Hairline gender theory? Was it right for you?

It is when your child is born, and if they have a straight hairline, your next child will be the same gender. If your child has a V hairline, your next baby will be the opposite. I have two boys, my First had a straight hairline, and my second, has a V hairline, so, so far the theory was right with me.. which means, my next SHOULD be a girl... anyone else?