Do you know why this is?

[YoungScrappyHungry]

Just thinking out loud really and can't really find anything on Professor Google.

Why do some families have multiples of the same sexes? I know families with 5 girls and another with 4 boys. Is it pure chance? As surely with each pregnancy it goes back to 50/50 each time? Or is there some scientific reason why some seem more predetermined than others?

I'm 7+2, DH has 3 boys and I'm therefore convinced this will be the same. Is that logical??

I believe it’s the sperm that determines sex so it’s just dependant on which gets there first. Also some women seem unable to carry certain sex. I know several women that have miscarried certain sex several times but have had successfull pregnancies with the other.

I recently heard that it's not always 50/50 in sperm and some men have more of one or the other genetically which I found interesting!

Assuming the chances are 50/50 for each birth, the chances of:
1 baby of the same gender is 1/1
2 babies of the same gender is 1/2
3 babies of the same gender is 1/4
4 babies of the same gender is 1/8

1/4 or 1/8 aren’t so small odds!

Also, I think a significant proportion of three-children families choose to do so in the hope for elusive other gender when they already had two of the same (based on the sample size of one family with three boys that I know... though my grandmother had three boys but then went on to have two more daughters). If this were the case for ALL third and then fourth babies, then the likelihood of all the same gender would be 1/2 of all three and four children families within a population. As this isn’t the case I’d expect the real numbers to be somewhere between 1/2 and 1/4, and 1/2 and 1/8 respectively.

These are two stats I've heard:

1. If you've already had 2 or the same sex then your third will be the same too.
2. If your DH is one of all boys and their dad was one of all boys then you're more likely to have boys.

More likely I should have said