Is age a risk factor for hypothyroidism in pregnancy? An analysis of 5223 pregnant women

The guidelines of American Thyroid Association from 2011 include age over 30 as one of the risk factors for hypothyroidism in pregnancy.

Our objective was to verify whether age increases the risk of autoimmune thyroid disease in pregnancy.

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.

The study included 5223 consecutive pregnant women in gestational wk 9-12.

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.

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%.

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.