The basic foundation of the Shettles methodology is that men produce two types of sperm, the X (female) and Y (male). The Y (male) sperm are smaller and weaker, but faster than the X (male) sperm. To tip the balance in your favor of having a child of your preferred sex, the Shettles method has several recommendations to manipulate which sperm (X or Y) will most likely reach and fertilize the egg first.

You’ll want to start tracking your monthly cycle using an ovulation predictor kit available at most pharmacies. The Shettles method contends that if you have sex close to the ovulation date, the chances of conceiving a boy are more likely. The Y sperm will make it to the egg quickly and you’ll have a boy. If you have sex two or three days before ovulation, the Y sperm will die off and there will be more X sperm waiting for the egg to appear, greatly increasing the chances of conceiving a girl.

Another important factor is the pH of the vagina. The pH balance of your vagina changes to alkaline on the day you ovulate and making a favorable environment for Y sperm, enhancing the prospects of conceiving a boy. An acidic environment will kill the Y sperm first, leaving a greater number of X sperm left to fertilize the egg, resulting in a baby girl.

The pH balance of the vagina also comes into play when determining which sexual position to use. Deeper penetration positions favor conceiving a boy, because it places the sperm closer to the egg and gives the faster male sperm a head start. A woman’s vagina is more acidic towards the front, and Dr. Shettles recommends the missionary position for girls where the male sperm will either slow down or die in the more acidic environment.

Following the recommendations of the Shettles method can help you swing the balance in conceiving a boy or girl in a safe and natural way.