Dating ultrasound measurements updating from sp2 to sp3
Of our cohort of 1268 pregnancies, 84 were scanned twice, and 2 pregnancies were scanned three times, giving a total population size of 1182.
In these pregnancies with multiple scans, all data were included in the analysis as discrete values.
As such, there is considerable variability between current reference charts, and estimated gestational age can vary significantly depending on which chart is used.We restricted our analysis to those who had fresh embryo transfer since we were concerned with the need to add the time from egg pickup to freezing, together with the time from subsequent thawing to transfer might introduce inaccuracies.We determined gestational age on the day of the ultrasound (IVF dates) by nominating the day of egg pickup and fertilisation as day 14 of gestation. Note that some charts did not have corresponding gestational ages for all measurements which accounts for the variability in sample size seen in the comparison of charts.Given all these charts showed inaccuracies in their ability to date these IVF pregnancies, we developed a new reference chart based on IVF dates in a singleton cohort.We retrospectively obtained clinical details on 1268 singleton IVF pregnancies conceived using a fresh embryo transfer cycle, had a transvaginal first trimester ultrasound done between 6 ( 1d) to 9 ( 0d) weeks of gestation where CRL were measured, and progressed to viability (24 weeks of gestation).