Association between Maternal Thyroxine and Risk of Fetal Congenital Heart Defects: A Hospital-Based Cohort Study

Table 1

Basic characteristics of the population.

Characteristics	Congenital heart defects		values^a
	No (N = 41,432)	Yes (N = 215)
FT4 (pmol/L, median, IQR)	14.7 (13.2–16.4)	15.6 (13.8–17.1)	<0.001
TT4 (ng/ml, median, IQR)^b	11.1 (9.8–12.4)	11.1 (9.9–12.4)	0.92
FTT4P (%, median, IQR)^b,c	1.05 (0.95–1.17)	1.09 (0.99–1.20)	0.004
Antibody positivity^b (n, %)	4,885 (13.9)	30 (15.7)	0.20
Maternal age (years; n, %)
<25	2,100 (5.1)	10 (4.7)	0.31
25–34	35,231 (85.0)	177 (82.3)
≥35	4,101 (9.9)	28 (13.0)
Local residents (n, %)	31,866 (76.9)	164 (76.3)	0.83
Nulliparous women (n, %)	35,153 (84.8)	188 (87.4)	0.29
Assisted conceptions (n, %)	747 (1.8)	6 (2.8)	0.28
Gestational diabetes (n, %)	3,478 (8.4)	23 (10.7)	0.23
Preeclampsia (n, %)	2,337 (5.6)	31 (14.4)	<0.001
Male fetuses (n, %)	21,345 (51.5)	118 (45.8)	0.33

Abbreviations: IQR, interquartile range; FT4, free thyroxine; TT4, total thyroxine; and FTT4P, free-to-total thyroxine proportion. ^a values for Mann–Whitney U tests or chi-square/Fisher’s exact tests. ^bA total of 39,077 women (38,984 women with a non-CHD baby and 93 women with a CHD offspring) had measured TT4 and an FTT4 value. 35,339 women had tested thyroid antibody, including 35,256 women without a CHD baby. ^cMolecular weight of 776.87 g/mol for thyroxine was used for the transformation.