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

A: 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.

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

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 23^rd 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 23^rd 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.

If you already have a boy, the chance that the next baby is also a boy is 50 percent

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.