We have 3 children, they are all boys, and we now want another child. Should we give up our hope for a girl?

Even after 3 children of the same sex, your chances in the next pregnancy having the same one is about even.

Even after 3 children of the same sex, your chances in the next pregnancy having the same one is about even.

Having already 3 boys you may think it’s a foregone conclusion  that the next baby is going to be another boy, but in reality your chances are about equal between a boy and a girl.
It’s not that unusual to have 3 children of the same gender in a row. This actually happens in one out of four couples who have 3 children.

This is how the baby’s gender is determined:

  • Each of the man’s sperms and each egg carry 23 chromosomes. The sperm and the egg combine at fertilization for a total of 46 chromosomes which come in 23 pairs.
  • The 23rd chromosome is called the “sex-chromosome”. In sperms it is either an  X- or a Y-chromosome, while in the woman’s egg it is always X.
  • If an X-bearing sperm fertilizes the egg, the resulting 23rd pair is XX, a girl, and if a Y-bearing sperm fertilizes the egg, the result is XY, a boy.
  • It is therefore the sperm that decides the baby’s gender:  X-bearing sperms result in girls, and Y-bearing sperms in boys.
  • In general, X- and Y-bearing sperms are about equally distributed in the ejaculate, so each time there is about an equal 50-50 chance for each gender.

Let’s say, a couple has a boy. The chance that the next baby is also a boy is 50%.

It’s all a matter of mathematics. A couple having 4 children of the same gender in a row happens actually more often than you might think. In fact one in eight couples (12.5%) with 4 children have 4 of the same sex.

Here's how it goes:

  • Couples with 2 children: 50% of couples have 2 girls or 2 boys, and 50% of couples have 1 girl/1 boy
  • Couples with 3 children: 25% of couples have 3 girls or 3 boys, and 75% have 1 boy/2 girls or 1 girl/2 boys
  • Couples with 4 children: 12.5% of couples have 4 girls or 4 boys,  37.5% will have 1/3 and 50% will have 2/2.
  • Couples with 5 children: 6.25% have 5 the same sex and in couples with 6 children, 3.125% will have the same sex.

 

All same sex

Different sexes

 

2 children

50% G/B

50% B/G 

 

3 children

25% all girl or all boys

75% BB/G or GG/B

 

4 children

12.5% all girls or all boys

37.5% 1B/3G or 1G/3B

50% BB/GG

5 children

6.25% all boys or all girls

25% BBBB/G or GGGG/B

68.75% GGG/BB or BBB/GG

6 children

3.125% all boys or all girls

12.5% BBBBB/G or GGGGG/B

46.875%: GGGG/BB or BBBB/GG

 

 

 

 

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