Table 3.

Gestational age-specific rates of neonatal death by subtype of preterm birth, Washington State, USA, 2004–2013

Gestational age category and preterm birth subtype	Neonatal death			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	27 (14.9)	18 (13.9)	0.93 (0.51 to 1.69)	1.05 (0.94 to 1.17)
Spontaneous labour	21 (15.6)	26 (13.8)	0.88 (0.50 to 1.57)	0.95 (0.86 to 1.06)
Clinician-initiated	28 (16.2)	41 (14.7)	0.91 (0.56 to 1.47)	0.94 (0.86 to 1.03)
28–31 weeks
PPROM	14 (4.8)	5 (1.9)	0.40 (0.14 to 1.10)	0.92 (0.78 to 1.07)
Spontaneous labour	11 (3.1)	9 (2.2)	0.71 (0.30 to 1.71)	0.91 (0.77 to 1.06)
Clinician-initiated	30 (6.2)	26 (3.8)	0.61 (0.36 to 1.04)	0.96 (0.88 to 1.06)
32–33 weeks
PPROM	2 (0.5)	5 (1.2)	2.40 (0.47 to 12.37)	1.08 (0.80 to 1.45)
Spontaneous labour	7 (1.3)	5 (0.8)	0.62 (0.20 to 1.94)	0.97 (0.83 to 1.13)
Clinician-initiated	14 (2.5)	8 (1.0)	0.40 (0.17 to 0.95)	0.85 (0.74 to 0.97)
34–36 weeks
PPROM	14 (0.7)	7 (0.4)	0.57 (0.23 to 1.42)	0.97 (0.84 to 1.12)
Spontaneous labour	7 (0.1)	22 (0.4)	4.00 (1.71 to 9.36)	1.08 (0.96 to 1.20)
Clinician-initiated	22 (0.5)	35 (0.8)	1.60 (0.94 to 2.73)	1.10 (1.01 to 1.20)
All (24 –36 weeks)
PPROM	57 (2.1)	35 (1.4)	0.67 (0.44 to 1.02)	1.00 (0.93 to 1.07)
Spontaneous labour	46 (0.7)	62 (0.9)	1.29 (0.88 to 1.88)	0.98 (0.92 to 1.04)
Clinician-initiated	94 (1.6)	110 (1.7)	1.06 (0.81 to 1.40)	0.98 (0.94 to 1.03)

Adjusted odds ratios express the average annual change in the odds of neonatal death.

*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.

PPROM, preterm premature rupture of membranes.