How to Conceive a Boy or a Girl (According to Science)

As someone who never found out the sex of my babies until they joined us on the outside, I’m not sure I fully understand our fascination with the sex of unborn babies. We even have gender reveal parties (which—ahem—should be assigned-sex-reveal parties) so elaborate that they cause acres of wildfire damage.

Total strangers would stop me on the street to say things like 'Oh wow, you're carrying low; that's definitely a boy.'

During my pregnancies, total strangers would stop me on the street to say things like “Oh wow, you're carrying low; that's definitely a boy.” Hmm. I’m pretty sure the low-hanging belly just means I had no ab muscles to speak of when we started on this pregnancy journey, so the muscles that were there just gave up.

But what does fascinate me is whether or not there's any scientific evidence to back up the common lore surrounding how women might influence the sex of their baby. I’ve heard many times that eating a lot of salty snacks and red meat while you’re trying to conceive will produce a boy. Or, if you have a lot of chocolate and yogurt in your diet when you get pregnant—and who doesn’t?—you’re destined to have a girl.

Sometimes advice like this gets passed along without any backing, but sometimes it’s based on convincing anecdotal data. 

How is a baby's sex determined?

The sex of a fetus is determined by its X and Y sex chromosomes. Very simply put, the provider of the egg typically also provides an X chromosome while the sperm can either contribute another X chromosome or a Y chromosome. Two X chromosomes (XX) make a girl, and an X and Y (XY) chromosome combined make a boy. There are rare instances when a sperm may have both an XY which creates a boy with Klinefelter syndrome (an XXY boy) or no sex chromosome to create a girl with Turner syndrome (an X girl). 

Two X chromosomes (XX) make a girl, and an X and Y (XY) chromosome combined make a boy.

There are ways to use technology to essentially choose the sex of the baby. An embryo with a known sex can be implanted through in vitro fertilization (IVF) via a process called pre-implantation genetic diagnosis. 

Sperm can also be sorted into X and Y carriers before being used in artificial insemination. One such sperm sorting technology, called ...

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