Boy or Girl

There are 46 chromosomes that carry the complete human genetic blueprint and the sex of your baby is determined by just two of them: the X and the Y.

A women’s egg contains a single X chromosome and a man’s sperm can contain either an X or a Y chromosome. If a sperm carries an X chromosome (XX) the baby will be a girl, and if it carries a Y (XY) chromosome the baby will be a boy. This means that your partner’s sperm determines the sex of your child, rather than your egg (so you know who to blame when you find out you are expecting your fifth boy!) Y sperm swim faster but are smaller and don’t live as long as X sperm.

There are plenty of folk legends which suggest, among other things, that women should sleep with meat under their mattress for a boy or tie a pink ribbon onto their bed for a girl – but needless to say, none of these actually work. Changing your diet has also been rumored to affect whether you conceive a boy or a girl because eating acidic foods, such as citrus fruit, is thought to affect vaginal secretions in a way that makes them more favorable to Y sperm (boys); while eating alkaline foods, such as dairy produce, is supposed to produce conditions that favor X sperm (girls).

Another theory is that you can influence your baby’s gender by timing sex. Sperm carrying the Y chromosome swim faster but die sooner and sperm carrying the X chromosome last longer but can't swim as fast. This means that if you have sex before you ovulate, the boy sperm may swim faster but won't be able to hang around for the egg, but the girl sperm will amble more slowly but survive long enough to hit the jackpot! So work out when you ovulate with our ovulation calculator, then either have frequent sex on the days leading up to ovulation for a girl, or on the exact day or the day after for a boy... of course, this is just a theory, but there's no harm in trying!

Let us know your thoughts on influencing the sex of your baby by posting a comment on the chat pages. Also, tell us any old wives’ tales you have heard of, or if you think you had an influence on your baby’s gender.

The information in this feature is intended for educational purposes only. If you have any concerns about your health, the health of your child or the health of someone you know, please consult with a doctor or other healthcare professional.

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Last Modified: 26/04/2007

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