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Performance of screening for aneuploidies by cell-free DNA analysis of maternal blood in twin pregnancies.
Bevilacqua E, Gil MM, Nicolaides KH, Ordonez E, Cirigliano V, Dierickx H, Willems PJ, Jani JC.
Ultrasound Obstet Gynecol 2015;45:61-6. pdf -
Cervical length at 23 weeks in twins in predicting spontaneous preterm delivery.
Souka AP, Heath V, Flint S, Sevastopoulou I, Nicolaides KH.
Obstet Gynecol 1999;94:450-4.