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2. Maternal serum alpha‐fetoprotein measurement: a screening test for Down syndrome;Cuckle HS;Lancet,1984
3. Placental histology in fetuses between 18 and 23 weeks' gestation with abnormal karyotype;Kuhlmann RS;Am J Obstet Gynecol,1990
4. Collaborative AFP Study. Maternal serum alpha fetoprotein measurement in antenatal screening for anencephaly and spina bifida in early pregnancy;Wald NJ;Lancet,1977