Endocrine Abstracts (2009) 20 P522

Iodine levels and thyroid hormones in healthy pregnant women and birth weight of their offspring

Mar Alvarez-Pedrerol1,2, Mònica Guxens1,2, Michelle Mendez1, Yolanda Canet3, Rosa Martorell4, Mercedes Espada5, Estel Plana1,2, Marisa Rebagliato2,6 & Jordi Sunyer1,7

1Centre for Research in Environmental Epidemiology, Barcelona, Spain; 2CIBER Epidemiologia y Salud Pública (CIBERESP), Barcelona, Spain; 3Hospital Parc Taulí, Sabadell, Spain; 4Hospital de Terrassa, Terrassa, Spain; 5Laboratorio Normativo de Salud Pública, Departamento de Sanidad Gobierno Vasco, Bilbao, Spain; 6Miguel Hernandez University, Valencia, Spain; 7Municipal Institute of Medical Research (IMIM-Hospital del Mar), Barcelona, Spain.

Introduction: The fetus is the most vulnerable to severe iodine deficiency and hypothyroidism during pregnancy. Severe iodine deficiency and hypothyroidism during pregnancy have long been known to be associated with neurologic deficits and mental retardation The effects of mild iodine deficiency and subclinical hypothyroidism are poorly known. The present study assesses the association between thyroid hormones and urinary iodine concentration (UIC) in healthy pregnant women and the birth weight of their children. The effect of iodine supplementation during pregnancy was also examined.

Methods: Six hundred and fifty-seven pregnant women were recruited in the city of Sabadell and followed until delivery. The association between thyroid hormones during the first trimester, UIC during the first and third trimesters and birth weight or small size for gestational age (SGA) was studied in 557 (85%), 251 (38%) and 528 (80%) mother–newborn pairs, respectively, using linear and logistic regression models adjusted for potential confounders. Six percent of newborns were classified as SGA.

Results: The median UIC was 95 and 104 μg/l during the first and third trimesters, respectively. Women with third trimester UICs between 100 and 149 μg/l had lower risk of having an SGA newborn than women with UICs below 50 μg/l (adjusted OR (95% CI): 0.15 (0.03–0.76)). There was no significant reduction in SGA among mothers with higher UICs. Lower free T4 and higher TSH levels during the first trimester were not associated with birth weight or SGA.

Conclusions: The present study suggests that iodine status during pregnancy may be related to prenatal growth. Further studies should be undertaken to assess the effects of moderate-to-mild iodine deficiency and iodine excess during pregnancy, as well as to validate the current guidelines in relation to reproductive and long-term outcomes in both iodine-deficient and iodine-sufficient areas.

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