Dating ultrasound measurements
OBJECTIVES There are no international standards for relating fetal crown-rump length (CRL) to gestational age (GA), and most existing charts have considerable methodological limitations.
The INTERGROWTH-21(st) Project aimed to produce the first international standards for early fetal size and ultrasound dating of pregnancy based on CRL measurement.
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.
In the first trimester, there is a very little biologic variation in fetal size compared with later trimesters.
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.
METHODS Urban areas in eight geographically diverse countries that met strict eligibility criteria were selected for the prospective, population…
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Pregnancies that resulted from frozen embryos transfer, complicated by fetal structural anomalies, delivered before 24 weeks, or had missing data were all excluded.It should be possible to generate very accurate reference charts by using a large in vitro fertilisation (IVF) cohort where CRL measurements could be correlated with gestational age precisely calculated from date of fertilisation.Accuracy could be further enhanced by using measurements obtained from high-resolution transvaginal scans by sonologists specialising in Women’s Health.We examined CRL lengths at 6–9 weeks of gestation measured in a large IVF cohort where gestational age could be calculated from date of fertilisation.We assessed the ability of six commonly used reference charts to accurately date these pregnancies.