Table IV.

Reference intervals of thyroid function in normal pregnant women.

		FT3 (2.5–3.9 ng/l)		FT4 (0.58–1.64 ng/dl)		TSH (0.34–5.6 uIU/ml)
Gestational weeks	n	M (P2.5-P97.5)	IQR	M (P2.5-P97.5)	IQR	M (P2.5-P97.5)	IQR
8–14	849	2.90 (2.33–3.65)	0.45	0.81 (0.59–1.11)	0.16	1.28 (0.17–4.59)	1.22
15–20	1,655	2.72(2.30–3.45)	0.45	0.70 (0.58–0.91)	0.11	1.68 (0.32–4.68)	1.1
21–36	1,247	2.62 (2.07–3.24)	0.38	0.60 (0.44–0.80)	0.12	1.88 (0.56–4.95)	1.24
≥37	1,152	2.26 (1.73–2.84)	0.39	0.61 (0.44–0.82)	0.14	2.3 (0.53–5.10)	1.67
Total	4,903	2.63 (1.90–3.43)	0.52	0.68 (0.46–0.97)	0.16	1.78 (0.31–5.06)	1.37

In pregnant women, the median of FT3, FT4 and TSH levels demonstrated an overall increased trend from the 8–14 to ≥37 gestational week groups, except for the FT4 levels in the 21–36 group, which was lower than that of ≥37 weeks. Data are presented as mean ± standard deviation. M, median; IQR, interquartile range; FT3, free triiodothyronine; FT4, free thyroxine; TSH, thyroid stimulating hormone.