Changes suggestive of post-partum thyroiditis in women with established hypothyroidism: incidence and predictors

Post-partum thyroiditis (PPT) is a common phenomenon in the general population. To date there have been few studies examining the incidence of PPT in women with hypothyroidism antedating pregnancy. This study aimed to assess the incidence and potential predictors of PPT in women with treated hypothyroidism antedating pregnancy.

Retrospective cohort study.

We compiled a cohort of 97 women with previous hypothyroidism antedating pregnancy seen in the Endocrinology in Pregnancy clinic from 1999 to 2011, collecting data on thyroid function, antibodies and levothyroxine doses post-partum. The incidence of PPT and its predictors were analysed.

A total of 66 (68%) women had fluctuations in thyroid function consistent with PPT. Of these, 22 (33%) had a hyperthyroid phase alone, 22 (33%) had a hypothyroid phase alone and 22 (33%) had both a hyper and hypo phase. The majority of women had their dose of thyroid medication adjusted during the PPT episode. Women who were on a full dose of thyroxine post-partum were significantly less likely to have a hypothyroid phase. In multivariable analysis, the only predictor of PPT was the presence of thyroid antibodies, with 83% of antibody positive women having PPT compared to 44% of antibody negative women (P = 0·0001).

In our cohort, 2/3 of women had fluctuations in thyroid function consistent with PPT and most required adjustment of their thyroid dose. Women with hypothyroidism antedating pregnancy are at high risk for PPT and should be closely monitored during the first year post-partum.