Will I Have a Boy or a Girl? Predicting Your Baby’s Gender

predicting baby gender

Are you having a girl or a boy? Mathematical probability says it’s close to an even chance of either (with slightly more chance of a girl baby) even if you think boys or girls run in your family. Image by Alan Reeves

When you’re pregnant, you may find yourself wondering if you’re carrying a boy or a girl as you wait for that all-important ultrasound date. You can search online for a “Chinese baby gender predictor” or a “baby gender predictor test” – some of these sites use astrology, the expectant mother’s symptoms while pregnant, or a variety of folk wisdom approaches for baby sex predictions. Those are all in good fun, but are about as accurate as flipping a coin.

What Gender Will The Baby Be? Statistics, Math, and Probability

Without filtering statistical results from a reliable set of tests, it seems safest to make one of two assumptions: Either each baby has an independent chance of being a boy or girl, or some factor skews the chances for some couples.

Let’s discuss the equal opportunity baby gender predictor. The mother’s gender gene is ‘XX‘; the father’s is ‘XY‘. Their child will either inherit the father’s ‘X’ or ‘Y’ allele. In theory, this should result in a 50% chance of either gender in every pregnancy. This suggests that if each conception is statistically independent, your next baby has an equal chance of being a boy or girl. It’s like flipping a fair coin, where a string of “heads” does not make the next toss more likely to be “tails.”

Whether there is something different about sperm carrying the ‘X’ versus ‘Y’ allele or not, we know it’s not an exact coin flip, since in practice, pregnant mothers conceive slightly more girls than boys. Some web sites offer advice for influencing your baby’s gender before conception, but any scientific explanation for the baby’s gender would be due to a difference between sperm carrying ‘X’ or ‘Y’ alleles, rather than what you’re supposed to do that may affect that sperm’s chance of success.

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  1. I wonder, if I had known in advance, would it have changed anything? Hmmmm. Thanks for the explanations here.


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