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Maxillary gap at 11-13 weeks' gestation: marker of cleft lip and palate.
Chaoui R, Orosz G, Heling KS, Sarut-Lopez A, Nicolaides KH.
Ultrasound Obstet Gynecol 2015;46:665-9. pdf -
Prevalence of fetal facial cleft at different stages of pregnancy.
Snijders RJ, Sebire NJ, Psara N, Souka A, Nicolaides KH.
Ultrasound Obstet Gynecol 1995;6:327-9.