ISUOG Practice Guidelines (updated): performance of 11-14-week ultrasound scan.
International Society of Ultrasound in Obstetrics and Gynecology ., Bilardo CM., Chaoui R., Hyett JA., Kagan KO., Karim JN., Papageorghiou AT., Poon LC., Salomon LJ., Syngelaki A., Nicolaides KH.