Table 3.

Effect modification of maternal use of any thermoregulation-related (Level 3) medications^a during the period from the month before pregnancy through the end of the 1st trimester on the association between a summertime EHE90 in the residential area during the maternal critical period and CHDs among offspring in eight states, NBDPS, 1997–2007.

Climate Region	No medication use		Medication use reported		Multiplicative scale	Additive scale
	N of Cases exp/unexp	aOR# (95% CI)	N of Cases exp/unexp	aORb (95% CI)	P value	ICR
Overall	604/456	0.92 (0.77, 1.09)	586/424	0.92 (0.77, 1.11)	0.97	−0.02 (−0.28, 0.25)
South (AR, TX)	160/176	0.70 (0.51, 0.97)	148/151	0.69 (0.49, 0.98)	0.98	−0.02 (−0.45, 0.41)
Southeast (NC, GA)	104/116	0.92 (0.63, 1.33)	126/122	1.03 (0.72, 1.48)	0.63	0.13 (−0.40, 0.66)
Northeast (NY)	46/64	1.09 (0.66, 1.80)	59/50	1.39 (0.81, 2.41)	0.66	0.27 (−0.64, 1.18)
Southwest (UT)	90/17	0.58 (0.25, 1.33)	98/20	1.26 (0.63, 2.55)	0.18	0.59 (−0.05, 1.23)
West (CA)	153/38	1.17 (0.72, 1.90)	91/27	0.88 (0.47, 1.67)	0.45	−0.37 (−1.50, 0.76)
Midwest (IA)	51/45	0.95 (0.56, 1.62)	64/54	0.73 (0.46, 1.18)	0.35	−0.35 (−1.17, 0.46)

Abbreviation: aOR, adjusted odds ratio; AR, Arkansas; CA, California; CHD, congenital heart defects; CI, confidence interval; EHE, extreme heat event; EHE90, EHE was defined using the 90^th percentile of daily maximum temperature for each study region during postconceptional weeks 3–8; GA, Georgia; IA, Iowa; ICR, interaction contrast ratio; NBDPS, National Birth Defects Prevention Study; NC, North Carolina; NY, New York; TX, Texas; UT, Utah.

^aExposure to medication was defined as self-reported use at least once at any point during the month before conception through the end of the first trimester.

^bReference group was participants unexposed to both EHE90 and medication use; adjusted for maternal age (continuous), maternal race/ethnicity, and maternal education level.