theories on natural sex selection?

[cathyspam]

i have a non MN friend () who is currently TTC and she is fairly biased towards having a girl as she already had 3DS's and I have offered her all the info I know about this which is not a lot but just wondering if anyone knows more about it?

There's a book on it somewhere, I will track it down and post a link to it, but it has something to do with diet etc, also, have heard that having sex 3 or more days before ovulation and then not again is more likely to result in a girl as female sperm live for longer but are slower swimmers but male sperm are faster swimmers but don't live as long. Not sure whether any of this really works though - I'm sure there are some who will say it did and some who will say it didn't, in reality, I guess it's impossible to know if it had to do with lifestyle/diet etc or whether it was just pure luck.

My understanding is that male sperm is lighter and swims faster, female sperm is heavier and swims slower. So the theory goes, if you know when you are ovulating and have sex on that day then there is more chance of conceiving a boy. If you have sex a few days before you ovulate then the male sperm may have died by the time you ovulate and the female sperm will be just be getting there.

There is also the theory that male and female sperm thrive in different environments - one in alkali and one in acid - unfortunately I can't remember which way around.

I read a book when trying to conceive, the book was by Dr Sarah Brewer and was primarily for conception over 35 but is applicable for any age etc.

I have a dd (which is what I wanted - so the theory worked - or I was lucky) dd2 is currently 3 days late! HTH