Preterm subtypes by immigrants’ length of residence in Norway: a population-based study

Table 5 Adjusted relative risk (RR) of preterm delivery (PTD) and subtypes among immigrants (n = 40 709)

	PTD		Spontaneous PTD^a		Non-spontaneous PTD^b
	Adjusted demographic factors^c	Adjusted demographic^cand health factors^d	Adjusted demographic factors^c	Adjusted demographic^cand health factors^d	Adjusted demographic factors^c	Adjusted demographic^cand health factors^d
	aRR [95% CI]	aRR [95% CI]	aRR [95% CI]	aRR [95% CI]	aRR [95% CI]	aRR [95% CI]
Length of residence (years)
0-4 (Reference)	1.00	1.00	1.00	1.00	1.00	1.00
5-9	0.97 [0.88-1.06]	0.93 [0.85-1.02]	0.90 [0.80-1.01]	0.89 [0.80-1.00]	1.15 [0.96-1.38]	1.05 [0.88-1.25]
10-14	1.00 [0.88-1.14]	0.93 [0.83-1.05]	0.86 [0.74-1.00]	0.83 [0.72-0.97]	1.43 [1.15-1.78]	1.17 [0.94-1.67]
≥15	1.22 [1.08-1.38]	1.10 [0.98-1.24]	1.07 [0.92-1.24]	1.03 [0.90-1.20]	1.68 [1.34-2.10]	1.28 [1.02-1.61]
P trend	0.012	0.391	0.883	0.516	<0.001	0.018
Country of birth
Iraq (Reference)	1.00	1.00	1.00	1.00	1.00	1.00
Pakistan	1.29 [1.12-1.48]	1.26 [1.10-1.45]	1.16 [0.99-1.37]	1.20 [1.02-1.42]	1.57 [1.21-2.04]	1.37 [1.06-1.76]
Phillippines	1.41 [1.22-1.64]	1.32 [1.14-1.53]	1.48 [1.24-1.76]	1.43 [1.19-1.70]	1.25 [0.94-1.68]	1.08 [0.81-1.44]
Somalia	0.95 [0.82-1.10]	0.89 [0.77-1.03]	0.82 [0.69-0.98]	0.82 [0.68-0.98]	1.26 [0.97-1.64]	1.07 [0.83-1.38]
Sri Lanka	1.31 [1.13-1.52]	1.29 [1.11-1.50]	1.32 [1.10-1.58]	1.34 [1.11-1.60]	1.27 [0.95-1.69]	1.20 [0.90-1.59]
Vietnam	1.26 [1.09-1.46]	1.38 [1.19-1.59]	1.53 [1.28-1.81]	1.60 [1.35-1.89]	0.64 [0.47-0.89]	0.81 [0.59-1.12]

^aSpontaneous PTD included births <37 completed gestational weeks with spontaneous labor onset or with prelabour rupture of membranes.
^bNon-spontaneous PTD included births <37 completed gestational weeks with onset by inducted labor or by cesarean section.
^cDemographic factors included the length of residence, country of birth, year of delivery, maternal age at delivery, parity and size of labor unit.
^dHealth factors included gestational and pre-gestational diabetes, hypertensive disorders, placenta disorders, major birth defects, maternal smoking and small- and large-for-gestational age infants.
Bold text indicates significant difference relative to the reference.

ISSN: 1471-2393