According to statistics, one newborn is born every 4 seconds in China. Corresponding to this number, Chinese pregnant women are a very large group. Many years ago, in order to prevent birth defects of newborns, expectant mothers chose the method of amniocentesis for prenatal examination, but this method has a low accuracy rate and a 10% risk of miscarriage, which makes many families discouraged. Painless obstetric examination based on genetic testing technology has been sought after by more and more people.