Neurodevelopmental outcomes at 2 years corrected age of preterm Vietnamese infants compared with healthy Vietnamese infants
| Neurodevelopmental domains | Preterm Vietnamese infants (n=184) | Healthy Vietnamese infants* (n=78) | Mean difference (95% CI) | P value† | Effect size Cohen’s d | |
| Cognitive composite score | Mean (SD) | 84.5 (8.6) | 91.4 (7.5) | −6.9 (−9.1 to −4.7) | <0.001 | 0.83 |
| (n=184) | Z-score, mean (SD)‡ | −0.91 (1.13) | – | |||
| <−2 SDs, n (%) | 32/184 (17%) | – | ||||
| Language composite score | Mean (SD) | 88.7 (12.5) | 95.9 (11.9) | −7.2 (−10.5 to −3.8) | <0.001 | 0.58 |
| (n=179) | Z-score, mean (SD) | −0.60 (1.05) | – | |||
| <−2 SDs, n (%) | 14/179 (8%) | – | ||||
| Motor composite score | Mean (SD) | 93.1 (9.0) | 96.8 (9.3) | −3.7 (−6.1 to −1.2) | 0.003 | 0.40 |
| (n=180) | Z-score, mean (SD) | −0.39 (0.96) | – | |||
| <−2 SDs, n (%) | 8/180 (4%) | – | ||||
| Cognitive subtest | Mean (SD) | 6.9 (1.7) | 8.3 (1.5) | −1.4 (−1.8 to −0.9) | <0.001 | 0.83 |
| (n=184) | Z-score, mean (SD) | 0.91 (1.13) | – | |||
| <−2 SDs, n (%) | 32/184 (17%) | – | ||||
| Receptive language subtest | Mean (SD) | 7.7 (2.0) | 8.9 (2.1) | −1.2 (−1.7 to −0.6) | <0.001 | 0.57 |
| (n=179) | Z-score, mean (SD) | −0.56 (0.78) | – | |||
| <−2 SDs, n (%) | 13/179 (7%) | – | ||||
| Expressive language subtest | Mean (SD) | 8.3 (2.7) | 9.6 (2.1) | −1.3 (−2.0 to −0.6) | <0.001 | 0.50 |
| (n=179) | Z-score, mean (SD) | −0.55 (1.13) | – | |||
| <−2 SDs, n (%) | 11/179 (6%) | – | ||||
| Fine motor subtest | Mean (SD) | 8.6 (1.9) | 9.6 (1.8) | −1.1 (−1.6 to −0.6) | <0.001 | 0.56 |
| (n=183) | Z-score, mean (SD) | −0.60 (1.10) | – | |||
| <−2 SDs, n (%) | 19/183 (10%) | – | ||||
| Gross motor subtest | Mean (SD) | 9.0 (1.9) | 9.2 (2.1) | −0.2 (−0.8 to 0.3) | 0.37 | 0.12 |
| (n=180) | Z-score, mean (SD) | −0.11 (0.86) | – | |||
| <−2 SDs, n (%) | 3/180 (2%) | – | ||||
The Bayley-III generates a raw score that is converted to a scale score and then combined to yield a composite score. It consists of five subscale scores: cognitive, receptive language, expressive language, fine motor and gross motor and three composite scores: cognitive, language and motor composite scores, with the lower scores indicating a greater degree of developmental delay.
*Healthy Vietnamese infants were born full-term, without history of severe illness (cardiac, epilepsy and HIV), without intensive care admission, and without known developmental delay.
↵†Student’s t-test was used to compare Bayley-III scores between preterm and healthy Vietnamese infants.
↵‡Bayley-III Z-scores of preterm infants were calculated using mean and SD of Bayley-III scores of healthy Vietnamese infants.