IVF outcome in treated hypothyroidism

Study question: Does adequate levothyroxine treatment overcome the detrimen tal effects of hypothyroidism on IVF outcome? Summary answer: An adequate levothyroxine treatment maintaining TSH serum levels below 2.5 mIU/L fully overcomesthe detrimental effects of hypothy roidism on IVF outcome. What is known already: Levothyroxine was shown to enhance the chances of pregnancy in women with hypothyroidism undergoing IVF. Nevertheless, the magnitude of these benefits has been questioned by a recent study that documen ted a worse IVF outcome in women with treated hypothyroidism. The available studies, however, have some important methodological limitations. In particular, levothyroxine treatment is not adjusted in accordance with the latest guidelines that recommends to maintain serum TSH below 2.5 mIU/L. Study design, size, duration: Retrospective review of women undergoing IVF during a three years period. Cases were women with clinical or subclinical treated hypothyroidism and serum TSH between 0.4 and 2.5 mIU/L. Controls were the two subsequent age-matched euthyroid women who had never assumed levothyroxine. Participants/materials, setting,methods:One hundredthirty-seven women sat isfied our selection criteria. Seventy-nine cases (58%) were thyroid antibodies positive. The number of treated women because of overt hypothyroidism and sub clinical hypothyroidism was 70 (51%) and 67 (49%), respectively. These cases were matched to 274 controls. Main results and the role of chance: Most IVF outcome variables were similar between the two study group with the exception of a higher cancellation rate for poor response (3.6% versus 0.7%, p ¼ 0.04), a longer COH duration (10.9+ 2.2 versus 10.1+2.0 days, p ¼ 0.001), a higher proportion of women failing to obtain viable embryos (17% versus 7%, p ¼ 0.006) and a lower fertilization rate (75% versus 86%, p ¼ 0.017) among cases. Conversely, the clinical preg nancy rate per started cycle (36% versus 34%, p ¼ 0.93), the implantation rate (28% versus 22%, p ¼ 0.11) and the live birth rate per started cycle (30% versus 27%, p ¼ 0.50) did not differ between cases and controls, respectively. Subgroup analyses comparing women with and without thyroid autoimmunity and women with overt and subclinical hypothyroidism failed to identify relevant differences. Limitations, reason for caution: The control group was matched by age and study period but we cannot completely rule out some confounders. Control women were not screened for thyroid antibodies and therefore we cannot exclude that some of them were positive. This possibility is however uncommon in women with serum TSH ≤ 2.5 mIU/L. Wider implications of the findings: Women scheduled for IVF with adequately treated hypothyroidism can be reassured regarding the outcome of the procedure. Indeed, an appropriate treatment maintaining serum TSH below the threshold value of 2.5 mIU/L fully overcomes the detrimental effects of hypothyroidism on the rate of success. Study funding/competing interest(s): None Trial registration number: Not applicable