Ultrasound dating at 12-14 or 15-20 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
Objectives To determine the accuracy of established ultrasound dating formulae when used at 12-14 and 15-20 gestational weeks. Methods A total of 363 singleton pregnancies conceived after in-vitro fertilization (IVF) and randomized to a dating scan at 12-14 or 15-20 gestational weeks were studied. 'True' gestational age was calculated on the basis of the day of oocyte retrieval and was compared to