Postpartum thyroid function following LT4 treatment from infertility treatment to delivery in women with subclinical hypothyroidism or high-normal TSH: a retrospective study.

BACKGROUND

Levothyroxine (LT4) therapy is commonly initiated in women undergoing infertility treatment who have high-normal thyroid-stimulating hormone (TSH) levels (HN) or subclinical hypothyroidism (SCH). However, there are no clear postpartum management guidelines for these patients.

METHODS

We retrospectively analyzed 155 women (56 with HN, 99 with SCH) who initiated LT4 therapy during infertility treatment, discontinued it immediately after delivery, and underwent TSH measurement within 6 months postpartum. We evaluated postpartum TSH levels and their association with pre-treatment TSH, LT4 dose at delivery, thyroid volume, body weight, and thyroid autoantibodies. Receiver operating characteristic (ROC) curve analysis was performed to predict postpartum SCH.

RESULTS

Postpartum TSH levels were significantly lower than pre-treatment levels (median 2.57 vs. 4.30 mIU/L,  < 0.001). TSH remained within the reference range in 78% of participants, while 15.7% had SCH and 6.3% had thyrotoxicosis. Higher pre-treatment TSH and higher LT4 dose at delivery were significantly associated with postpartum SCH ( < 0.001 for both). ROC analysis identified cutoff values of 4.82 mIU/L for pre-treatment TSH (area under the curve [AUC] = 0.785) and 71.4 µg/day for LT4 dose (AUC = 0.753). Postpartum thyrotoxicosis occurred in 6.3% of participants, all of whom were antibody-positive. Only two women required LT4 resumption after one year postpartum due to TSH ≥ 10 mIU/L.

CONCLUSIONS

For women with HN or SCH who initiated LT4 therapy during infertility treatment, immediate discontinuation of LT4 after delivery appears generally safe. Nevertheless, postpartum thyroid function should be closely monitored, particularly in antibody-positive patients or those with elevated pre-treatment TSH.