Current (2011) guidelines from the American Thyroid Association include age over 30 as one of the risk factors for hypothyroidism in pregnancy. To verify whether age increases the risk of autoimmune thyroid disease in pregnancy, the Prague-based team performed a cross-sectional study of 5223 unselected pregnant women who were screened for thyroid disease in the first trimester between 2006 and 2008. The average age of the women was 31.
According to a report online March 21 in the Journal of Clinical Endocrinology and Metabolism, 857 of the women (16.4%) screened positive; 294 (5.6%) had TSH elevation, 146 (2.8%) had TSH suppression, 561 (10.7%) were positive for autoantibodies against thyroperoxidase (TPOAb) and 417 (8.0%) were euthyroid and TPOAb positive.
The researchers say the prevalence of hypothyroidism was similar in women aged 30 and older and women younger than age 30 (5.5% and 5.8%, respectively; p=NS).
“Using a logistic regression model, we didn’t find any significant association between age and serum TSH suppression, TSH elevation, or TPOAb positivity, or between age and TSH elevation with TPOAb positivity,” they write.
They say, to their knowledge, “this is the first large study to show that the prevalence of autoimmune thyroid disease does not increase with age in pregnant women and age over 30 cannot be regarded as a risk factor for hypothyroidism in pregnancy.”
In an email to Reuters Health, first author Dr. Eliska Potlukova from 3rd Department of Medicine, General University Hospital and 1st Faculty of Medicine, Charles University said: “Although generally the incidence of autoimmune thyroid disorders increases with age, especially after age 50, this is not the case in pregnant women. Therefore, a young pregnant women has the same risk of having hypothyroidism as an ‘elder’ (>30 year old) pregnant women. Thus, if you are a clinician deciding whether to measure TSH (and eventually TPOAb as well) in a pregnant women, you should not think – ‘she is only 24, therefore her risk of autoimmune thyroid disease is negligible’.”
Reached for comment on the Prague study, Dr. John H. Lazarus from the Centre for Endocrine and Diabetes Sciences, University Hospital of Wales, Cardiff, United Kingdom, told Reuters Health by email the ATA guideline that lists age over 30 as a risk factor for hypothyroidism, “probably needs revision (i.e., hypothyroidism could appear at any age).” Dr. Lazarus was not involved in the study.
As an aside, Dr. Potlukova said she regards the absence of a recommendation for TPOAb screening as a “major objection to the current guidelines.”
“TPOAb-positivity may have major clinical impact on the course of pregnancy also due to a decreased thyroid functional reserve. We show that TPOAb-positivity has an equally high incidence in young and elder pregnant women.”