Chromosomes and Gender Selection

Chromosomes determine gender.

Our gender — whether we are male or female — is determined by our chromosomes. Females have an XX pair of chromosomes, and males have an XY pair of chromosomes. When a couple conceives, there is a 50 percent chance it could be a boy and a 50 percent chance it could be a girl. The only proven, successful method for choosing the sex of your child is through preimplantation genetic screening (PGS) with in vitro fertilization (IVF).

What Are Chromosomes?

Chromosomes are like the packaging for DNA (deoxyribonucleic acid), which is the hereditary genetic material that gives the body instructions on how to grow and develop. These instructions are organized into units called genes.

Typically, there are 46 chromosomes in each of the cells of our body. These 46 chromosomes come in 23 matching pairs, with one chromosome in each pair inherited from the mother and one chromosome in each pair inherited from the father. Twenty-two of these pairs are called autosomes, and the 23rd pair is the sex chromosomes: XX or XY.

Who Determines Sex of the Baby?

In natural conception, the male partner determines the sex of the baby.

When a woman makes an egg and a man makes a sperm, the cells go through an important process of dividing the 46 chromosomes in half so that the egg contains 22 autosomes and one X chromosome, and the sperm contains 22 autosomes and one X or Y chromosome that will determine sex. Then, when an egg is fertilized by a sperm, the two fuse to create a fertilized egg with 46 chromosomes (23 pairs). The sex chromosome in the sperm determines the sex of the baby. If the sperm is carrying a Y chromosome, the baby will be male, and if the sperm is carrying an X chromosome, the baby will be female.

Can I Select the Gender of My Baby?

There is a long history of couples trying to influence the outcome of a baby's gender, whether it is via timed intercourse or other methods passed down through the years. However, the only truly accurate way to be certain of a baby's gender is to use in vitro fertilization (IVF) with preimplantation genetic screening (PGS). With IVF and PGS, the egg and sperm are fertilized in the laboratory, and then on Day 3 or Day 5, the embryo is biopsied and examined for the Y chromosome. If the Y chromosome is present, the embryo is a male.

PGS is 99.9 percent accurate in gender selection.