RT Journal Article SR Electronic T1 Prenatal Diagnosis and Prognosis JF Journal of Medical Genetics JO J Med Genet FD BMJ Publishing Group Ltd SP 504 OP 504 DO 10.1136/jmg.28.7.504 VO 28 IS 7 A1 Helen Kingston YR 1991 UL http://jmg.bmj.com/content/28/7/504.abstract AB