[Advances in the mass screening of Down's syndrome in early and middle stages of pregnancy].
Hang
A
A
Chen
X
X
D004314:Down Syndrome / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis; D014463:Ultrasonography