Not protruding belly button does not necessarily give birth to a girl, and the protruding or not protruding belly button has nothing to do with the sex of the fetus. The belly button does not protrude and pregnant women’s abdominal wall skin elasticity and fetal size, if the skin elasticity is good, sufficient tension, the fetus is small, the abdominal wall is not easy to be squeezed by the fetus, it is not easy to appear belly button protrudes, and can not be based on the belly button does not protrude to infer or suspect that it is a girl. The idea that a girl is born if her belly button does not protrude is not valid and has no scientific basis. The sex of the fetus depends mainly on the male chromosome, if the Y chromosome sperm and egg combination is male, when the X chromosome sperm and egg combination is female, the belly button can not reflect the male and female. During pregnancy, pregnant women should not judge the sex of the child according to any folklore, so as not to affect their mood.