Gender Statistics

63752146 - stippled vector map of global population densityHaving experienced the luxury of having three boys, I (and I’m sure I’m not alone) often find myself thinking how often this happens and why.  During one of my many night feeds, I took to the internet to see the stats and I wanted to share them, as my findings really are fascinating.  

There are many hypotheses about why there are slightly more boys born each year in the world (51% boys/49% girls), but no one knows for sure why. Here are a couple of the main theories:

  • Males are more fragile, therefore it’s nature’s way of evening out the balance (lol).
  • Male sperm may have a speed advantage over female sperm, more often winning the race to fertilise the egg and resulting in more male conceptions.

Regardless of the reason, the ratio remains constant year to year throughout history. 

Are Boys or Girls Preferred?
I realise this is a stupid question!  Once a parent is handed their baby there’s an undeniable love regardless of its gender.  I guess what I was more interested in was what size is a ‘normal’ sized family nowadays and my findings suggested they may be something to do with gender why people stop.  Many people stop because they have got to a certain number and others stop when they have the desired genders.

  • Parents are slightly more likely to stop having children if the first child is a girl.  If the first child was a boy, 70% of people went on to have a second child. Whilst, when the first child was a girl, 68% of parents went on to have a second child. 
  • If parents had a boy and a girl, the results came out at 39% of parents went on to have a third child.  Of the parents who had two same-gender children, two boys previously, meant 46% of people went on to have a third child and two girls previously, meant 43% of people went on to have a third child.  These results combined are (same gender) 45% of parents went on to have a third child.
  • It was suggested that a family of two boys and one girl families are the most likely to have a fourth child.  Three boys meant 29% of parents went on to have a fourth child. Two boys and one girl was 35%.  One boy and two girl families was the lowest at 20%.  Finally, three girls resulted with 26% of families went on to have a fourth child.  These results combined showed a same gender family (all boys or all girls) would go on to have a fourth 28%,  whilst mixed gender (two boys, one girl or two girls, one boy) was 26%.  

Odds of Having a Girl or Boy 
Following the same survey it was found, the odds of having a girl seem to decrease after having each boy, but only very slightly. 

0 previous children = 49% chance of a girl next
One boy previously = 50% chance of a girl next
Two boys previously = 47.7% chance of a girl next
Three boys previously = 43.6% chance of a girl next

The odds of having a boy seem to increase after having girls, except after two girls, when a third girl is more likely.

0 previous children = 51% chance of a boy next
One girl previously = 54.5% chance of a boy next
Two girls previously = 46% chance of a boy next 
Three girls previously = 52.7% chance of a boy next

Given the charts above, it looks like you are only very slightly more likely to have a boy, regardless of previous children. This is probably due to the overall 51%/49% boy/girl birth ratio.  But those percentages are so close!   

Odds of Having an All Same Gender Family
If there are roughly even odds of having a boy or a girl with each baby, given the laws of chance we should still expect to see some all same-gender families, even in large families. Here is the number expected to be seen:

First child – boy/girl = 51%/49%
Second child – same sex/ different sexes = 50%/50%
Third child – same sex/ different sexes = 25%/75%
Four child – same sex/ different sexes = 12.5%/87.5%
Fifth child – same sex/ different sexes = 6%/94%
Sixth child – same sex/ different sexes = 3%/97%
Seventh child – same sex/ different sexes = 1.6%/98.4%

There’s a bit of food for thought for you all… 

Much love
Rebecca D5463E0A-2E16-4AB6-AC32-856DCD5331D6

One comment

  1. Hi Rebecca
    I am interested in your journey as a parent.
    One thing I have noticed with the research facts that you have shared is that you make no mention of Chromosomes. A male is typically X and Y chromosomes while a female can only be XX . It is the male that determines the sex if the child (generally speaking) but the “Race” with the sperm to the egg does play a huge part in it.
    I love the fact that you mention the instant bond, regardless of your wishes. This is something that I have found to be the most increadible feeling anyone can ever experience.
    Love to you all xxx
    Angela Davies

    Liked by 1 person

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