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Table 2 Analyses of inter-pregnancy intervals, Cox proportional hazards regression of time from one birth to next

From: Reproductive stoppage in autism spectrum disorder in a population of 2.5 million individuals

 Hazard ratio (95% confidence interval)
 All birth orders combinedBirth order specific
   First to secondSecond to third
 ASD in any previously bornASD in immediately previously bornASD in first-bornASD in first-bornASD in second-bornASD in both first- and second-born
Crude
 0.79 (0.78–0.80)1.05 (1.03–1.07)0.87 (0.86–0.89)1.08 (1.05–1.11)1.17 (1.13–1.22)1.05 (0.93–1.17)
Adjusted
 Birth ordera0.97 (0.96–0.99)0.94 (0.92–0.96)NANANANA
 Maternal age0.82 (0.81–0.83)1.01 (1.00–1.03)0.88 (0.87–0.90)1.09 (1.05–1.12)1.11 (1.08–1.15)1.06 (0.95–1.19)
 Birth period0.80 (0.79–0.81)1.04 (1.02–1.05)0.88 (0.86–0.89)1.09 (1.05–1.12)1.17 (1.13–1.21)1.06 (0.95–1.19)
 Sex0.78 (0.77–0.79)1.05 (1.03–1.06)0.87 (0.85–0.89)1.08 (1.05–1.11)1.17 (1.13–1.21)1.04 (0.93–1.17)
 Paternal age0.81 (0.8–0.82)1.03 (1.01–1.04)0.88 (0.86–0.89)1.09 (1.06–1.12)1.14 (1.10–1.18)1.08 (0.96–1.20)
 Maternal education0.79 (0.78–0.81)1.06 (1.05–1.08)0.88 (0.86–0.90)1.10 (1.06–1.13)1.18 (1.14–1.22)1.05 (0.94–1.17)
 All of abovea1.00 (0.99–1.02)0.97 (0.95–0.98)0.90 (0.88–0.91)1.12 (1.08–1.15)1.16 (1.12–1.20)1.11 (0.99–1.24)
  1. NA not applicable, ASD autism spectrum disorder
  2. aBirth order adjustment by stratification (stratified Cox), where applicable