. 2015 Oct 20;124(6):861–867. doi: 10.1289/ehp.1409614

Table 2.

Maternal thyroid hormone concentrations stratified by various demographic factors.

Category	n (%)	T4 (μg/dL)			fT4 (ng/dL)			TSH (μIU/mL)^a
Category	n (%)	Median	Mean ± SD	p-Value^b	Median	Mean ± SD	p-Value^b	Median	Mean ± SD	p-Value^b
Mother’s age (years)
< 21	435 (23.1)	12.43	12.50 ± 1.87		0.87	0.87 ± 0.14		1.26	1.36 ± 0.77
21–25	563 (29.9)	12.36	12.45 ± 1.91		0.86	0.87 ± 0.23		1.16	1.35 ± 0.88
26–30	414 (22.0)	12.26	12.38 ± 1.88		0.84	0.85 ± 0.24		1.16	1.36 ± 0.98
> 30	468 (24.9)	11.91	11.90 ± 1.83		0.83	0.83 ± 0.13		1.23	1.38 ± 0.80
R			–0.12	< 0.001		–0.14	< 0.001		0.01	0.78
Mother’s education (highest grade)
< 9	509 (27.6)	12.42	12.57 ± 1.96		0.84	0.86 ± 0.30		1.12	1.33 ± 0.90
9–11	308 (16.7)	12.31	12.35 ± 2.08		0.85	0.86 ± 0.15		1.22	1.41 ± 0.87
12	568 (30.8)	12.23	12.22 ± 1.81		0.85	0.86 ± 0.13		1.21	1.32 ± 0.82
> 12	460 (24.9)	12.05	12.07 ± 1.73		0.85	0.85 ± 0.12		1.26	1.44 ± 0.86
R			–0.10	< 0.001		0.02	0.31		0.07	0.003
Mother’s weight (lbs)
< 121	469 (24.9)	12.38	12.49 ± 1.77		0.87	0.89 ± 0.25		1.15	1.32 ± 0.85
122–145	471 (25.1)	12.10	12.09 ± 1.80		0.85	0.86 ± 0.12		1.17	1.31 ± 0.82
146–171	466 (24.8)	12.31	12.39 ± 1.81		0.85	0.86 ± 0.23		1.23	1.38 ± 0.87
> 171	474 (25.2)	12.25	12.27 ± 2.13		0.83	0.83 ± 0.14		1.27	1.44 ± 0.90
R			–0.01	0.54		–0.14	< 0.001		0.06	0.01
Serum collection (weeks gestation)
< 16	467 (24.8)	12.48	12.56 ± 1.75		0.88	0.89 ± 0.14		1.15	1.29 ± 0.86
17	512 (27.2)	12.20	12.32 ± 1.84		0.85	0.86 ± 0.21		1.25	1.37 ± 0.77
18	448 (23.8)	12.15	12.16 ± 1.82		0.82	0.84 ± 0.12		1.16	1.36 ± 0.87
> 18	453 (24.1)	12.25	12.19 ± 2.11		0.83	0.84 ± 0.25		1.24	1.43 ± 0.94
R			–0.07	0.004		–0.19	< 0.001		0.04	0.08
TG (IU/mL)
≤ 4	1,719 (91.4)	12.22	12.25 ± 1.83		0.85	0.86 ± 0.20		1.20	1.36 ± 0.82
> 4	161 (8.6)	12.97	12.97 ± 2.30	< 0.001	0.83	0.84 ± 0.13	0.05	1.17	1.43 ± 1.25	0.16
TPO (IU/mL)
≤ 9	1,715 (91.2)	12.26	12.33 ± 1.87		0.85	0.86 ± 0.20		1.16	1.28 ± 0.71
> 9	165 (8.8)	12.23	12.10 ± 2.07	0.47	0.82	0.82 ± 0.13	0.006	1.65	2.21 ± 1.54	< 0.001
Ethnicity
Hispanic	1,303 (69.3)	12.38	12.47 ± 1.90	Ref	0.85	0.86 ± 0.21	Ref	1.17	1.34 ± 0.86	Ref
White	391 (20.8)	11.88	11.87 ± 1.72	< 0.001	0.84	0.84 ± 0.12	0.17	1.31	1.52 ± 0.91	< 0.001
Asian	72 (3.8)	12.30	12.17 ± 2.27	0.54	0.84	0.83 ± 0.14	0.48	1.20	1.23 ± 0.66	0.53
Black	24 (1.3)	11.92	11.37 ± 1.84	0.01	0.90	0.90 ± 0.13	0.10	1.19	1.44 ± 0.83	0.55
Other	90 (4.8)	12.01	12.32 ± 1.74	0.16	0.87	0.90 ± 0.19	0.06	0.94	1.04 ± 0.69	< 0.001
Mother’s birthplace
USA	854 (45.4)	12.10	12.16 ± 1.81	Ref	0.85	0.85 ± 0.13	Ref	1.25	1.42 ± 0.86	Ref
Mexico	889 (47.3)	12.38	12.45 ± 1.97	0.001	0.84	0.86 ± 0.24	0.65	1.16	1.32 ± 0.87	0.002
Other	137 (7.3)	12.28	12.35 ± 1.79	0.20	0.88	0.90 ± 0.14	< 0.001	1.13	1.24 ± 0.73	0.02
Abbreviations: fT4, free thyroxine; R, Spearman correlation coefficient; Ref, reference category; T4, total thyroxine; TG, thyroglobulin antibody; TPO, thyroperoxidase antibody; TSH, thyroid stimulating hormone. ^aOne subject was missing a serum TSH value. ^bWhen the variables are continuous, p-values are provided for the Spearman correlation coefficient between the two continuous variables. When variables are ordinal, p-values are provided comparing the mean thyroid hormone value in each group to a reference group.