Table 4.

Odds ratios for physician-diagnosed AD by birth season stratified by maternal allergic history and sex

Season of birth	Case	Subtotal	Prevalence	cOR (95% CI)	aOR (95% CI)
Boys without maternal history of allergic disease (n = 20,715)
Spring (Apr–Jun)	169	4,925	3.4%	Reference	Reference
Summer (Jul–Sep)	205	6,105	3.4%	0.98 (0.80–1.20)	0.98 (0.79–1.22)
Autumn (Oct–Dec)	231	5,102	4.5%	1.34 (1.09–1.63)	1.25 (1.01–1.55)
Winter (Jan–Mar)	157	4,583	3.4%	1.00 (0.80–1.25)	0.95 (0.75–1.19)
Girls without maternal history of allergic disease (n = 19,689)
Spring (Apr–Jun)	101	4,632	2.2%	Reference	Reference
Summer (Jul–Sep)	120	5,702	2.1%	0.96 (0.74–1.26)	0.96 (0.72–1.26)
Autumn (Oct–Dec)	145	4,970	2.9%	1.35 (1.04–1.74)	1.29 (0.99–1.69)
Winter (Jan–Mar)	70	4,385	1.6%	0.73 (0.54–0.99)	0.72 (0.52–0.98)
Boys with maternal history of allergic disease (n = 20,981)
Spring (Apr–Jun)	279	4,933	5.7%	Reference	Reference
Summer (Jul–Sep)	444	6,055	7.3%	1.32 (1.13–1.54)	1.36 (1.15–1.60)
Autumn (Oct–Dec)	399	5,271	7.6%	1.37 (1.17–1.60)	1.37 (1.16–1.62)
Winter (Jan–Mar)	297	4,722	6.3%	1.12 (0.95–1.33)	1.16 (0.97–1.38)
Girls with maternal history of allergic disease (n = 19,816)
Spring (Apr–Jun)	180	4,573	3.9%	Reference	Reference
Summer (Jul–Sep)	262	5,683	4.6%	1.18 (0.97–1.43)	1.20 (0.98–1.48)
Autumn (Oct–Dec)	251	5,033	5.0%	1.28 (1.05–1.56)	1.34 (1.09–1.64)
Winter (Jan–Mar)	164	4,527	3.6%	0.92 (0.74–1.14)	0.97 (0.78–1.22)

Adjusted for maternal age, annual household income, maternal educational level, maternal intake of vitamin D during pregnancy, maternal active smoking during pregnancy, maternal passive smoking during pregnancy, gestational weeks, feeding method, presence of older siblings, pet ownership, and registered regional center. Bold letters indicate statistically significant differences calculated using the Benjamini–Hochberg method

Abbreviations: cOR Crude odds ratio, aOR Adjusted odds ratio, 95% CI 95% Confidence interval