How a Babys Sex Is Determined

What determines a baby’s sex? Every time a woman gets pregnant, there is a 50% chance the baby will be a boy and a 50% chance of the baby being a girl. It is all up to the single male sperm that fertilizes the egg.

Normal cells have 46 chromosomes (23 pairs). These chromosomes are the packaging for DNA (deoxyribonucleic acid). DNA is the hereditary genetic material that gives our bodies instructions on how to grow and develop. DNA is organized into units called genes.  When a woman makes an egg, it has 22 autosomes (chromosomes that are not sex chromosomes and appear in matched pairs) and one X chromosome. When a man makes a sperm, it has 22 autosomes and one X chromosome (would create a female) or one Y chromosome (would create a male).

When the sperm fertilizes the egg, the majority of the time, the two fuse to create an embryo with a complete set of 46 chromosomes. If the embryo’s sex chromosome is an XX, the embryo is a female; if it is an XY, the embryo is a male. In some cases, there are chromosomal abnormalities, such as XXX, XYY, XXY (Klinefelter Syndrome) and X0 (Turner Syndrome).

Some natural methods of trying to influence a baby’s gender — as well as some scientific methods — work from the theory that Y-bearing sperm are faster, lighter and more fragile than X-bearing sperm. The Y-bearing sperm has less DNA than the X-bearing sperm because the Y chromosome is much smaller than the X. The only real function of the Y chromosome is to eventually turn a fetus into a fertile male, while the X chromosome has thousands of genes.