A slightly higher ratio of boys to girls is born every year. Its tiny like 1 or 2% more boys. But this means with each baby the chance of a boy is slightly higher. Those who have girls, every time they have a baby, the chance of having a boy next is increased. Those of us with boys, the chance of having a girl decreases. Its not by a lot but for example with DS1 my chance of a girl was 49%, with this on (number 4) my chance of a girl was 47% so only a very small percentage.
With swaying its a lot to do with the environment the woman creates with in her body. She can alter her PH so that its more favourable for male or female sperm so one has a better chance of surviving and meeting the egg.
Also they say the way we eat has a basis going back to times when we would have famines and wars. Girl babies had a better chance of survival, boy babies are weaker (ironic as men always claim to be so much stronger LOL) So when times were hard, there was not a lot of food and the body would alter and be in favour of girl sperm and a lot of girls would be born, when times were better and food intake increased (along with those food types changing) it would tell the body that times are good, boys had a better chance at survival and boys would be born.
This is apparently still seen in third world countries according to the article I read on it, there is a much higher percentage of girls born in those countries.
Looking at my diet and general life style I can see that my life is one BIG boy sway.
There are also things like your own body type which can give clues (I read this on the gender dreaming site) my body type and little things about my body MAY indicate that I have a very slightly high level of testosterone in my body (though its hard to say for sure as they don't know what the average is) but little clues would suggest that.
In my maternal side girls have always been born first, girls have dominated (going back to my great grand mother, and my great great grandmother they both had 1 brother each and 6 or 7 sisters) My Nan was the eldest of 2, she had a brother, their Dad was then killed in the war and their Mum never remarried. My Nan had 1 daughter and I was the first born grandchild. My Mum then had twin boys, my Dad remarried and had another boy. My Dad was adopted so we can't know his family pattern. But as you see he has 1 girl and 3 boys.
The thing is we can't know 100% if swaying does work, yes some people sway and they get the gender they wanted, but it could be a coincidence because there are those that sway and don't get what they wanted.
They say its scientifically based that men produce equal numbers of sperm, and also that the way it is produced means that you can't have one gender be faulty and the other healthy to explain it. I don't know though. I know a lady on the due in october thread on gender dreaming is on her 7th boy! And there are a LOT of us on our 4th.
I did plan on swaying next time, but number 5 is looking less likely now, and I think it wouldn't help any desire I felt, it would just get my hopes up even more. This baby took long enough to make and I'm now just grateful his on his way at all. I think at the end of it all you will get what you are given and what you are meant to have whatever you do. I read so many stories of those who said "no more babies" after their sway failed or failed twice and then had a surprise pregnancy and got a girl while doing everything 'wrong' (in swaying terms)