Uncomplicated monochorionic twins: neurodevelopmental insights and implications

Emerging evidence indicates that uncomplicated monochorionic diamniotic (MCDA) twins deviate physiologically from singletons, probably owing to adaptations to their unique intrauterine environment. However, their long-term neurodevelopmental outcomes remain poorly understood. Early identification of neurodevelopmental risks is critical to optimize neuroplasticity during key developmental periods. The aim of this study was to assess neurodevelopmental outcomes in uncomplicated MCDA twins up to 3 years of age and propose recommendations for future research and follow-up protocols.

This was an observational cohort study of uncomplicated MCDA twins born between January 2015 and January 2022 at a tertiary care center in Italy, which agreed to follow-up. Inclusion criteria included gestational age at birth ≥ 34 weeks and an uncomplicated pregnancy. Neurodevelopmental assessments were performed at 1, 2 and 3 years of age using Bayley Scales of Infant and Toddler Development third edition and neurological evaluations. The primary outcome was the presence and severity of neurodevelopmental impairment (NDI). Crude and multivariable multinomial logistic regression models were used to evaluate associations between NDI (mild or severe) and perinatal or environmental factors, adjusting for familial clustering.

Among 138 MCDA twins (69 pregnancies) included in the study, mean Bayley scores were comparable with those of infants from singleton pregnancies. Forty (29.0%) infants had mild NDI and eight (5.8%) had severe NDI. Sixteen (11.6%) infants were diagnosed with behavioral disorders, including eight with autism spectrum disorder (ASD) and eight with emotional dysregulation. Respiratory distress syndrome was the strongest predictor of mild NDI (odds ratio, 4.60 (95% CI, 1.37-15.1)). Female sex of the twin, higher maternal age and higher sociocultural status were associated with a lower risk of mild NDI. Higher maternal age and sociocultural level were also linked to a lower risk of severe NDI.

Despite generally favorable outcomes, mild neurodevelopmental impairment is common in uncomplicated MCDA twins, with a higher incidence of ASD. Early detection is crucial to mitigate long-term impact. A standardized neurodevelopmental follow-up protocol extending through school age is recommended. © 2025 International Society of Ultrasound in Obstetrics and Gynecology.