Some people believe the Ramzi theory can determine fetal sex as early as 6 weeks into pregnancy. All this boils down to just one question, how often do married couples have sex, usually? How couples have sex to USA Today How couples have sex, 20 to 30 percent of men have little or no sex drive, and 30 to 50 percent of women say they have little or no sex drive. What makes a carb good and what makes it bad? Is It for Real?