First-trimester growth rate in relation to selective fetal growth restriction in monochorionic twins

Introduction Crown–rump length discrepancy (CRLd) is commonly used to predict selective fetal growth restriction (sFGR) in monochorionic (MC) twins, but its predictive value is limited. This study aims to determine whether a first-trimester growth rate (GR) variable is associated with later sFGR. Methods Retrospective cohort including MC-twin pregnancies with first-trimester ultrasound data. CRLd was calculated for each fetus dividing the delta CLR by the bigger CRL; GR was calculated for each fetus dividing CRL by gestational age. Pregnancies were classified as normal and sFGR. Generalized estimating equations was used to evaluate the independent associations of GR and CRLd with sFGR. Results Among 335 pregnancies, 235 (70.1%) were normal, 100 (29.85%) were sFGR. GR was lower in pregnancies that developed sFGR and differed within sFGR pairs. Pearson's correlation showed no significant relationship between GR and CRLd. After accounting for co-twin correlation, both lower GR and higher CRLd were independently associated with higher odds of sFGR. Conclusion Reduced first-trimester GR and increased CRLd are independent early indicators of sFGR, and their combined assessment yields the best model fit.