Insecure attachment and internalizing behavior problems in growth discordant identical twins.

Background: Psychosocial development in monochorionic (MC) twins born after selective fetal growth restriction (sFGR) has been unreported to date, despite its importance for daily functioning and future relationships.

Aims: To investigate psychosocial development, attachment and school functioning in MC twins with sFGR and compare outcomes with the general population and between smaller and larger twins.

Study Design: Observational cohort study.

Subjects: MC twins with sFGR (defined as a birth weight discordance ≥20 %) born between 2002 and 2017 and aged 3-17 years.

Outcome Measures: Multiple parent report questionnaires: the Child Behavior Checklist (social-emotional development and behavior), the (Early) Childhood Behavior Questionnaire Very Short Form (temperament), the Attachment Insecurity Screening Inventory (attachment) and a school functioning questionnaire.

Results: Median age for the 48 twin pairs was 11 (interquartile range (IQR) 8-13) years. Attachment insecurity for both twins was higher than in the general population for ambivalence/resistance (34 % (21/62) vs. 16 %, p = 0.024) and total attachment insecurity (35 % (22/62) vs. 16 %, p = 0.016). Smaller twins had more internalizing behavioral problems, i.e. negative emotions and behaviors turned inwards (22 % (10/46) vs. 11 % (5/46), p = 0.021) and a higher negative affect, i.e. more likely to experience negative emotions (3.2 (2.9-3.7) vs. 2.9 (2.2-3.2), p = 0.009) than larger twins, as well as a lower secondary school level (p = 0.031).

Conclusion: MC twins with sFGR have more ambivalent/resistant attachment insecurity following the complicated pregnancy course. Smaller twins have a tendency towards negative emotions and internalizing behaviors compared to larger twins, indicating an increased sensitivity for depression and anxiety.