Maternal thyroid disorder in pregnancy and risk of cerebral palsy in the child: a population-based cohort study

BMC Pediatrics

Table 3 Assessment of misclassification of exposure to maternal thyroid disorder

Agreement between sources of maternal thyroid disorder in 90,088 danish children included in both the danish register-based study population and MOBAND study population
Register-based information ^a	Self-report
Register-based information ^a	Unexposed	Hypothyroidism	Hyperthyroidism	Unclassifiable	Total
Unexposed	88,841	110	48	158	89,157
Hypothyroidism	164	240	17	68	489
Hyperthyroidism	213	21	147	21	402
Unclassifiable	19	14	4	3	40
Total	89,237	385	216	250	90,088
	Observed proportionate agreement
Proportion of positive agreement	0.60
Proportion of negative agreement	0.99
Kappa	0.60, p < 0.001
Bias-adjusted estimates of thyroid disorder and risk of cerebral palsy
	All CP	Unilateral spastic CP	Bilateral spastic CP
Bias-adjusted OR^b (study error)^c in register-based study population	0.89 (0.40–1.21)	1.20 (0.72–3.83)	0.77 (0.24–1.22)

Abbreviations: CP cerebral palsy, OR odds ratio
^aThe exposure window of the register-based measure was changed to an identified thyroid disorder before pregnancy until week 18 of gestation in order to correspond with the measure based on maternal self-report in MOBAND
^bRaw estimates adjusted for misclassification using a probabilistic approach assuming non-differential misclassification of exposure. Assumptions regarding level of sensitivity and specificity were guided by the calculated positive and negative agreement (for more details see Additional file 1: eMethod 3)
^cStudy error includes both systematic error (interval encompassing 95% of the corrected estimates) and random error (95% confidence interval)

ISSN: 1471-2431