thumb|left|Sign in an Indian hospital stating that prenatal sex determination is not done there and is illegal thumb|Ultrasonography image showing the fetus is a boy The earliest post-implantation test, cell free fetal DNA testing, involves taking a blood sample from the mother and isolating the small amount of fetal DNA that can be found within it. When performed after week seven of pregnancy, this method is about 98% accurate.
thumb|left|Sign in an Indian hospital stating that prenatal sex determination is not done there and is illegal thumb|Ultrasonography image showing the fetus is a boy The earliest post-implantation test cell free fetal DNA testing involves taking a blood sample from the mother and isolating the small amount of fetal DNA that can be found within it When performed after week seven of pregnancy this method is about 98% accurate