Adverse neonatal outcomes in small‐for‐gestational age twins identified using twin vs singleton growth charts: systematic review and meta‐analysis

Objective: To evaluate the use of twin vs singleton growth charts for detecting small-for-gestational-age (SGA) twins at risk of adverse neonatal outcomes. Methods: MEDLINE, EMBASE, CINAHL, Cochrane and Scopus databases were searched electronically from inception to May 2024. The primary outcome of this meta-analysis was the risk of composite adverse neonatal outcome in SGA fetuses in a twin pregnancy diagnosed using twin or singleton charts. The secondary outcomes included: neonatal intensive care unit (NICU) admission, oxygen supplementation or continuous positive airway pressure, mechanical ventilation, respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, neonatal sepsis and neonatal mortality. Prospective and retrospective studies on neonatal outcomes of monochorionic or diamniotic twins diagnosed with SGA using both singleton and twin charts based on estimated fetal weight or birth weight were considered suitable for inclusion. Quality assessment of the included studies was performed using the Newcastle-Ottawa Scale for cohort studies. Random-effects head-to-head meta-analyses were used to analyze the data. Results: Six studies were included in the systematic review and five studies, including 10 554 twin pregnancies, were included in the meta-analysis. The risk of composite adverse neonatal outcome (OR, 3.11 (95% CI, 1.83-5.26)) and that of most secondary outcomes was significantly higher in SGA fetuses diagnosed using twin charts compared with those diagnosed using singleton charts. Conversely, the risk of composite adverse neonatal outcome (OR, 1.22 (95% CI, 0.73-2.04)) and most secondary outcomes was similar when comparing SGA fetuses diagnosed using singleton charts vs non-SGA fetuses diagnosed using twin charts, except for the risk of NICU admission, which was significantly higher in SGA fetuses diagnosed using singleton charts. When comparing non-SGA fetuses diagnosed using twin charts vs non-SGA fetuses diagnosed using singleton charts, the risk of composite adverse neonatal outcome was significantly lower when using twin charts (OR, 0.90 (95% CI, 0.83-0.97)). Finally, when comparing SGA vs non-SGA fetuses diagnosed using singleton charts, there was no significant difference for the primary or secondary outcomes, except for a higher risk of NICU admission in the SGA group (OR, 1.54 (95% CI, 1.11-2.12)). Twin charts had lower sensitivity than singleton charts in predicting adverse neonatal outcome (14% (95% CI, 7-26%) vs 32% (95% CI, 24-41%)), but higher specificity (95% (95% CI, 86-98%) vs 71% (95% CI, 63-77%)). Conclusions: Twin charts increase the specificity but reduce the sensitivity for the detection of SGA compared with singleton charts. Nevertheless, twin charts detect cases at higher risk of adverse neonatal outcome, which may be the cases that require intervention. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.