Table 2.

Crude and adjusted hazard ratios^* (HRs) of fetal death^† (n=492) among 113,331 women who gave birth to singletons in Norway in 2009 or 2010, according to influenza vaccination status and being pregnant during the pandemic ^‡, with or without a clinical diagnosis of influenza.

	Pregnancy	Crude		Adjusted□		Adjusted¶
	days at risk§	HR	(95% CI)	HR	(95% CI)	HR	(95% CI)
Total	18,970,404
Vaccinated in pregnancy
No	15,942,324	1		1		1
Yes	3,028,152	0.95	(0.74 – 1.21)	0.84	(0.64 – 1.10)	0.88	(0.66 – 1.17)
Pregnant during the pandemic
No	10,422,035	1		1		1
Yes	8,548,369	1.15	(0.96 – 1.37)	1.21	(1.00 – 1.48)	1.26	(1.02 – 1.55)
Pregnant during the pandemic
No	10,422,035	1		1		1
Yes, without a influenza diagnosis	8,221,514	1.11	(0.93 – 1.33)	1.18	(0.96 – 1.44)	1.23	(0.99 – 1.52)
Yes, with a influenza diagnosis	326,855	2.00	(1.20 – 3.32)	2.10	(1.27 – 3.49)	1.91	(1.07 – 3.41)

^*Hazard ratios were estimated with gestational day as the time metric.

^†Any fetal death/stillbirth after 12 completed pregnancy weeks.

^‡At least one day in pregnancy between 1 October and 31 December 2009.

^§Each woman may contribute days at risk as both unexposed and exposed.

^□Vaccination status adjusted for being pregnant during the main pandemic wave (Yes/No) but not for other covariates. Influenza exposures adjusted for vaccination status but not for other covariates.

^¶Adjusted for age, parity, marital status, use of nutritional supplements in pregnancy, smoking in pregnancy, history of earlier fetal death, and chronic health conditions (asthma, hypertension, kidney disease, rheumatoid arthritis, epilepsy, thyroid disease, or diabetes).