Many women receive ultrasounds during their pregnancies. During the scan, if the baby turns so that the examiner can see between the legs, the sex can be determined. While ultrasounds are not 100% accurate, when the male genitalia is obvious - there is little reason to doubt its accuracy.
When the sex can not be determined by ultrasound and there are medical reasons for determining the sex of the unborn child, an amniocentesis can be performed. An amniocentesis inserts a needle into the uterine cavity and removes approximately 20 cc of amniotic fluid which surrounds the fetus. Exfoliated fetal cells are contained within this fluid. These cells can be cultured and the chromosomes examined and identified. Normal karotype for a female is 46,XX and normal karotype for a male is 46, XY.
If the year of conception and the age of the mother are both even numbers or both odd numbers, it will be a girl. If the year of conception and the age of the mother are one even and one odd number, it will be a boy.
If the mother picks up the key by its head, it will be a girl. If the mother picks up the key by its stem, it will be a boy.
If the mother shows you her palms, it will be a girl. If the mother shows you the back of her hands, it will be a boy.