If you had two girls, would you expect a third baby to be another girl?

[AngelsInWinter]

I would. DP and I are ttcing and I wholly expect it to be another girl if we are successful (this doesn't bother me in the slightest; I love my girls so why wouldn't I want another!). We wouldn't find out the sex at the scan anyway.

(Fwiw I also have a boy, but he has a different father).

meditrina
I think the chances of that are a leeeeetle smaller than 50%.

I had 4 boys - of my 8 pregnancies one was a female, one unknown and the other 2 would have been boys too.
I worked with somebody who had 7 sons (no girls)
I worked with somebody else who had b/g/b/g/b/g.
I know somebody with 4 girls.

The multiple of anecdote does not data make

'Tis 50:50 or thereabouts - live birth rates are slightly skewed in favour of males due to higher infant mortality in males (some clever trick of Mother Nature that I will not pretend to understand).

I was quite keen that DC1 would be a boy because I (eldest) always wanted to have a big brother. Once DS1 was in place I had no preference.
Everybody assumes I had 4 'trying for a girl' but it was not so.

Every now and then DH says "wouldn't it be nice to have a girl?" to which I reply "what you do with your second wife is up to you". I am so done with looking after infants, so so finished .
Anyway, I am hoping that menopause will solve this possibility for me very soon...

Good grief, I went on a bit - sorry

Pacific - me and DP pissed ourselves at your "second wife" comment so your essay was well received! I always say stuff like that...

Also never thought of the "limited supply" thing; that is so true. Although I have a boy (not DP's) so I don't have a problem carrying boys, if that exists.

Yup. It's about 1:18000 in UK. Given birth rate, that's roughly 450 babies per year.

Wow, that's more than I thought.

eyelet, neonatologist said the same to us when we were waiting for our dr to be born prematurely. If she was a girl, she'd have a better chance of survival. Unfortunately for her and us, it was not to be.

Hope your dd is ok

We are considering a 3rd after 2 girls and fully expect another. Happy either way.
I am one of 5, 4 girls before boy came along. DH is one if 6, 4 girls and 2 boys.
Girls do seem to be genetically favoured.

Birth rate is more like 51:49 Boys:Girls.

The formatting's going to get messed up if I do it, but if you draw out my table again and add an extra split on each of those outcomes you'll see you end up with 8 outcomes.

BBB
BBG
BGB
BGG
GBB
GBG
GGB
GGG

If we use 50/50 rather than 51/49 for simplicity, each of these has a 1 in 8 chance of occurring, or 12.5%.

That makes the chance of having 2 girls, 1 boy, 3 in 8 or 37.5% - just over half.

The chance of having 2 of one sex and one of the other, overall, is double that - 6/8 or 75%. Whereas the chance of having 3 girls overall is 12.5% or the chance of having all 3 the same sex is 25%.

When you look at it that way, it would seem like you have a higher chance of conceiving a boy when you've had two girls, but this isn't the case.

If you had one daughter and wanted to know the possibility of the sexes of your future two children, you have to rule out the first four possibilities in my list, because you've already had the first one and she isn't a boy. Hence, you have four outcomes, GBB, GBG, GGB, GGG, each with 25% probability. Your chance of having 2 girls, 1 boy goes up to 50% rather than 37.5% but the chances of all the same sex vs 2:1 are the same - 25% and 75% respectively.

In your situation you already have two girls, which narrows this further. GBB and GBG are ruled out. The only two possibilities are GGB or GGG. They are equal so you have a 50% chance of either one happening. Therefore, you are more likely (twice as likely) to end up with a family of three same-sex children at this point than a family who currently have one child, or no children. But that's just because part of the puzzle is already completed.

(Sorry I am leaving your DS out totally, but you didn't mention him until later and you were interested in the probability aspect :))

Boring maths part alert
For people interested in calculating probability like this: If you want to calculate the probability using 51:49 you just need to multiply for each level, so 51% x 51% x 49% for BBG for example. If you already know the outcomes of the earlier branches, then you need to change the probability of those branches to 100% for the real outcome and 0% for the false outcome.

For example, family with one daughter. The chance of having a girl first is 100% (it has happened). The chance of having a boy first becomes 0% (it didn't happen). The chance of the later branches where the outcome is still unknown remains at 51%/49%. Follow along the branch and multiply all figures together. You'll see that anything beginning with B comes out at 0% whereas GBG, GGB, GBB, GGG all come out at 25% each.

We had a 'accidently' 3rd baby, after 2 daughters. He is the first boy in both sides of the family for 35 plus years.

But to be honest we didn't care what he was as long as the baby was healthy.

My 3rd DD was and I would probably expect dc4 to be if I had any more. He is the only GS out of 10 grandkids as well.

Sorry 3dds DF is the only DGS out of 10 GKs

Bertie, wow, epic post

You are right wrt the maths.
But whether this baby is going to be a girl or boy the probability is always 50%: even after 10 boys the next one is just as likely to be a girl.
50% or thereabouts.

And there may be a problem carrying boys as I have had 3 MC in between 3 dds but didn't go for tests as I am not having anymore kids

Correct Pacific :) That happens when you follow the chart - the last option is always 50/50 so if you know the outcome up to that part then it's always 50/50.

I suppose after 10 boys, though, one could assume that there was a problem genetically in either mother or father causing XX embryos not to form or to miscarry for some reason. But yes when you assume no genetic issues in mother or father, the probability is always 51:49 for every baby conceived in the world at any time. (Do we need to get into IVF etc? Selective screening? )

The 50% thing doesn't account for the fact that someone with two females might be more favourable to having girl babies? Y chromosome attaching better or whatever? Is this true?

No, do lets not go there!

I suppose it depends whether we are asking 'chances of one or the other chromosome fertilising an egg' or 'live birth' or 'alive at 5 years of age' .

Some genetic conditions are bound to either the Y or X chromosome and as affected pregnancies often end in pregnancy loss, that can skew the odds.
Also, interestingly, individual semen cells that carry a genetic problem are often slower than the other 'swimmers' so are less likely to actually achieve fertilisation.

Now I've confused myself…. FFS.

I'm going to stick to 50:50 or so close to it it doesn't matter

No, it doesn't. The 50% thing is assuming there are no problems.

You'd have to look up the likelihood of such problems to be able to incorporate those figures in. Certainly there are genetic issues, either which make the sperm of one sex weaker so it doesn't survive long enough or (more likely) that there is a faulty gene which only appears in the X or the Y, and hence a pregnancy of one sex would miscarry, while the other sex would be fine.

The chance of having 2 girls is 25% overall anyway (or 24% girls, 27% boys if you want to use 49:51 as a baseline) so it would be very common and not a particular reason to suspect problems carrying the opposite gender.

Right but assuming no genetic problems, alive at 5 years of age is irrelevant. We're talking about gender and birth order. Still birth and early childhood death may affect (boys?) slightly higher than girls but IIRC that balances roughly out with the 51:49 thing anyway.

So I suppose I'm talking about live births.

I have two DSs and a younger DD. I always assumed it was pretty much 50:50.

Bertie, I suppose it also depends if one is looking at statistics or individuals.

Anybody who finds themselves pregnant after having had a previous child/children has the same chances for whatever sex as they did before.

Having had x number of B or G before, does not influence what you are likely to have next (sex chromosome-bound genetic disorders excluded).

Good grief, I am glad I will never have to worry about this again!

My third is a boy after two girls. DH has two older children a girl and a boy. His 4 siblings have girls. The odds were on Ds being another girl.
, but he wasn't.

Thanks for the statistics, guys! We can have fun guessing either way.

If I remember rightly I did actually think the third baby could be a boy or a girl until the sonographer said "I haven't seen anything that makes me think it's a boy... But the legs are very close together, so DON'T buy anything pink!" It was her that put doubt in my mind. I'd forgotten about that.

Ooh and I did mention DS in my OP, honestly! :)

Interesting thread!

I'd heard the 75% statistic too, never felt right to me, glad to see it all explained and it does stay 50/50.

These are the ones I was talking about. Boys more likely until you have two girls. So we have done the less likely thing every time with girl girl boy (still in utero!). These are USA stats but probably not that dissimilar here?

www.in-gender.com/xyu/odds/gender_odds.aspx