Gestational age-specific rates of adverse neonatal outcomes among singleton preterm infants, Washington State, USA, 2004–2013
| Outcome and gestational age category | Rates per 100 live births | Adjusted odds ratio per 1 year change* (95% CI) | ||
| N (Rate) | Rate ratio (95% CI) | |||
| 2004–2006 | 2011–2013 | |||
| Neonatal death | ||||
| 24–27 weeks | 76 (15.5) | 85 (14.2) | 0.92 (0.67 to 1.25) | 0.97 (0.92 to 1.03) |
| 28–31 | 55 (4.9) | 40 (3.0) | 0.61 (0.41 to 0.92) | 0.95 (0.89 to 1.01) |
| 32–33 | 23 (1.6) | 18 (1.0) | 0.63 (0.34 to 1.16) | 0.93 (0.84 to 1.02) |
| 34–36 | 43 (0.4) | 64 (0.5) | 1.25 (0.85 to 1.84) | 1.06 (1.00 to 1.13) |
| All (24–36) | 197 (1.3) | 207 (1.3) | 1.00 (0.82 to 1.22) | 0.99 (0.95 to 1.02) |
| Neonatal death/severe morbidity | ||||
| 24–27 weeks | 353 (72.2) | 429 (71.7) | 0.99 (0.86 to 1.14) | 1.00 (0.96 to 1.04) |
| 28–31 | 383 (33.7) | 496 (36.6) | 1.08 (0.95 to 1.24) | 1.03 (1.00 to 1.06) |
| 32–33 | 166 (11.3) | 302 (16.3) | 1.44 (1.19 to 1.74) | 1.05 (1.02 to 1.08) |
| 34–36 | 307 (2.5) | 639 (5.4) | 2.16 (1.89 to 2.47) | 1.10 (1.08 to 1.12) |
| All (24–36) | 1 209 (7.9) | 1 866 (11.9) | 1.51 (1.40 to 1.62) | 1.06 (1.05 to 1.08) |
Severe morbidity includes BPD, IVH grade ≥3, PVL, ROP, NEC, neonatal sepsis, convulsions of newborn and severe birth trauma.
Adjusted odds ratios express the average annual change in the odds of the outcome.
*Calendar year was modelled as a continuous variable; adjusted for temporal changes in maternal age, BMI, race, education, smoking, marital status, parity, chronic hypertension, pre-pregnancy diabetes, assisted conception, health insurance provider, gestational age, SGA infant, sex and congenital anomalies.
BMI, body mass index; BPD, bronchopulmonary dysplasia; IVH, intraventricular haemorrhage; NEC, necrotising enterocolitis; PVL, periventricular leukomalacia; ROP, retinopathy of prematurity; SGA, small-for-gestational age.