Antenatal screening for thyroid dysfunction: pre-term birth, low birth-weight, and growth restriction

Figures & data

Figure 1. Flow diagram showing the derivation of cases and controls.

Table 1. Basic characteristics of cases and controls.

Characteristic	Cases	Controls	p Value^a
Singletons
Age (years)	31	30	<.0001
CRL (mm)	62.6	62.3	.07
Twins
Age (years)	32	34	.18
CRL (mm)	60.1	58.8	.42

^a Wilcoxon’s rank sum test, two-tail.

Table 2. Prevalence of pre-term birth, low birth-weight, and small for gestational age according to the thyroid screening test result.

Pregnancies with known outcome	Screening result		Risk ratio (95% CI)	p Value^a
	Positive	Negative
Singletons
Pre-term birth	11.0% (53/484)	6.5% (78/1203)	1.69 (1.21–2.36)	<.002
Low birth-weight	7.9% (37/470)	4.6% (45/983)	1.72 (1.13–2.62)	<.02
Term and low-birth-weight	2.3% (10/427)	1.3% (12/924)	1.80 (0.78–4.14)	.16
Small for gestational age	14.4% (67/466)	11.6% (105/905)	1.24 (0.93–1.65)	.14
Twins
Pre-term birth	82.6% (19/23)	80.0% (8/10)	1.03 (0.72–1.48)	.86
Low birth-weight^b	71.7% (33/46)	75.0% (15/20)	0.96 (0.70–1.31)	.78

^a Chi-square test.

^b Fetuses.

Table 3. Women with a positive thyroid screening test result: preterm birth and low birth-weight prevalence according to type of treatment.

Live-born infant with known outcome	Treatment		Risk ratio (95% CI)	p Value^a
	Thyroxine, propylthiouracil or surgery	None or iodine
Singletons
Pre-term birth	11.7% (23/196)	10.4% (30/288)	1.13 (0.68–1.88)	.65
Low birth-weight	10.0% (19/189)	6.4% (18/281)	1.57 (0.85–2.91)	.15
Term and low-birth-weight	3.5% (6/170)	1.6% (4/257)	2.27 (0.65–7.92)	.19
Small for gestational age	16.0% (30/187)	13.3% (37/279)	1.21 (0.78–1.80)	.40
Twins
Pre-term birth	80.0% (4/5)	83.3% (15/18)	0.96 (0.59–1.56)	.86
Low birth-weight^b	75.0% (9/12)	70.6% (24/34)	1.06 (0.72–1.57)	.77

^a Chi-square test.

^b Fetuses.

Table 4. Women with a positive thyroid screening test result: median antibody and hormone levels, and other factors, according to type of treatment.

Maternal/fetal factors	Treatment		p Value^a
	Thyroxine, propylthiouracil or surgery	None or iodine
Singletons
TPO (kU/l)	327 (197)^c	0.60 (280)	<.0001
TSH (mU/l)	3.54 (198)^c	0.27 (290)	<.0001
fT4 (pmol/l)	13.8 (136)^c	15.7 (191)	<.0001
Age (years)	31 (198)	31 (290)	.69
Weight (kg)	65 (198)^c	63 (290)	<.02
CRL (mm)	63.6 (198)	62.2 (290)	.19
Twins
TPO (kU/l)	212 (6)	0.20 (15)	<.001
TSH (mU/l)	3.34 (6)	0.16 (18)	<.0005
fT4 (pmol/l)	13.4 (5)	16.5 (16)	<.005
Age (years)	34 (6)	30 (18)	.30
Weight (kg)	72 (6)	68 (18)	.82
CRL (mm)^b	55.8 (12)	60.3 (35)	.29

^a Wilcoxon’s rank sum test, two-tail.

^b Fetuses.

^c Hypothyroid and hyperthyroid: TPO 338 and 83 (p < .05); TSH 3.67 and 0.01 (p < .0005); fT4 13.7 and 29.7 (p < .005); weight 65 and 56 (p < .02).

Table 5. Singleton cases: odds ratio, thyroxine, propylthiouracil or surgery compared with no treatment or iodine, adjusted for TPO, TSH, fT4 (when tested), and maternal weight.

Live-born infant with known outcome	Adjusted odds ratio (95% CI)	p Value^a
fT4 tested
Pre-term birth	1.08 (0.41–2.83)	.88
Low birth-weight	2.71 (0.93–7.90)	.07
Small for gestational age	1.93 (0.77–4.79)	.16
fT4 not tested
Pre-term birth	0.89 (0.19–4.19)	.88
Low birth-weight	0.05 (0.72–2.49)	.29
Small for gestational age	1.38 (0.26–7.31)	.70

^a Chi-square test.

Data availability statement

The data that support the findings of this study are available from the corresponding author, ID, upon reasonable request.