Some of the findings support old wives tales that any mom or midwife will tell you. For example, male fetuses are generally more active than female fetuses. How often have you heard a mother-to-be react to a hearty kick with the comment, "I know this one is a boy."
The male fetus produces testosterone and the female fetus produces estrogen. So the hormonal system is already setting up boys to be more assertive, even before they're born. In addition, the female fetus produces more serotonin, than the male. Serotonin, is a hormone that calms you down, and many people take serotonin substitutes to aid sleep, especially women after menopause.