Why Are There More Boys Than Girls? Hint: It's Not Super Sperm!

Boys outnumber girls, but I bet you can't guess why. We did the research for you!

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  By: Tali Ditye, Ph.D., Co-founder

  Updated: April 28, 2023

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Since the 1800's, scientists have wondered why so many more male babies were born than female babies.

Last year alone, in the United States there were 3.2 million more boys than girls (source).

And there are tons of possible explanations why boys are so much more common.

It could be something happening with the sperm, with the egg, something having to do with super sperm fiercely swimming at never-before-seen rates (my husband prefers this explanation), something to do with implantation odds, the embryo, different miscarraige rates for boys and girls, and more.

My husband prefers to think that his Super Sperm caused us to have four boys.

The rate of boy versus girl births is consistently about 51% boys and 49% girls. Given that there are about 4 million childbirths per year in the USA, that means about 40,000 more boys than girls are born each year.

Why More Baby Boys than Girls?

Some recent research sheds some light on this discrepancy.

Scientists from Harvard Medical School examined the chromosomes (X or Y) from sperm all the way to baby birth. They studied sperm, eggs, about 140,000 embryos, data from nearly 1 million amniocenteses, and analyzed the outcomes of over 30 million abortions, miscarriages, and births.

Here's what they found:

At the stages of sperm, egg, sperm/egg interaction, embryo and implantation, there is a perfectly 50/50 split between boys and girls. That means that until your baby is already implanted in the wall of the uterus, there is no bias toward boy or girl.

From sperm to implantation, the odds are perfectly 50/50 boy or girl.

So what's going on exactly?

Well, it turns out that a few things are happening after implantation.

First, more male fetuses are dying during the first week of pregnancy, likely due to chromosomal abnormalities.

But after that first week, the rates of female fetuses miscarrying is higher than the rate of male fetuses miscarrying. This is especially true in the second trimester and third trimester. And that rate is so much higher that it over-compensates for that increased mortality of male fetuses during the first week.

Plenty of fish in the sea, for girls!

So there you have it. You can tell your husband it probably had nothing to do with how strong his "swimmers" were, or that secret sex position you tried while ovulating.

Instead, it's all about carrying more boys than girls to term. And that's a fact.

Trying to pick a baby name or help people figure out whether to buy baby gifts for a girl or boy? before discovering your baby's sex? Check out our huge list of gender-neutral baby names!