Low Birth Weight in Children Born to Mothers with Hyperthyroidism and High Birth Weight in Hypothyroidism, whereas Preterm Birth Is Common in Both Conditions: A Danish National Hospital Register Study.
OBJECTIVE
Maternal hyper- and hypothyroidism have been associated with increased risk of adverse pregnancy outcomes, but studies have led to inconsistent results. We aimed to identify children born to mothers with a hospital-recorded diagnosis of thyroid dysfunction in Denmark and to study the association with gestational age at delivery and birth weight of the child.


METHODS
Population-based cohort study using Danish nationwide registers. All singleton live births in Denmark between January 1, 1978 and December 31, 2006 were identified and stratified by maternal diagnosis of hyper- or hypothyroidism registered in the Danish National Hospital Register before January 1, 2007.


RESULTS
Maternal first-time diagnosis of thyroid dysfunction before, during or after pregnancy was registered in 32,809 (2.0%) of the singleton live births (n = 1,638,338). Maternal diagnosis of hyperthyroidism (adjusted OR 1.22, 95% CI 1.15-1.30) and hypothyroidism (adjusted OR 1.17, 95% CI 1.08-1.27) were associated with increased risk of preterm birth. Moreover, birth weight in children born to mothers with a diagnosis of hyperthyroidism was lower (adjusted difference -51 g, 95% CI -58 to -43 g) and higher in relation to maternal hypothyroidism (adjusted difference 20 g, 95% CI 10-30 g). Hyperthyroidism was associated with small-for-gestational-age (adjusted OR 1.15, 95% CI 1.10-1.20) and hypothyroidism with large-for-gestational-age children (adjusted OR 1.24, 95% CI 1.17-1.31).


CONCLUSIONS
Based on Danish nationwide registers, both maternal hyper- and hypothyroidism were associated with increased risk of preterm birth. Actual birth weight of the child and birth weight for gestational age were low if the mother had a diagnosis of hyperthyroidism and high if the diagnosis was hypothyroidism.
Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark.
Stine Linding
SL
Andersen
Section for Epidemiology, Department of Public Health, Aarhus University, Aarhus, Denmark.
Jørn
J
Olsen
Section for Epidemiology, Department of Public Health, Aarhus University, Aarhus, Denmark.
Chun Sen
CS
Wu
Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark.
Peter
P
Laurberg
Birth length; Birth weight; Danish National Hospital Register; Gestational age; Hyperthyroidism; Hypothyroidism; Iodine; Pregnancy; Thyroid disease