Natural Methods for Choosing the Sex of Your Child
The Shettles method is arguably the most well-known natural strategy for choosing the sex of your child. Developed three decades ago by Landrum B. Shettles, MD, PhD, the plan involves timing intercourse to a woman's cycle and assuming certain sexual positions.
In his book How to Choose the Sex of Your Baby, Shettles explains that the male (Y) sperm is smaller, faster, and more short-lived than the female (X) sperm. Because of this, it is better for boy-desiring couples to have sex closest to the time when a woman's egg is released (ovulation). This way, the speedy male sperm could get to the egg sooner than the female one.
The Y chromosome apparently also enjoys an advantage over its counterpart when the sperm is discharged as close as possible to the opening of the cervix. This is achieved through rear entry intercourse (man enters woman from behind).