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Prefrontal space ratio: comparison between trisomy 21 and euploid fetuses in the second trimester.
Sonek J, Molina F, Hiett AK, Glover M, McKenna D, Nicolaides KH.
Ultrasound Obstet Gynecol 2012;40:293-6. -
Ear length in trisomy 21 fetuses at 11-14 weeks of gestation.
Sacchini C, El-Sheikhah A, Cicero S, Rembouskos G, Nicolaides KH.
Ultrasound Obstet Gynecol 2003;22:460-3.