TABLE 1.

Demographic characteristics of pregnant women and their offspring according to serum concentrations of thyroid hormones, Salinas Valley, California, 1999–2000

	No. of subjects†	%†	Thyroid hormone
			Free thyroxine (mean) (ng/dl)	Total thyroxine (mean) (μg/dl)	Thyroid-stimulating hormone (geometric mean) (mIU/liter)
Child
Sex
Male	164	49	0.83 (0.25)‡	10.6 (1.5)‡	1.14 (1.81)§
Female	170	51	0.82 (0.23)	10.6 (1.6)	1.19 (1.66)
Birth weight (g)
<2,500	12	4	0.79 (0.22)*	10.6 (1.8)	1.34 (1.37)
2,500–3,500	174	52	0.86 (0.25)	10.8 (1.5)	1.17 (1.84)
>3,500	148	44	0.79 (0.23)	10.5 (1.6)	1.14 (1.63)
Gestational age (weeks) at birth
<37	24	7	0.71 (0.21)**	10.4 (1.5)	1.21 (1.67)
37–42	310	93	0.83 (0.24)	10.7 (1.6)	1.16 (1.74)
>42	0	0
Mother
Age (years)
18–24	158	47	0.87 (0.25)***	10.8 (1.6)**	1.09 (1.80)*
25–29	108	32	0.81 (0.22)	10.7 (1.6)	1.30 (1.69)
30–34	45	13	0.74 (0.22)	10.4 (1.1)	1.16 (1.59)
35–45	23	7	0.71 (0.21)	9.6 (1.5)	1.07 (1.68)
Race/ethnicity
White	7	2	0.77 (0.21)	10.9 (2.3)	1.05 (1.50)
Latino	320	96	0.83 (0.24)	10.6 (1.6)	1.17 (1.74)
Other	7	2	0.89 (0.23)	11.4 (1.5)	0.91 (1.53)
Education
≤6th grade	140	42	0.85 (0.24)	10.4 (1.5)	1.13 (1.90)
7th–12th grade (no diploma)	118	35	0.80 (0.25)	10.7 (1.7)	1.21 (1.63)
High school diploma or more	76	23	0.83 (0.22)	10.9 (1.5)	1.13 (1.57)
Family income
Poverty line or less	188	60	0.82 (0.22)	10.7 (1.6)	1.11 (1.79)
Above poverty line–200% of poverty line	111	36	0.81 (0.24)	10.7 (1.5)	1.25 (1.63)
>200% of poverty line	12	4	0.91 (0.43)	9.8 (1.4)	1.30 (1.60)
Country of birth
United States	41	12	0.86 (0.28)	11.2 (1.6)**	1.12 (1.59)**
Mexico	286	86	0.82 (0.24)	10.5 (1.6)	1.19 (1.71)
Other	7	2	0.80 (0.13)	11.1 (1.0)	0.55 (2.99)
Parity
0	109	33	0.86 (0.26)	10.6 (1.6)	1.21 (1.57)
≥1	225	67	0.81 (0.23)	10.6 (1.6)	1.14 (1.81)
Time (years) in the United States
≤5	182	54	0.84 (0.26)	10.6 (1.5)	1.22 (1.86)
6–10	78	23	0.80 (0.19)	10.4 (1.7)	1.07 (1.62)
≥11	74	22	0.82 (0.25)	10.9 (1.6)	1.11 (1.52)
Smoking during pregnancy
Yes	22	7	0.79 (0.21)	10.9 (1.6)	1.15 (1.50)
No	312	93	0.83 (0.24)	10.6 (1.6)	1.16 (1.75)
Alcohol drinking during pregnancy
Yes	76	23	0.79 (0.21)	10.5 (1.6)	1.20 (1.55)
No	254	77	0.83 (0.25)	10.7 (1.6)	1.15 (1.79)
Prepregnancy body mass index¶
<25	127	39	0.86 (0.24)	10.6 (1.4)	1.09 (1.90)
25–30	131	41	0.82 (0.22)	10.7 (1.6)	1.24 (1.64)
>30	65	20	0.79 (0.23)	10.6 (1.8)	1.16 (1.64)

* p < 0.10; **p < 0.05; ***p < 0.001 (two-sided p value calculated using analysis of variance).

^†Numbers do not always add to the total number of participants because of missing values. Percentages may not add to 100% because of rounding.

^‡Numbers in parentheses, standard deviation.

^§Numbers in parentheses, geometric standard deviation.

^¶Weight (kg)/height (m)².