Ultrasound dating at 12–14 or 15–20 weeks of gestation? A prospective cross‐validation of established dating formulae in a population of <i>in‐vitro</i> fertilized pregnancies randomized to early or late dating scan

Abstract

Ultrasound dating formulae originally intended for use in the middle of the second trimester do not necessarily perform well when used for dating earlier in gestation. The systematic and random error of any dating formula must be assessed for the gestational age interval in which the formula is intended to be used.