(1094) The accuracy of crown-rump length measurements: comparison of 5-7 with 8-10 gestational weeks

The International Society of Ultrasound in Obstetrics and Gynecology recommends for dating to use ultrasound (US) measurements at 8-13gestational weeks (GW), and to change the dating if the difference from the last menstrual period (LMP) is of 6d or more. We aimed to evaluate the accuracy of the crown-rump length (CRL) at an earlier stage of 5-7GW compared with 8-10GWand to estimate if 5d difference justifies dating correction.

Study Design: A retrospective cohort study was conducted. Data was retrieved from the medical records of women treated in the assisted reproductive technology (ART) clinic between 2016-2023 at Emek Medical Center, Afula, Israel. The LMP was calculated from embryo age and the date of transfer. The study and control groups included women who conceived by ART a singleton pregnancy and performed an US exam at 5+5-7+6 or/and 8-10+6GW, respectively. Transvaginal US was performed using the Voluson E10 BT20 device by experienced technicians at the US unit. Women with severe chronic diseases (e.g. chronic hypertension, pre-gestational diabetes, autoimmune diseases and heart or renal diseases) were excluded. The primary outcome was the accuracy of the CRL values at a range of ±4d according to Hadlock at 5+5(CRL=2mm)-7+6 compared with 8-10+6(CRL=42mm)GW. Assuming that 20% of the US CRL measurements at 5+7-7+6GW will differ at least 5d from the calculated GW compared with 10% of the measurements at 8-10+6GW, a sample size of 400 pregnancies was required (α=0.05, power=80%).

Results: Included in the study 443 women, who performed 1045 US exams (mean 2.4/woman). The study and control groups performed 575 and 470 exams, respectively, and the accuracy of CRL measurements of ±4d within the LMP was 96% and 99%, respectively (P=0.02). High rate of accuracy of 95-100% was found throughout all GWs (Table and Figure).

Conclusion: Although the control group performed slightly better, the early 5+5-7+6GW group has a high accuracy of CRL measurements and can be used for dating. We recommend dating correction if a 5d difference or more is found using transvaginal US exam during 5+5-10+6GW.