Untreated Subclinical Hypothyroidism (TSH <6.0 mIU/L) Does Not Adversely Affect ART Live Birth Rates
Background
The management of subclinical hypothyroidism (SCH), characterized by elevated thyroid-stimulating hormone (TSH) but normal free thyroxine, remains a significant area of uncertainty in reproductive medicine. Specifically, for women undergoing assisted reproductive technology (ART), the optimal TSH threshold for intervention and the impact of mild, untreated SCH on fertility outcomes are debated. Current guidelines vary, leading to inconsistent clinical practice and potential overtreatment. This study addresses the critical gap in understanding whether untreated SCH, with TSH levels below 6.0 mIU/L, negatively impacts ART success.
Study Design
Researchers conducted a retrospective cohort study using data from 944 women screened for thyroid function and thyroid peroxidase antibodies (TPOAb) during the TABLET trial (June 2012-December 2013) at Birmingham Women's Hospital, UK. Of these, 560 women had complete outcome data. Women with TSH ≥6.0 mIU/L received levothyroxine and were excluded from the primary analysis of untreated SCH. The main comparison evaluated 'total SCH' (TSH >3.63 mIU/L) against 'euthyroid-1' (TSH 0.44-3.63 mIU/L). Subgroup analyses further compared 'untreated SCH' (TSH 3.64-5.99 mIU/L) to 'euthyroid-1' women, and 'untreated high-normal-mild SCH' (TSH 2.5-5.99 mIU/L) to a stricter 'euthyroid-2' threshold (TSH 0.44-2.5 mIU/L). Multivariable logistic regression adjusted for confounders, with live birth as the primary outcome.
Results
Among the 560 women with outcome data, 60 had subclinical hypothyroidism. While SCH was associated with fewer oocytes retrieved (9.0 vs 10.4, p = 0.02) and fewer mature oocytes (7.4 vs 8.4, p = 0.05), these differences did not translate into a reduced live birth rate.
No significant difference in live birth was observed across any of the comparisons: 'untreated SCH' vs euthyroid-1 yielded an adjusted odds ratio (aOR) of 1.01 (95% CI 0.54-1.87, p = 1.0), and 'untreated high-normal-mild-SCH' vs euthyroid-2 showed an aOR of 0.96 (95% CI 0.65-1.42, p = 0.8). Intriguingly, in women with untreated SCH who achieved live birth, TSH levels normalized spontaneously in 8/15 cases, and no adverse pregnancy outcomes were reported. These findings suggest that mild elevations in TSH below 6.0 mIU/L do not negatively impact the ultimate success of ART.
Key Findings
- Untreated subclinical hypothyroidism (TSH <6.0 mIU/L) did not significantly reduce live birth rates in ART patients (aOR 1.01, p=1.0).
- SCH was associated with fewer oocytes retrieved (9.0 vs 10.4, p=0.02) and mature oocytes (7.4 vs 8.4, p=0.05).
- TSH levels spontaneously normalized in 8/15 cases of untreated SCH women who achieved live birth.
- No adverse pregnancy outcomes were observed in women with untreated SCH who achieved live birth.
Why It Matters
This study provides crucial evidence suggesting that untreated preconception subclinical hypothyroidism with TSH <6.0 mIU/L may not adversely affect ART outcomes or live birth rates. For individuals undergoing ART with mild TSH elevations, this could alleviate concerns about the need for immediate levothyroxine treatment, potentially reducing unnecessary medication burden and associated costs or anxieties. The finding that TSH can normalize spontaneously in successful pregnancies further supports a less aggressive management approach for mild SCH in this context. While the impact on oocyte quantity warrants further investigation, the ultimate goal of live birth appears unaffected. This research could inform future clinical guidelines, promoting a more nuanced, evidence-based approach to thyroid management in fertility clinics.
subclinical hypothyroidism
assisted reproductive technology
art
tsh
fertility
live birth