Ultrasound dating at 12–14 or 15–29 weeks of gestation? A prospective cross-validation of established dating formulae in a population of in-vitro fertilized pregnancies randomized to early or late dating scan - Saltvedt,S.; Almstrom,H.; Kublickas,M.; Reilly,M.; Valentin,L.; Grunewald,C. (Ultrasound Obstet Gynecol, 2004)