. Author manuscript; available in PMC: 2016 Mar 30.

Published in final edited form as: Paediatr Perinat Epidemiol. 2014 Oct 21;28(6):498–509. doi: 10.1111/ppe.12152

Table 2.

Association of influenza vaccination during pregnancy with the risks of preterm delivery (PTD) and small for gestational age (SGA) among mothers of non-malformed infants

	All		PTD^b		Unadjusted		Adjusted^c

Influenza vaccination timing^a	n	%	n	%	HR	[95% CI]	HR	[95% CI]
All	1595	100.0	107	6.7
None	1285	80.6	83	6.5
Anytime during pregnancy	310	19.4	24	7.7	1.30	[0.83, 2.05]	1.37	[0.84, 2.23]
First trimester	82	5.1	4	4.9	0.74	[0.27, 2.02]	0.66	[0.22, 1.97]
Second trimester	138	8.7	13	9.4	1.49	[0.83, 2.67]	1.46	[0.75, 2.84]
Third trimester	90	5.6	7	7.8	1.55	[0.71, 3.36]	1.53	[0.66, 3.56]

	All		SGA^d		Unadjusted Adjusted^c		Adjusted

	n	%	n	%	OR	[95% CI]	OR	[95% CI]

All	1619	100.0	172	10.6
None	1285	79.4	142	11.1
Anytime during pregnancy	334	20.6	30	9.0	0.79	[0.53, 1.20]	1.03	[0.66, 1.62]
First trimester	82	5.1	4	4.9	0.41	[0.11, 1.13]	0.44	[0.15, 1.29]
Second trimester	138	8.5	16	11.6	1.06	[0.61, 1.83]	1.53	[0.81, 2.88]
Third trimester	114	7.0	10	8.8	0.77	[0.40, 1.52]	1.00	[0.48, 2.09]

Represents the unvaccinated and the vaccinated against seasonal influenza only; 385 vaccinated against pandemic H1N1 were excluded from the analysis (including 20 PTD and 32 SGA).

This represents the per cent preterm birth within our analytic cohort, not the risk of PTD among all women surveyed during study years (7.2 %;153/2136).

Adjusted for propensity score.

This represents the per cent SGA within our analytic cohort, not the prevalence of SGA among all women surveyed during study years (10.6 %; 232/2136).

PTD, preterm delivery; HR, hazard ratio; CI, confidence interval; OR, odds ratio; SGA, small for gestational age according to reference birthweight percentiles.