Table 3.

Associations Between 1996 Log₁₀ TCDD Concentration (Parts per Trillion) and Thyroid Hormone Levels by Menarcheal Status at the Time of the Explosion (1976), Seveso Women's Health Study, Italy, 1976–2009

Thyroid Hormone	No. of Participantsa	Adjustedb βc	95% CI	Menarcheal Status at Explosion						P for Interaction
				Premenarche			Postmenarche
				No.	Adjustedb βc	95% CI	No.	Adjustedb βc	95% CI
1996 Thyroid Hormone Measurements
TSHd	260	−4.46	−18.89, 12.54	161	−8.94	−25.14, 10.75	99	−1.12	−26.48, 32.94	0.62
Total T4	251	−0.37	−0.90, 0.17	153	−0.54	−1.32, 0.20	98	−0.11	−0.85, 0.64	0.42
Free T4	251	−0.03	−0.16, 0.10	153	0.00	−0.14, 0.13	98	−0.04	−0.31, 0.22	0.74
Free T3	252	−0.02	−0.04, 0.00	153	−0.01	−0.04, 0.01	99	−0.02	−0.05, 0.02	0.85
2008 Thyroid Hormone Measurements
TSHd	235	11.89	−4.28, 30.32	146	14.66	−10.09, 46.21	89	2.71	−17.58, 28.00	0.17
Total T4	236	−0.09	−0.63, 0.45	146	0.16	−0.54, 0.87	90	−0.44	−1.28, 0.39	0.26
Free T4	237	0.01	−0.05, 0.06	146	0.02	−0.05, 0.09	91	−0.01	−0.10, 0.07	0.52
Free T3	237	0.01	−0.01, 0.02	146	0.01	−0.01, 0.03	91	0.00	−0.02, 0.02	0.84

Abbreviations: CI, confidence interval; T₃, triiodothyronine; T₄, thyroxine; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; TSH, thyroid-stimulating hormone.

^a Some participants were missing thyroid hormone measurements due to insufficient sample volume.

^b All models adjusted for age at thyroid hormone measurement and age at thyroid hormone measurement squared.

^c Coefficients represent the mean (free T₃, free T₄, and total T₄) or percent (TSH) change in thyroid hormone level for each 10-fold increase in serum TCDD concentration.

^d Percent change in serum TSH concentration was calculated using the following formula: (10^β − 1) × 100.