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

Table 2

Hazard ratio (HR) with 95% confidence interval (95% CI) for seizure in singletons born in Denmark, 1978–2006, according to maternal diagnosis of hyper- or hypothyroidism registered in the Danish National Hospital Register (DNHR) before January 1, 2007. Reference is singletons born to mothers with no diagnosis of thyroid dysfunction registered in DNHR before January 1, 2007.

	Singletons (n)	Crude HR (95% CI)	Adjusted HR (95% CI)^a	P ^b
Seizure^c
No hyper- or hypothyroidism	77,444	1.00 (reference)	1.00 (reference)
Hyper- or hypothyroidism	1,844	1.11 (1.06–1.16)	1.12 (1.07–1.18)	<0.001
Hyperthyroidism	1,185	1.06 (1.00–1.12)	1.08 (1.02–1.15)	0.009
Hypothyroidism	659	1.20 (1.11–1.30)	1.20 (1.11–1.30)	<0.001
Neonatal seizure^d
No hyper- or hypothyroidism	3,109	1.00 (reference)	1.00 (reference)
Hyper- or hypothyroidism	89	1.39 (1.13–1.71)	1.42 (1.15–1.75)	0.001
Hyperthyroidism	50	1.18 (0.89–1.56)	1.22 (0.92–1.62)	0.161
Hypothyroidism	39	1.80 (1.31–2.47)	1.78 (1.30–2.44)	<0.001
Febrile seizure^e
No hyper- or hypothyroidism	55,798	1.00 (reference)	1.00 (reference)
Hyper- or hypothyroidism	1,249	1.08 (1.02–1.14)	1.09 (1.03–1.15)	0.003
Hyperthyroidism	779	1.02 (0.95–1.09)	1.03 (0.95–1.11)	0.464
Hypothyroidism	470	1.20 (1.10–1.32)	1.21 (1.10–1.32)	<0.001
Epilepsy^f
No hyper- or hypothyroidism	22,173	1.00 (reference)	1.00 (reference)
Hyper- or hypothyroidism	628	1.25 (1.15–1.35)	1.21 (1.11–1.31)	<0.001
Hyperthyroidism	426	1.24 (1.13–1.37)	1.20 (1.09–1.32)	<0.001
Hypothyroidism	202	1.26 (1.09–1.44)	1.22 (1.06–1.40)	0.005

aAdjusted model included gender of the child (boy/girl), birth year (<1980, 1980–1982, 1983–1985, 1986–1988, 1989–1991, 1992–1994, 1995–1997, 1998–2000, 2001–2003, 2004–2006), and the following maternal variables obtained at the time of the child’s birth: age (<20, 20–24, 25–29, 30–34, 35–39, ≥40 years), parity including index pregnancy (1, 2, 3, ≥4), cohabitation (married/not married), income (1st, 2nd, 3rd, 4th quartile), origin (born in Denmark/not born in Denmark), residence (East/West Denmark), and maternal diagnosis of febrile seizure and/or epilepsy registered in the Danish National Hospital Register (DNHR) before January 1, 2007 (yes/no).
^bP value for results of the adjusted model.
^cDiagnosis of neonatal seizure, febrile seizure, and/or epilepsy.
^dDiagnosis of seizure in the neonatal period (first 28 days of life).
^eDiagnosis of febrile seizure after the neonatal period and before the age of 5 years with no previous diagnosis of epilepsy or neonatal seizure.
^fDiagnosis of epilepsy after the neonatal period and before January 1, 2007. Epilepsy diagnosis following neonatal seizure (n = 654), following febrile seizure (n = 3,104).