Table 3.

Seroconversion Rates by Trimester and Postpartum Period

Time Period	Averaged Overall All Strains, All Years				Pandemic H1N1 Only
	n	% Seroconverted*	Odds Ratio† 95% CI	n	% Seroconverted*	Odds Ratio†† 95% CI
First trimester (less than 13 weeks)	73	54.8	0.48 (0.16, 1.41)	7	28.6	0.27 (0.03, 2.12)
Second trimester (13-less than 28 weeks)	183	62.8	0.76 (0.29, 2.05)	16	62.5	1.11 (0.22, 5.62)
Early third trimester (28-less than 34 weeks)	86	58.1	0.74 (0.26, 2.14)	10	60.0	1.00 (0.17, 5.98)
Late third trimester (34 weeks or more)	56	69.6	1.41 (0.43, 4.58)	8	87.5	4.67 (0.40, 53.95)
Immediate postpartum (less than 72 hours)	73	54.8	0.55 (0.18, 1.71)	3	66.7	Ref
Later postpartum (approximately 6 weeks)	36	69.4	ref	7	57.1

CI, confidence interval.

^*Crude seroconversion rate averaged over all strains and separately for pandemic H1N1

^†Adjusted for strain, baseline antibody titer, vaccination in the last year, age at vaccination, education, and obesity.

^††Unadjusted