	Pregnant women (1st) (n=438)	Non-pregnant women (n=156)	P-Value
Age (old-years)	25.4±5.1	24.9±6.7	0.458
BMI	24.9±4.1	20.9±3.8	----
Gestational Age	9.0±2.0	----	-----
Iodinated Salt	20±5	20±4	NS
TSH (mIU/L) (Medina – Min - Max)	0.80 0.05 – 14.0	1.7 0.3 – 5.5	0.001
Age<25 years	0.9 (0.05 – 7.0)	1.8 (0.3 – 5.5)	-----
Age 25 – 29.99 years	1.0 (0.05 – 3.8)	1.4 (0.6 – 4.3)	----
Age 30 – 34.99 years	0.70 (0.05 – 9.2)	1.25 (0.5 – 3.2)	---
Age >35 years	0.75 (0.05 – 14.0)	1.25 (0.3 – 2.9)	----
5th percentile of TSH	0.05	0.6	----
50th percentile of TSH	0.85	1.6
95th percentile of TSH	2.8	3.95	----
FT4 (pmol/L) (Medina – Min - Max)	14.6 5.2 – 46.3	13.5 9.1 – 23.1	0.009
5th percentile of FT4	9.1	9.1	----
50th percentile of FT4	14.2	14.5
95th percentile of FT4	21.9	19.5	-----
UIE (µg/L) (Median, Min – Max)	74 1 - 286	144 4 – 440	0.001
Urine Cr (mg/dL) (Median, Min – Max)	1.47 0.12 – 5.1	1.34 (0.15 – 3.9)	0.01
UIC/Cr ratio (µg/mg) (Median, Min – Max)	47 1 – 870	134 2 – 600	0.001
TPO-Ab (IU/L) (Median, Min – Max)	2.6 0.5 – 316	3.3 0.1 – 538	0.03

Table 1: Biochemical parameters of thyroid function during gestation in healthy iodine mild to moderate

Variable

Pregnant women
(n=438)

Non-Pregnant women
(n=156)

Iodine deficient
(UIE < 150µg/L)
(n=380 ;87%)

Iodine sufficient
(UIE > 150µg/L)
(n= 58; 13%)

Iodine deficient
(UIE < 100µg/L)
(n=27; 18%)

Iodine sufficient
(UIE > 100µg/L)
(n=129; 82%)

TSH*

Median
Min-Max

0.9
0.05 – 14.0

0.8
0.05 – 3.8

1.90
0.4 – 5.5

1.7
0.3 – 5.5

P5 – P95

0.05 – 2.8

0.1 – 3.3

0.49 – 5.1

0.6 – 4.1

fT4*

Median
Min-Max

14.2
5.2 – 46.6

14.1
5.5 – 28.3

12.9
9.1 – 23.9

14.2
9.1 – 23.1

P5 – P95

9.0 – 21.9

9.1 – 21.9

10.1 – 22.1

9.1 – 19.4

Table 2: Median and 5th and 95th percentiles of thyroid function test values for participants with and without iodine deficiency in 2 groups.

variable

Pregnant women
(n=490)

Non-pregnant women
(n=181)

TPO +
(n= 52)

TPO ‒
(n= 438)

P-value

TPO +
(n=25)

TPO ‒
(n=156)

P-value

TSH*
(mIU/L)

Median
Min-Max

1.6
0.05 – 9.2

0.8
0.05 – 14.0

0.001

2.1
(0.7 – 5.5)

1.7
(0.30 – 4.87)

0.05

P5 – P95

0.2 – 4.2

0.05 – 2.8

0.03

0.75 – 5.5

0.6 – 3.95

-----

fT4*
(pmol/L)

Median
Min-Max

11.6
6.5 – 25.7

14.1
5.2 – 46.3

0.03

14.1
9.1 – 23.1

12.9
9.1 – 23.1

0.150

P5 – P95

7.7 – 25.1

9.1 – 21.9

-----

9.1 – 23.1

9.1 – 19.3

-----

Table 3: Median and 5th and 95th percentiles of thyroid function test values for participants with positive and negative thyroid peroxidase antibody (TPO-Ab) in both groups of pregnant and non-pregnant women.

Study

Country

Sample size and
Design

Centiles’ used

TSH reference intervals

1st trimester

Non-pregnant women

Preset study 2019

Iran

Cohort
n=645

P5 – p95

0.05 – 2.8

0.6 – 3.95

Azizi F 2012
(10)

Iran

Cohort
n=261

P5 – p95

0.20 – 3.90

-----

Delshad 2021
(

Mehran L 2013
(11)

Iran

Cohort
n=215

P5 – p95

0.20 – 3.90

-----

Karakosta 2011
(22)

Greece

Cohort
n=425

P2.5 – P97.5

0.05 – 2.53

------

Nazarpour S2018
(12)

Iran

Cohort
n=425

P2.5 – P97.5

0.14 - 6.14

------

Kianpour et al. 2019
(14)

Iran

cross sectional
n= 880

P2.5 – P97.5

0.20–4.60

0.59–5.60

Zhang D et al. 2019
(27)

China

Cohort
n=805

P5 – P95

0.02 – 3.78

-----

Kim H et al. 2018
(29)

S. Korea

Cohort
n=459

P5 – P95

0.03 – 4.24

------

Kostecka-Matyja, M2017 (24)

Poland

Cohort
n=172

P5 – P95

0.009-3.177

------

Khalil A et al. 2018
(30)

UEA

Cohort
n=414

P5 –P95

0.094 – 3.33

------

Ollero MD
2019 (32)

Spain

Longitudinal
n=400

P5 – P95

0.13 – 4.16

-------

Goel et al 2021
(40)

India

Cross-sectional
n=604

P5 – P95

0.59 –4.48

------

Castillo C et al.2018
(28)

Chile

Cross-sectional
n=670

P2.5 – P97.5

0.13 – 5.37

-----

Table 4: comparison local reference range for TSH with national and international studies reporting trimester-specific reference intervals for TSH during pregnancy