Is Age a Risk Factor for Hypothyroidism in Pregnancy? An Analysis of 5223 Pregnant Women

CONTEXT:
The guidelines of American Thyroid Association from 2011 include age over 30 as one of the risk factors for hypothyroidism in pregnancy.
OBJECTIVE:
Our objective was to verify whether age increases the risk of autoimmune thyroid disease in pregnancy.
DESIGN:
We performed a cross-sectional study in 2006-2008 with laboratory assessment in a single center using primary care gynecological ambulances in cooperation with a referral center.
PATIENTS:
The study included 5223 consecutive pregnant women in gestational wk 9-12.
MAIN OUTCOME MEASURE:
We assessed the occurrence of pathological serum concentrations of TSH and/or antibodies against thyroperoxidase (TPOAb) with regard to age. Reference interval for TSH was 0.06-3.67 mU/liter; the upper cutoff value for TPOAb was 143 kU/liter.
RESULTS:
Overall, 857 women (16.4%) were positively screened. Of these, 294 (5.63%) had TSH elevation, 146 (2.79%) had TSH suppression, 561 (10.74%) were TPOAb positive, and 417 (7.98%) were euthyroid and TPOAb positive. The average age of women was 31.1 yr. The prevalence of hypothyroidism was 5.5 and 5.8% in women aged 30 or older and those under 30 yr, respectively (P value nonsignificant). Using a logistic regression model, we didn't find any significant association between age and serum TSH suppression, TSH elevation, or TPOAb positivity (P = 0.553, P = 0.680, and P = 0.056, respectively) or between age and TSH elevation with TPOAb positivity (P = 0.967). In a subgroup analysis of risk factors for hypothyroidism in 132 hypothyroid women, addition of age 30 or older increased the proportion of women identified in a case-finding screening strategy from 55.3 to 85.6%.
CONCLUSIONS:
Prevalence of autoimmune thyroid disease does not increase with age in pregnant women; however, addition of age 30 or over to the case-finding screening strategy may substantially improve its efficiency due to a larger number of women screened.