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Faculty have requested this content not be shared on social media
CME Credit Offered
CME Credit Offered
Abstract Award
Abstract Award
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Poster Session 1

(201) First versus early second trimester dating: accuracy in predicting small for gestational age neonates

Thursday, January 30, 2025
10:30 AM – 12:30 PM  
Objective: While “optimal” pregnancy dating is defined as any ultrasound confirmation prior to 22 weeks, evaluation in the first trimester may provide a more accurate assessment of gestational age (GA). This is important when early fetal growth restriction (FGR) is detected, as inaccurate dating can cause a false positive diagnosis. We sought to compare the accuracy of FGR in predicting small for gestational age (SGA) using first versus early second trimester dating.

Study Design: We conducted a multi-center observational study of singleton pregnancies with FGR (EFW < 10th percentile) diagnosed during a 16-24 week anatomy scan between 1/2016 and 12/2021. Pregnancies with estimated date of delivery (EDD) confirmed by first trimester ultrasound were compared to those with dating confirmation in early second trimester (between 14 and 22 weeks). Cases with suspected anatomic, genetic, or infectious etiologies of FGR were excluded. The primary outcome was SGA at birth (< 10th percentile for gestational age). Secondary outcomes were GA at delivery, hypertensive disorders of pregnancy (HDP), mode of delivery, indicated preterm delivery, and a composite of adverse neonatal outcomes. Data were analyzed using Pearson’s Chi-Square (Fisher’s-Exact) and Mann-Whitney U tests.

Results: Of 385 cases of FGR, 319 (83%) had dating confirmation in first trimester and 66 (17%) in the early second trimester. The prevalence of SGA was similar between groups with 30% in the first trimester cohort and 26% in the early second trimester cohort (p=0.24). Both groups had a similar median GA at delivery, and similar rates of medically indicated preterm delivery, HDP, and composite neonatal morbidity.

Conclusion: In pregnancies with FGR, first trimester dating confirmation was not superior to early second trimester dating in predicting SGA. This lends support to the current definition of optimal dating utilized by the American College of Obstetricians and Gynecologists. Future studies with a larger second-trimester dating cohort as well as FGR diagnosed later in pregnancy would help further validate these findings.