Prevalence of Thyroid Dysfunction in Women in Early Pregnancy

Does It Increase With Maternal Age?

Marta Diéguez; Ana Herrero; Noelia Avello; Patricio Suárez; Elías Delgado; Edelmiro Menéndez¶,**


Clin Endocrinol. 2016;84(1):121-126. 

In This Article

Abstract and Introduction


Objective Recent studies report high rates of thyroid disorders in pregnant women. However, the need for universal thyroid screening remains controversial. Our aim was to estimate the prevalence of thyroid dysfunction (TD) during pregnancy and to analyse the association with maternal age.

Design and methods We conducted a cross-sectional study in a referral centre in collaboration with the primary care units from April 2010 to March 2011. The study included 2509 consecutive pregnant women resident in an iodine-sufficient area, mean age 32 years (range 16–47) who were universally screened for TD in their first trimester (median gestation 8 weeks, range 4–13 weeks). Thyroid-stimulating hormone (TSH) and free T4 (FT4) were analysed during the first antenatal visit. We applied first trimester-specific population-based TSH and FT4 reference ranges.

Results We identified 416 women with positive TD screening [16·6%, 95% confidence interval (95% CI) 15·1–18·0]. Of these, 47 had overt hypothyroidism (1·9%), 90 subclinical hypothyroidism (3·6%), 23 overt hyperthyroidism (0·9%), 20 subclinical hyperthyroidism (0·8%) and 236 had isolated hypothyroxinaemia (9·4%). Applying a logistic regression model, age ≥30 years was not associated with a higher risk of TD [odds ratio (OR) 0·85, 95% CI 0·67–1·08] or hypothyroidism (OR 0·72, 95% CI 0·50–1·06).

Conclusions TD affects one in six pregnant women in an iodine-sufficient population. Maternal age ≥30 years do not increase the risk of TD.


Thyroid disease commonly affects women of childbearing age and is the second most common endocrinological disorder diagnosed in pregnancy after gestational diabetes. Available epidemiological data report widely varying prevalence rates of thyroid disorders during the antenatal period.

In normal gestation, the thyroid gland adapts its structure and function to satisfy increasing functional demand. Decreased thyroid reserve can lead to thyroid insufficiency that emerges during pregnancy.[1] The marked physiological changes that occur during normal pregnancy make it necessary to use specific TSH and free T4 (FT4) reference ranges, ideally population specific, to correctly assess thyroid function.[2]

Inadequate maternal thyroid hormone production, particularly during the first stages of gestation when the foetus is reliant on maternal thyroxine, has been associated with multiple obstetric and neonatal adverse outcomes,[3–6] including inadequate neuropsychological development in the offspring.[6–8] Even in the absence of thyroid dysfunction (TD), the presence of maternal antithyroperoxidase antibodies (TPO Ab) increases the risk of miscarriage and preterm delivery.[9] Despite this, universal screening of TD in pregnancy is not well established and targeted TSH testing for high-risk groups is recommended by international scientific society guidelines.[10,11] These guidelines consider maternal age over 30 years as a risk factor for hypothyroidism in pregnancy; however, this has not been supported in some large series.[12,13]

In this epidemiological study, we investigate the prevalence of thyroid disease in early pregnancy by universal screening of a cohort of Spanish women living in an iodine-sufficient area, applying population-specific TSH and FT4 reference ranges. We also analyse the relation between maternal age and risk of developing thyroid function abnormalities.