Naturally, one of the most common questions asked about ultrasound accuracy is: Just how accurate are the due dates that are predicted by an ultrasound?
Evidence suggests that, in the first 20 weeks of pregnancy, the first ultrasound may be the most accurate tool for predicting when your baby will be born.
But early ultrasound due dates have a margin of error of roughly 1.2 weeks, so doctors will usually keep the original due date (the one generated by the date of your last menstrual period) if the ultrasound due date is within that margin of error.
If you can't remember your last menstrual period date or if you have consistently irregular cycles, the doctor can use an early ultrasound to give you a fairly reliable due date.
It is therefore a good time in pregnancy to determine gestational age by ultrasound where the crown-rump length (CRL) is measured and compared to published reference charts.All charts generated dates significantly different to IVF dates ( all comparisons).Thus we generated a new reference chart, The Monash Chart, based on a line of best fit describing crown-rump length across 6 1 to 9 0 weeks of gestation (true gestational age) in the IVF singleton cohort.Most of these charts are based on menstrual age to estimate gestational age at the day of the ultrasound examination, based on modest sample sizes, generated many years ago using ultrasound machines of poorer resolution, or used transabdominal measurements (which gives poorer pictures relative to a transvaginal approach) [6–8].As such, there is considerable variability between current reference charts, and estimated gestational age can vary significantly depending on which chart is used.