First- and Second-Trimester Reference Intervals for Thyroid Hormones during Pregnancy in “Rhea” Mother-Child Cohort, Crete, Greece

Table 2

Thyroid hormones according to gestational age, Rhea mother-child cohort, Crete, Greece.

	𝑁	Distribution	2.5th percentiles	97.5th percentile	Median	Mean	SD	Reference range
1st trimester
TSH^a 𝜇IU/mL	141	Not normal	0.05	2.53	1.02	1.08	0.61	0.05–2.53
free T3^b  pg/mL (pmol/L)	141	Normal^d	1.84 (2.83)	5.39 (8.28)	3.21 (4.93)	3.38 (5.19)	0.94 (1.44)	1.54–5.22 (2.37–8.02)
free T4^c  ng/dL (pmol/L)	139	Normal^e	0.96 (12.36)	1.60 (20.59)	1.24 (15.96)	1.24 (15.96)	0.15 (1.93)	0.95–1.53 (12.23–19.69)
2nd trimester
TSH^a 𝜇IU/mL	257	Not normal	0.18	2.73	1.14	1.23	0.65	0.18–2.73
free T3^b pg/mL (pmol/L)	256	Normal	1.99 (3.06)	5.30 (8.14)	3.52 (5.41)	3.55 (5.45)	0.87 (1.34)	1.78–5.29 (2.73–8.13)
free T4^c ng/dL (pmol/L)	258	Normal	0.84 (10.81)	1.44 (18.53)	1.16 (14.93)	1.16 (14.93)	0.15 (1.93)	0.87–1.45 (11.20–18.66)

TSH: thyroid-stimulating hormone; free T3: free triiodothyronine; free T4: free thyroxine.
^aDifference between first and second trimester: 𝑃=0.058.
^bDifference between first and second trimester: 𝑃=0.054.
^cDifference between first and second trimester: 𝑃<0.001.
^dAfter outlier deletion and log transformation.
^eAfter outlier deletion.