify embryos that do not carry the alteration being studied, rather than selecting them solely based on their sex chromosomes.
The strategy will depend on the disease, its mode of transmission and the family history. In addition, some tests require specific authorisation from the health authority and a favourable assessment by the National Commission on Assisted Human Reproduction. For this reason, each case must be studied individually before starting treatment.
Do natural methods for choosing the baby’s sex work?
There are different theories linking the timing of sexual intercourse with a higher probability of conceiving a boy or a girl. The best known include the Shettles and Whelan methods, which are based on scheduling intercourse on specific days of the menstrual cycle.
However, these methods have not been shown to be effective in selecting the sex of the future baby. Nor are there dietary guidelines, sexual positions or lifestyle changes that allow it to be chosen reliably.
Frequently asked questions
Can the sex of the baby be chosen through IVF?
In Spain, it is not permitted to choose the sex of the future baby for personal or family preferences. The study of embryos’ sex chromosomes is reserved for specific medical indications.
Does PGD make it possible to know whether an embryo is XX or XY?
Some types of PGD can provide information about the embryo’s sex chromosomes. However, this information cannot be used in Spain to select which embryo to transfer solely because of the desire to have a boy or a girl.
Can sex be selected to avoid a genetic disease?
In certain serious genetic diseases linked to the sex chromosomes, it may be necessary to study this information. In many cases, PGD makes it possible to directly analyse the genetic alteration responsible for the disease to identify embryos that do not carry it.
