The following is a summary of “Clinical implications of crown-rump length discordance at 11 to 14 weeks in dichorionic twins,” published in the January 2024 issue of Obstetrics and Gynecology by Janssen, et al.

Crown-rump length (CRL) discordance, characterized by a difference of ≥10% in measurements, has been explored as an early sonographic indicator for subsequent growth abnormalities and is associated with a heightened risk of fetal loss in twin pregnancies. However, prior studies have not extensively investigated the prevalence of fetal aneuploidy or structural anomalies in twins with discordance, nor have they independently assessed the association of CRL discordance with adverse perinatal outcomes. Additionally, there is limited data regarding the efficacy of cell-free DNA screening for aneuploidy in dichorionic twins with CRL discordance. For a study, researchers sought to determine whether CRL discordance in dichorionic twins between 11 and 14 weeks of gestation correlates with a higher risk of aneuploidy, structural anomalies, or adverse perinatal outcomes. Furthermore, they aimed to assess the performance of cell-free DNA screening in dichorionic twin pregnancies with CRL discordance.

The secondary analysis utilized data from a multicenter retrospective cohort study conducted from December 2011 to February 2020, focusing on the performance of cell-free DNA screening for common trisomies in twin pregnancies. Live dichorionic pregnancies with CRL measurements between 11 and 14 weeks of gestation were included. Firstly, twin pregnancies with discordant CRLs were compared with those with concordant CRLs, assessing the prevalence of aneuploidy and fetal structural anomalies in either twin. Secondly, the prevalence of a composite adverse perinatal outcome, including preterm birth at <34 weeks, hypertensive disorders of pregnancy, stillbirth or miscarriage, small-for-gestational-age birthweight, and birthweight discordance, were compared. Additionally, the performance of cell-free DNA screening in pregnancies with and without CRL discordance was evaluated. Multivariable regression was used to adjust for confounders when comparing outcomes.

Out of 987 dichorionic twins analyzed, 142 (14%) exhibited crown-rump length (CRL) discordance. Twins with CRL discordance had a notably higher prevalence of aneuploidy than those with concordant CRL measurements (9.9% vs 3.9%, respectively; adjusted relative risk: 2.7; 95% CI: 1.4–4.9). Similarly, the occurrence of structural anomalies (adjusted relative risk: 2.5; 95% CI: 1.4–4.4) and composite adverse perinatal outcomes (adjusted relative risk: 1.2; 95% CI: 1.04–1.3) was significantly elevated in twins with discordant CRLs. Furthermore, stratified analysis revealed increased risks of aneuploidy (adjusted relative risk: 3.5; 95% CI: 1.5–8.4) and structural anomalies (adjusted relative risk: 2.7; 95% CI: 1.5–4.8) in twins with CRL discordance, even in the absence of other ultrasound markers. Cell-free DNA screening demonstrated high negative predictive values for trisomy 21, trisomy 18, and trisomy 13, irrespective of CRL discordance, with only 1 false-negative result observed for trisomy 21 in a twin pregnancy with discordance.

The presence of crown-rump length discordance in dichorionic twins was associated with an increased risk of aneuploidy, structural anomalies, and adverse perinatal outcomes, even without additional sonographic abnormalities. While cell-free DNA screening exhibited high sensitivity and negative predictive values regardless of CRL discordance, one false-negative result underscores the need for diagnostic testing in certain cases. The findings provided valuable insights into identifying twin pregnancies that may benefit from enhanced screening and surveillance, particularly in cases where early sonographic markers may not be conclusive.

Reference: ajog.org/article/S0002-9378(23)00501-X/abstract