Maternal Thyroid Dysfunction and Risk of Seizure in the Child: A Danish Nationwide Cohort Study

Table 1

Characteristics of singletons born in Denmark between January 1, 1978, and November 30, 2006, and their mothers at birth of the child.

	No maternal thyroid dysfunction^a		Maternal hyperthyroidism^b				Maternal hypothyroidism^b
			Before birth		After birth		Before birth		After birth
	𝑛	%	𝑛	%	𝑛	%	𝑛	%	𝑛	%
Singletons	1,665,111	98.0	5,738	0.3	17,139	1.0	3,155	0.2	8,550	0.5
Maternal characteristics
Parity^c
Primipara	759,826	45.6	1,827	31.8	7,804	45.5	1,068	33.8	4,018	47.0
Multipara	905,285	54.4	3,911	68.2	9,335	54.5	2,087	66.2	4,532	53.0
Age (years)
<25	378,535	22.7	518	9.0	4,523	26.4	309	9.8	2,076	24.3
25–35	1,155,045	69.4	4,241	73.9	11,277	65.8	2,325	73.7	5,757	67.3
>35	131,531	7.9	979	17.1	1,339	7.8	521	16.5	717	8.4
Origin
Born in Denmark	1,520,213	91.3	5,090	88.7	15,556	90.8	2,698	85.5	7,497	87.7
Not born in Denmark	144,898	8.7	648	11.3	1,583	9.2	457	14.5	1,053	12.3
Residence^d
West Denmark	939,188	56.4	3,329	58.0	10,621	62.0	1,610	51.0	4,688	54.8
East Denmark	725,923	43.6	2,409	42.0	6,518	38.0	1,545	49.0	3,862	45.2
Child characteristics
Gender
Boy	854,831	51.3	2,884	50.3	8,665	50.6	1,615	51.2	4,429	51.8
Girl	810,280	48.7	2,854	49.7	8,474	49.4	1,540	48.8	4,121	48.2
Gestational age at birth (weeks)^e
<37	70,984	4.4	363	6.5	818	5.1	193	6.2	425	5.3
37–41	1,392,330	87.0	4,870	86.7	13,837	86.6	2,713	87.5	6,896	85.5
>41	138,383	8.6	382	6.8	1,328	8.3	196	6.3	740	9.2
Birth weight (grams)^e
Mean (SD)	3488 (559)		3442 (591)		3425 (567)		3546 (596)		3492 (584)
5 minutes Apgar score^f
7–10	1,635,867	99.2	5,625	99.0	16,854	99.3	3,096	99.1	8,415	99.4
0–6	12,554	0.8	55	1.0	118	0.7	27	0.9	49	0.6

aNo maternal diagnosis of hyper- or hypothyroidism registered in the Danish National Hospital Register (DNHR) before January 1, 2007.
^bMaternal first-time diagnosis of thyroid dysfunction (hyper- or hypothyroidism) before or after birth of the child and registered in DNHR before January 1, 2007.
^cNumber of births (live and stillbirths) including index pregnancy.
^dDivided into regions by the Great Belt: West Denmark with previously moderate iodine deficiency and East Denmark with previously mild iodine deficiency.
^eSingletons with missing value on gestational age or birth weight, registration of gestational age <20 or >45 weeks or birth weight <500 or >6000 grams not included (n = 65,235).
^fSingletons with missing value on 5-minute Apgar score not included (n = 17,033).