EP08.03: First trimester fetal size in pregnancies conceived by assisted reproductive technology compared to reference curves

To compare the Crown–rump-length (CRL) in pregnancies conceived by assisted reproductive technology (ART) with standard reference growth curves for CRL. This study took place at St. Olav's Hospital, Trondheim University hospital, Norway, from February 2022 to January 2024, as part of a larger project examining fetal growth after ART called GrowART. 118 women with a live and normally sited pregnancy after single blastocyst transfer were included and scheduled for examination 42 and 70 days after embryo transfer, corresponding to gestational week (GW) 8+5 and 12+5. Three patients miscarried and one withdrew from the study between the two examinations. One missed the appointment, leaving 113 pregnancies for final analyses. We compared our findings with two international standard reference curves for fetal growth: Robinson's growth curve and INTERGROWTH-21. Mean CRL was 20.8mm (95% CI [20.6-21.0], range 17.9-24.7mm) in GW 8+5 and 67.7mm (95% CI [67.0-68.3], range 57-75mm) in GW 12+5 in our population. Corresponding CRL measurements are 18mm and 64mm in the INTERGROWTH size chart, and 21mm and 63,5mm in Robinson's growth curve. When comparing our measurements to INTERGROWTH-21, we find parallel shifted curves where the fetuses in our study are estimated to be 3-4mm longer in both GW 8+5 and 12+5, corresponding to two days higher estimated fetal age at both measurements. Our growth curve is comparable to Roninson's curve in GW 8+5, but not in GW 12+5 (see figure 1). This study indicates a larger fetal size in the first trimester for pregnancies conceived by ART compared to those who are naturally conceived. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.