Table 2. Hazard ratios (HRs) with 95% confidence intervals (CIs) for any psychiatric disorder among twins after loss of a co-twin at birth, derived from different Cox models and by subtypes of psychiatric disorders.
| Population-based matched cohort | Twin-sibling family cohort | |||||
|---|---|---|---|---|---|---|
| Number of cases (crude incidence rate, per 1000 person years), exposed twins/unexposed twins | HR (95% CI)* | Number of cases (crude incidence rate, per 1000 person years), exposed twins/matched singletons | HR (95% CI)* | Number of cases (crude incidence rate, per 1000 person years), exposed twins/full siblings | HR (95% CI)* | |
| Model information: Model 1 Controlled for attained age, (as underlying time scale), sex, and birth characteristics (i.e., GA, birth weight for GA, maternal age at birth) |
178 (12.08)/600 (7.76) | 1.59 (1.33–1.90) | 178 (12.08)/723 (9.33) | 1.42 (1.19–1.68) | 130 (12.32)/130 (8.17) | 1.44 (0.83–2.51) |
| Model 2 above + neonatal factors (Apgar score) |
1.57 (1.31–1.87) | 1.37 (1.15–1.63) | 1.43 (0.82–2.49) | |||
| Model 3 above + family history of psychiatric disorders, maternal educational level, maternal cohabitation status |
1.56 (1.30–1.87) | 1.41 (1.19–1.69) | - | |||
| Full adjusted HRs† for subtypes of psychiatric disorders | ||||||
| Neurodevelopmental disorders (ADHD, ASD, and intellectual disabilities) | 71 (4.53)/224 (2.80) | 1.56 (1.16–2.08) | 71 (4.53)/270 (3.34) | 1.44 (1.09–1.92) | 52 (4.58)/35 (2.10) | 0.24 (0.05–1.30) |
| Emotional disorders (depression, anxiety, stress-related disorders) | 105 (6.75)/293 (3.67) | 1.90 (1.49–2.42) | 105 (6.75)/386 (4.82) | 1.57 (1.25–1.98) | 79 (7.04)/85 (5.21) | 1.75 (0.89–3.44) |
| Other psychiatric disorders | 84 (5.43)/310 (3.92) | 1.32 (1.02–1.70) | 84 (5.43)/361 (4.54) | 1.28 (1.00–1.64) | 60 (5.39)/61 (3.72) | 1.37 (0.61–3.08) |
ADHD, attention deficit hyperactivity disorder; ASD, autism spectrum disorder; GA,gestational age.
*Cox regression models were stratified by matching identifiers or family identifier, and adjusted for covariates mentioned in the ‘model information’ column. Attained age was applied as the underlying time scale.
†HRs were derived from fully adjusted Cox regression models, that is, model 3.