Fetal Growth in Pregnancies Conceived by Single Embryo Transfer: A Prospective Observational Cohort Study During Three Trimesters

Introduction The main aim is to describe fetal growth trajectories in pregnancies conceived by assisted reproductive technology (ART) from gestational week 12 until birth. The secondary aims are to compare ultrasound dating and transfer date estimations of gestational age and to describe birthweight. Materials The study population consists of 114 pregnant women following blastocyst transfer at St. Olavs hospital, Trondheim University Hospital, Norway, during the inclusion period from February 2022 to January 2024. Methods Ultrasound scans were performed 70, 112, 154, and 224 days after embryo transfer (ET) (gestational week 12 + 5, 18 + 5, 24 + 5 and 34 + 5). Crown‐rump length obtained at the first scan and biparietal diameter (BPD) from the second scan were used to calculate gestational age according to three different growth curves. We evaluated fetal growth across four timepoints with a linear mixed‐effects model. Data regarding pregnancy, birth, and neonatal outcomes were obtained from patient records. Results The within‐pregnancy correlation of BPD, mean abdominal diameter and femur length between the four examinations was relatively small (intraclass correlation 0.36, 0.31 and 0.33), indicating that intra‐pregnancy variation in fetal growth exceeds inter‐pregnancy variation. Ultrasound measurements suggested a gestational age 2 days older than ET‐based estimates. The growth difference between the study group and the normal population increased during pregnancy, reaching a difference in median birthweight of 120 g. Conclusion Fetuses conceived through ART show altered growth dynamics, with higher gestational age estimates based on ultrasound measurements compared to dating from ET. We found a higher median birthweight for pregnancies following ART compared with reference data from the general population.