Abstract
INTRODUCTION: Overt hypothyroidism in pregnancy is associated with adverse outcomes, but the effects of subclinical hypothyroidism and isolated hypothyroxinemia on pregnancy outcomes are still controversial. Subclinical hypothyroidism might be associated with preterm delivery, low Apgar score, fetal death and miscarriages and isolated hypothyroxinemia with preterm labor, high birth weight and neurocognitive deficits in children. Other studies show no association with any complications at all. In the present study we tried to estimate whether maternal subclinical hypothyroidism and isolated hypothyroxinemia are associated with complications during pregnancy in our population which represents the pregnant population of Western Greece. METHODS: In a total of 469 pregnant women, third trimester serum was assayed for thyroid-stimulating hormone (TSH) and free thyroxine (free T4). Thyroid hypofunction was defined as 1) subclinical hypothyroidism with TSH levels above 3 mIU/L for the 3rd trimester and normal free T4 and 2) isolated hypothyroxinemia with TSH levels below 3 mIU/L for the 3rd trimester and free T4 below the 5th percentile. The results were associated with birth weight, week of labor, history of miscarriages and demographic characteristics. Patients with thyroid hypofunction were compared with euthyroid patients (TSH and free T4 between normal limits). The results were analyzed with one-way ANOVA and χ2 test. RESULTS: Subclinical hypothyroidism was documented in 10.9% and isolated hypothyroxinemia in 21.7% of pregnant women. Subclinical hypothyroidism was not associated with birth weight, week of labor, or history of miscarriages. On the contrary, hypothyroxinemia was associated with high birth weight (P < 0.05). CONCLUSION: In our study, we did not find a link between subclinical hypothyroidism and adverse pregnancy outcomes. Similarly, hypothyroxinemia was not associated with pregnancy complications. However, it was associated with higher birth weight. Our studies contribute to our understanding, whether or not subclinical hypothyroidism and isolated hypothyroxinemia are associated with pregnancy adverse outcomes and whether treatment and test for hypothyroidism should become routine during pregnancy.
Highlights
Overt hypothyroidism in pregnancy is associated with adverse outcomes, but the effects of subclinical hypothyroidism and isolated hypothyroxinemia on pregnancy outcomes are still controversial
In the present study we tried to estimate whether maternal subclinical hypothyroidism and isolated hypothyroxinemia are associated with complications during pregnancy in our population which represents the pregnant population of Western Greece
Maternal thyroid hypofunction was defined as 1) subclinical hypothyroidism when TSH was more than 3 mIU/L for the 3rd trimester and free T4 between the 5th and 95th percentiles or 2) isolated hypothyroxinemia when TSH was less than 3 mIU/L for the 3rd trimester and free T4 less than the 5th percentile
Summary
Normal pregnancy entails substantial changes in maternal thyroid function Inadequate adaptation to these changes in thyroid physiology results in thyroid dysfunction [1] [2]. It is established that overt hypothyroidism in pregnancy is associated with many of adverse outcomes, the effects of subclinical hypothyroidism and isolated hypothyroxinemia on pregnancy outcomes are still controversial [9]-[18]. Subclinical hypothyroidism affects 0.4% - 1% of pregnancies and isolated hypothyroxinemia about 2%, in iodinesufficient regions and 25% - 30% in iodine deficient regions [24].
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