Table 4.
Gestational age-specific rates of neonatal death/severe morbidity by subtype of preterm birth, Washington State, USA, 2004–2013
| Gestational age category and preterm birth subtype | Neonatal death/severe morbidity | Adjusted odds ratio per 1 year change* (95% CI) |
||
| N (per 100 live births) | Rate ratio (95% CI) |
|||
| 2004–2006 | 2011–2013 | |||
| 24–27 weeks | ||||
| PPROM | 133 (73.5) | 98 (75.4) | 1.03 (0.79 to 1.33) | 1.01 (0.94 to 1.10) |
| Spontaneous labour | 89 (65.9) | 142 (75.1) | 1.14 (0.87 to 1.49) | 1.09 (1.01 to 1.17) |
| Clinician-initiated | 131 (75.7) | 189 (67.7) | 0.89 (0.72 to 1.12) | 0.93 (0.87 to 0.99) |
| 28–31 weeks | ||||
| PPROM | 101 (34.2) | 112 (42.4) | 1.24 (0.95 to 1.62) | 1.07 (1.02 to 1.13) |
| Spontaneous labour | 112 (31.4) | 144 (34.6) | 1.10 (0.86 to 1.41) | 1.02 (0.98 to 1.08) |
| Clinician-initiated | 170 (35.2) | 240 (35.5) | 1.01 (0.83 to 1.23) | 1.02 (0.98 to 1.06) |
| 32–33 weeks | ||||
| PPROM | 42 (11.0) | 90 (22.0) | 2.00 (1.39 to 2.88) | 1.12 (1.06 to 1.19) |
| Spontaneous labour | 60 (11.3) | 87 (13.4) | 1.19 (0.85 to 1.65) | 1.01 (0.96 to 1.07) |
| Clinician-initiated | 64 (11.5) | 125 (15.8) | 1.37 (1.02 to 1.86) | 1.04 (0.99 to 1.08) |
| 34–36 weeks | ||||
| PPROM | 67 (3.5) | 129 (7.7) | 2.20 (1.64 to 2.96) | 1.13 (1.08 to 1.18) |
| Spontaneous labour | 111 (1.9) | 245 (4.4) | 2.32 (1.85 to 2.90) | 1.09 (1.06 to 1.13) |
| Clinician-initiated | 129 (2.8) | 265 (5.7) | 2.04 (1.65 to 2.51) | 1.10 (1.07 to 1.13) |
| All (24–36 weeks) | ||||
| PPROM | 343 (12.4) | 429 (17.3) | 1.40 (1.21 to 1.61) | 1.10 (1.07 to 1.13) |
| Spontaneous labour | 372 (5.5) | 618 (9.1) | 1.65 (1.45 to 1.88) | 1.06 (1.04 to 1.09) |
| Clinician-initiated | 494 (8.6) | 819 (12.9) | 1.50 (1.34 to 1.68) | 1.05 (1.03 to 1.07) |
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 neonatal death and/or morbidity.
*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; PPROM, preterm premature rupture of membranes; PVL, periventricular leukomalacia; ROP, retinopathy of prematurity; SGA, small-for-gestational age.