Girl or boy: a fifty-fifty chance?
It seems logical, and we willingly submit to this biological coin toss. The stakes feel small compared with the anxious wait to learn that conception has happened, or that a foetus is healthy.
But that is for the first child. With the second, you may hope to complete the collection. “Oh, no, I’ve already got that one.”
The French expression le choix du roi—“the king’s choice”, meaning a boy and a girl—has survived the centuries for a reason. First a boy to pass on the name: passing names through men remains customary, though it is no longer legally automatic in France. Then a girl to cement an alliance with another powerful family through marriage: entirely obsolete.
With the third, things get complicated…
“If your first two children are the same sex, there’s a 75% chance the third will be the same sex too.”
At least, that is what people keep telling you—usually without being asked—once you have two boys or two girls.
Where does that probability come from? No idea. The rumour circulates in maternity wards, but we could find little online to confirm or refute it.
To find out, we decided to count French households ourselves. We found the 2014 INSEE census dataset. Martial, accustomed to handling millions of data points to analyse players’ behaviour at his mobile-games studio, kindly extracted the figures below. Martial has two daughters. Coincidence?
French households with three children, the first two of the same sex
If the rumour were true, among 100 such households we would expect 75 with three children of the same sex and 25 with a third child of the other sex.
Three times as many 👧👧👧 or 👦👦👦 families as 👧👧👦 or 👦👦👧 families, in other words.
Here is what the census file gave us:
| Sequence | Share, rounded |
|---|---|
| 👧👧👦 | 29% |
| 👧👧👧 | 28% |
| 👦👦👧 | 21% |
| 👦👦👦 | 22% |
| 👧👧👦 + 👦👦👧 | 50% |
| 👧👧👧 + 👦👦👦 | 50% |
The article’s conclusion: just as many 👧👧👦 or 👦👦👧 households as 👧👧👧 or 👦👦👦 households. That story about a 75% chance of the third matching the first two is AN URBAN LEGEND! In these rounded figures, we are back to fifty-fifty.
Pass on the scoop, on Facebook or Twitter. The opposite of fake news. The world has a right to know.
But where does the rumour come from?
We have a theory. Through experience or social convention, medical professionals may assume that parents all want, more or less consciously, at least one child of each sex.
Perhaps they cultivate the 75% rumour to manage expectations: “Your first two children are the same sex? Well, the third will be too, obviously. Don’t have a third to complete your collection. Do it only if you want a third child in your family!”
Prepared like this, parents risk only a harmless pleasant surprise. Everyone is protected from disappointment and its consequences. And what consequences! Ask Kee-Yoon, whose mother wanted a boy. Better still, listen to her tell the story. She left her career as a lawyer—“I’ll show Mum I’m as strong as a boy”—to become a comedian: “Mum, I’m a freeee woman!”
In her case it ended rather well, but not everyone can make a room laugh with their psychotherapy.
The explanation of how the rumour spread is the author’s hypothesis, not a documented finding about medical professionals.
MyBubelly: breaking the bank?
So, fifty-fifty every time? No ancestral tip along the lines of “For a boy, conceive at the full moon while eating cucumber”? Our grandmothers certainly had plenty of advice for steering fate towards a girl or a boy.
At publication, the French start-up MyBubelly was presenting a modern version of these natural—though controversial—methods, aimed at parents, especially mothers, with three tools:
- An app to track the menstrual cycle and ovulation.
- A diet programme in the app and supplements in a pretty box, intended to influence internal pH.
- A team of experts available to answer questions about the mother’s pH.
The original article relayed the idea that traditional methods had a fairly consistent effect on women’s pH around conception, and that a correlation between pH and a baby’s sex had been observed. It also noted that medical experts were not all convinced of the scientific—or ethical—basis of the practice.
And you thought the only pH you might ever discuss was your swimming pool’s…
Like a pool, MyBubelly came with a budget: the price quoted at publication was €149 a month for the first six months, decreasing thereafter. With a “happy parents or your money back” promise. Disappointment about the baby’s sex compensated by the joy of a refund!
Photo: Kelly Sikkema.