Levothyroxine dose adjustment in hypothyroid women achieving pregnancy through IVF

ObjectiveAbout one out of two women with primary hypothyroidism has to increase the dosage of exogenous levothyroxine (l-T4) during pregnancy. Considering the detrimental impact of IVF on thyroid function, it has been claimed but not demonstrated thatl-T4dose adjustment may be more significant in hypothyroid women who become pregnant after IVF.DesignRetrospective cohort study.MethodsHypothyroid-treated women who achieved a live birth through IVF were reviewed. Women could be included if thyroid function was well compensated withl-T4before the IVF cycle (i.e., serum TSH 4within the normal range). Serum TSH and dose adjustment were evaluated at five time points during pregnancy. The trimester ranges for serum TSH considered as reference to adjustl-T4therapy were 0.1–2.5 mIU/l for the first trimester, 0.2–3.0 mIU/l for the second trimester, and 0.3–3.0 mIU/l for the third trimester.ResultsThirty-eight women were selected. During the whole pregnancy 32 women (84%; 95% CI: 72–96%) required an increase in the dose ofl-T4. In most cases (n=28), this occured within the first 5–7 weeks of gestation (74%, 95% CI: 58–85%). At 5–7 weeks of gestation, the median (interquartile range) increase ofl-T4dose for the whole cohort was 26% (0–50%). At 30–32 weeks, it was 33% (14–68%). In order to identify predictive factors of dose adjustment, we compared women who did (n=28) and did not (n=10) adjustl-T4dosage at 5–7 weeks' gestation. Significant differences emerged for thyroid autoimmunity prevalence and for the distribution of hypothyroidism aetiology.ConclusionsThe vast majority of hypothyroid-treated women who achieve pregnancy through IVF need an increase in thel-T4dose during gestation. This requirement tends to occur very early during gestation.