Table 1 Comparison of the maternal and child characteristics among the 3 groups

Maternal age (years)

29.4(27.1–32.2)

29.6(27–32.8)

30(27.1–31.9)

0.833

Maternal education levels

0.116

 Low (high school and below)

2200(15.4)

46(18.5)

5(6.6)

 Middle (vocational college)

6166(43.2)

109(44)

34(44.7)

 High (university and above)

5919(41.4)

93(37.5)

37(48.7)

Current employment status

0.045

 Yes

12,590(88.1)

219(88.3)

74(97.4)

 No

1695(11.9)

29(11.7)

2(2.6)

Parity

0.002

 Primipara

8029(56.2)

161(64.9) ^a

52(68.4)

 Multipara

6256(43.8)

87(35.1) ^a

24(31.6)

Pre-pregnancy BMI

0.725

 Underweight

1371(9.6)

21(8.5)

5(6.6)

 Normal weight

9303(65.1)

157(63.3)

47(61.8)

 Overweight

2821(19.7)

54(21.8)

18(23.7)

 Obesity

790(5.5)

16(6.5)

6(7.9)

 Gestational age at thyroid function testing (weeks)

8.9(8–10.1)

8.8(8–10.6)

8.7(7.9–10.5)

0.828

 TSH (mIU/L)

0.90(0.51–1.34)

2.67(2.56–2.77) ^a

2.71(2.61–2.81) ^b

 < 0.001

 FT4 (pmol/L)

13.64(12.67–14.77)

12.93(12.09–13.74) ^a

12.94(11.88–13.78) ^b

 < 0.001

 Gestational age at delivery (weeks)

39.6(38.9–40.4)

39.9(39.1–40.7)

39.9(39–40.6)

0.058

Gender

0.073

 Girls

6951(48.7)

106(42.7)

31(40.8)

 Boys

7334(51.3)

142(57.3)

45(59.2)

 Birth weight (g)

3370(3100–3660)

3365(3107.5–3680)

3395(3095–3622.5)

0.992