ASQ-3 developmental outcomes at six months in a Bulgarian infant cohort: a cross-cultural comparison with U.S. norms

Early developmental screening relies heavily on U.S.-standardized normative benchmarks, raising questions about cross-cultural stability and the relative influence of biological vs. contextual factors during infancy. This study examined Ages and Stages Questionnaire (ASQ-3) outcomes at six months in a Bulgarian infant cohort in comparison with established U.S. norms.

In this cross-sectional study, 155 infants (six months chronological or corrected age) were assessed using the ASQ-3 during routine pediatric visits. One-sample t-tests were used to compare domain scores with U.S. normative means. Effect sizes (Cohen's d), 95% confidence intervals, and post hoc power sensitivity analyses were calculated. Secondary analyses evaluated the effects of birth weight, gestational age, and sex.

Cross-cultural comparisons showed statistically significant differences in Gross Motor (d = -0.28) and Problem Solving (d = 0.30); however, all effect sizes were small (|d| ≤ 0.30), with no moderate or large deviations observed. In contrast, infants with birth weight <2,500 g demonstrated moderate-to-large effects across multiple domains (d = -0.63 to -0.88), particularly in Gross Motor and Personal-Social functioning. Differences related to gestational age were not clinically meaningful after correction for age. A small female advantage was observed in Communication (d = 0.37).

ASQ-3 outcomes at six months suggest a high degree of cross-cultural similarity in this Southeastern European infant cohort. Variability in developmental outcomes in the present cohort appeared more strongly associated with biological risk factors than with cross-cultural contextual variation during early infancy. These findings support the use of ASQ-3 in the Bulgarian clinical context and highlight the importance of integrating perinatal risk factors into early developmental surveillance.