Table 1.

Maternal thyroid hormone levels during the first 16 weeks of pregnancy

Hormone	n = 381	(%)	Mean ± SDa	P10c	P50c	P90c
Free T4(ng/dL) b			0.79 ± 0.34	0.48	0.75	0.96
< 0.76	207	54.3
≥ 0.76	174	45.7
TSH (mUI/L) b			1.24 ± 1.30	0.22	0.87	2.58
≤ 4	371	97.4
> 4	10	2.6
Overt hypothyroidismd	7	1.8
Sub-Clinical hypothyroidismd	3	0.8
Isolated Hypothyroxinemiad	197	51.71
Without Hypothyroxinemiae	174	45.67

^aArithmetic mean and Standard Deviation (SD)

^bGeometric mean and SD: TSH = 0.83 ± 0.8 mUI/L; Free T4 = 0.75 ± 0.3 ng/dL

^c10, 50 and 90 percentiles

^dHypothyroxinemia includes: Overt hypothyroidism (TSH concentrations > 4 mlU/L and a free T4 concentration < 0.76 ng/dL); Subclinical hypothyroidism (TSH concentrations >4mlU/L, and a free T4 concentration ≥ 0.76 ng/dL); Isolated hypothyroxinemia (TSH concentrations ≤4 mlU/L and a free T4 concentration < 0.76 ng/dL)

^eWithout hypothyroxinemia: a free T4 concentration ≥ 0.76 ng/dL)