The side you sleep on while pregnant has absolutely no bearing on whether you're having a boy or a girl. This is simply an old wives' tale.
Many myths surround pregnancy, including predicting a baby's sex based on symptoms, cravings, or even sleeping positions. However, these are unfounded. Scientific evidence does not support any connection between the side you sleep on during pregnancy and the sex of your baby.
While sleeping on your left side during pregnancy is often recommended by healthcare professionals due to potential benefits for blood flow and organ function, this recommendation is independent of the baby's sex. Sleeping on your left side can help take pressure off the vena cava, a major blood vessel.
Ultimately, you should sleep in whatever position is most comfortable for you during pregnancy, while keeping in mind any specific recommendations from your doctor. The baby's sex is determined at conception by the sperm that fertilizes the egg.
