How Can I Conceive a Girl?

My mum is very convinced that there’s lots you can do to make sure you “make” a girl baby when you conceive, including having sex early before ovulation. Is there any truth to this?
—Mum of Two Boys

This is a very, very enduring myth. It’s sometimes called the Shettles method — the idea is that you want to have sex early before ovulation to get a girl, because girl-producing sperm are slower swimmers but have more endurance. It’s like elite athletes! But in sperm form.

However, the lessons from endurance running do not seem to apply to sperm. The best evidence we have on this is from a 1995 paper in which the authors followed couples trying to get pregnant, had them report the timing of intercourse, and then connected the timing to the child’s sex. They did not find any link. And honestly, there is really no reason to think there would be one.

Why does this myth endure? I think it’s because it’s easy to find anecdotal evidence. Half the time, it will work! Because the baseline chance of having a girl is about 50% (actually it’s about 49.5%, since more boys are born overall, but anyway). And people remember their successes more than their failures.

I am sorry to say your mum is wrong here.