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Probabilitiy of gender for third child...

69 replies

minicommandant · 15/11/2006 22:12

Didn't really know where to put this, but hope someone can shed some light. A friend's midwife is telling her that because she already has 2 boys, there is a 75% chance that her 3rd baby will also be a boy. As I also have 2 boys and am planning a 3rd, I would be really interested to know if there is a proven statistical basis to this! It wouldn't affect the decision, just interested to know the odds!

OP posts:
nutcracker · 15/11/2006 22:13

Haven't a clue, but I had 2 girls and then a boy.

cece · 15/11/2006 22:14

Surely it is 50/50 as the probability returns to that for every baby. Surely the number of babies you have doesn't effect the probability for each individual one.

collision · 15/11/2006 22:15

I think the odds are higher of having another boy if you have 2 boys already.

threebob · 15/11/2006 22:15

I heard this too from a friend's midwife. Something to do with cervical mucus being hostile to likely female candidates. My thought was that only 2 boy babies - it could just be a coincidence.

JanH · 15/11/2006 22:15

I had 2 girls and then a boy too.

There was another thread a bit like this recently - strictly speaking it's a 50:50 chance every time, but somebody quoted some condition or other that means it actually isn't (helpful, eh?)

Will see if I can find it for you, mc

edam · 15/11/2006 22:16

Logically you'd assume Cece is right, but I'm sure I've come across a statistic that shows the third child is more likely to follow the pattern in a single-sex family. Can't remember how it works but presumably some men just produce more xs or ys.

NotQuiteCockney · 15/11/2006 22:17

It's definately not 50/50. Some couples are more likely to have one gender, it's down to cervical mucous, which reflects a lot of different things.

(I really was coming on here to say that yes, there is a 100% chance your child will have a gender.)

LadyOfTheFlowersIs1Baby1Bump · 15/11/2006 22:17

ooh ooh, ive been meaning to ask views on this. i have 2 boys and would love a girl aswell....
dh has a brother and i have 2.

Olihan · 15/11/2006 22:18

I think edam's right, some men just produce more x or y sperm, therefore if you've got 2 the same then the third is slightly more likely to be the same.

NotQuiteCockney · 15/11/2006 22:20

Hmm, I think each man has to have 50/50 X and Y sperm, as each sperm is made by splitting a normal cell, and each normal cell has one X and one Y. Oh, I guess if your bloke is XYY, but I think that's pretty rare, isn't it?

dinosaur · 15/11/2006 22:21

This reply has been withdrawn

This has been withdrawn by MNHQ at the poster's request.

cece · 15/11/2006 22:22

so what if you have one of each already?

NotQuiteCockney · 15/11/2006 22:24

Some people do have 50/50 odds, or near enough.

There are a lot of factors that go into gender selection. Cervical mucous and time (within cycle) of intercourse are two big ones. Obviously time within cycle can vary from conception to conception, and there are plenty of things that change your cervical mucous.

There are actually some interesting sociobiological explanations for gender probailities that I can't get into tonight, but can go on about for hours some other time ...

minicommandant · 15/11/2006 22:25

Thank you all! Especially NotQuiteCockney whose post gave me a good laugh before I sign off for the night. Look forward to seeing if we get any "proper" answers (no offence intended!) from those in the biz overnight and whose theory is right...

OP posts:
cece · 15/11/2006 22:26

Glad to know my mucous is hospitable to all

edam · 15/11/2006 22:26

I'm sure NQC's right and it's more to do with mucus - I was only speculating given that I had a vague memory it wasn't 50/50.

minicommandant · 15/11/2006 22:27

oh, I meant NotQuiteCockneys earlier post re having A gender. This latest one crossed with mine. Hope you do get chance to bang on about stuff later as sounds like plenty of us are interested.

OP posts:
Olihan · 15/11/2006 22:40

Aren't there more boys born that girls on average anyway? 51 boys to 49 girls sort of thing? I'm sure I've read that somewhere - probably the same place as the x/y sperm thing so maybe not the most reliable source!!

twickersmum · 15/11/2006 22:44

you should get this book...
3 friends "tried" for a specific gender and all got it!

coppertop · 15/11/2006 22:47

I had 2 boys and then a girl. 8 months on I still can't quite get used to having a girl.

NotQuiteCockney · 16/11/2006 10:29

Yes, there are generally slightly more boys born than girls. This is probably explained by the fact that male sperm swims faster than female sperm. Female sperm travels slower, but is more hardy, so you're more likely to have a girl if you have intercourse a while before ovulation, and the sperm has to hang about, iyswim.

Ok, the sociobiological explanation is a bit complicated, and mostly based on what I've read in Hrdy. Basically, there's evidence that other primates do sex selection for their own advantage. For example, in a primate species which is matrilinial/matrilocal (girls stay in the troop they're born to, and if your mum is important in the troop, you probably will be too), the top women mostly have girls, to carry on their empire. The bottom women have boys, who will generally move to another troop, and have a fresh start, anyway.

For primate species that are patrilinial/patrilocal, top women have boys, bottom women have girls.

So primates definately have the capacity for status-based sex selection.

Humans are generally patrilinial. Also, historically, if you were well-off and in good health, and likely to produce a really smart strong and healthy child, you'd be better off having a boy. Because historically, women generally all had about the same number of kids (somewhere between 0 and 10, I'd say), but the bulk of men would have 0, and a small number would have hundreds or even thousands (think emperors with harems etc etc. Or Wilt Chamberlain, in the modern day). So if your body thinks you're in a great position, likely to have a great kid, a boy is a good idea. Otherwise, better to play it safe, and have a girl.

I have this theory partly because I live in a socially mixed area - lots of working class people, lots of middle class people. Almost all the local mums I know are middle-class, and almost all the local mums I know have boys. But then, most of us feel quite rich and priviledged, because, compared to our neighbours, we are.

So there, you asked for a real blurb on it, you got it.

I suspect that intercourse timing and dietary changes which hopefully will affect the mucous are more likely to bring you the desired gender of baby than convincing yourself you're poor.

NotQuiteCockney · 16/11/2006 12:07

(I did warn you that I could go on for hours ...)

pinktinselanddollymixtures · 16/11/2006 13:02


Just thought i'd add to the thread.

I am one of three girls. I have just had my third daughter (no boys). My older sister is due her 3rd girl in January (also no boys).
My younger sister has only got the one child and guess what?'s a girl.

Does there seem to be a pattern here...?

lulumama · 16/11/2006 13:04

how interesting NQC...are you a biologist or something of that ilk?

FWIW it is predominantly girls within my immediate family,..although i have one of each and am not planning anymore...but girls outnumber the boys...

throckenholt · 16/11/2006 13:15

not yet waded through the whole thread. BUT - going back through family history it is clear that in most large families here is a roughly equal number of boys and girls - even if they come in a series of one sex or the other.

So generally for the population as a whole it is roughly 50:50. For an individual it may be skewed by physical conditions (ed cervical mucus), or eg I think diabetic men produce more female than male sperm.

At the end of the day - you have no say in the matter anyway - you get what you get.

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