According to a study done by researchers at Maastricht University in the Netherlands, the longer it takes a woman to get pregnant, the greater her chances of having a boy.
See, one reason why some women have trouble conceiving is that the mucous around their cervix is extra thick. That makes it harder for sperm to reach the egg. Now, the Y chromosome, which is the one that makes boys, contains less DNA than the X chromosome, which makes girls. This means that sperm that contain a Y chromosome are a bit lighter than sperm with two X chromosomes.
The lighter, Y chromosome carrying sperm are faster and better at swimming through thick cervical mucous. At least the Y chromosome carrying sperm may have a better shot at getting through the mucous and reaching the egg. So, according to the study, it may be the case that women who take a long time to get pregnant because of thick mucous have a better chance of having a boy.