Higher TSH within the normal range is independently associated with reduced IVF clinical pregnancy odds: a K-means cluster analysis challenging the binary cutoff paradigm
Year: 2026
Type: article
Study design: Observational Study
Abstract: Background The impact of thyroid-stimulating hormone (TSH) variation within the normal reference range on IVF outcomes remains controversial, with prior studies yielding conflicting results. Methods We conducted a retrospective cohort study of 878 euthyroid women (TSH 0.25–4.0 µIU/mL) undergoing fresh IVF/ICSI cycles at Al-Hayat Hospital, Iraq (2022–2024). Patients were classified into four groups using k-means clustering of serum TSH values: Cluster 1 (2.9–4.0 µIU/mL), Cluster 2 (2.2–2.8 µIU/mL), Cluster 3 (1.4–2.0 µIU/mL), and Cluster 4 (0.25–1.3 µIU/mL). Clinical, hormonal, and embryological parameters were compared across clusters, and stepwise logistic regression was performed to adjust for confounders. Results Clinical pregnancy was achieved in 474/878 women (54%). As expected, women with pregnancy were younger (30.1 ± 5.1 vs. 31.2 ± 5.5 years, p = 0.003) and had lower mean TSH (1.95 ± 0.85 vs. 2.08 ± 0.96 µIU/mL, p = 0.030). Ovarian reserve and response markers were higher in the pregnancy group, including antral follicle count (AFC) (11.3 ± 4.2 vs. 10.4 ± 4.2, p = 0.001), preovulatory follicle count (PFC) (11.9 ± 4.2 vs. 11.0 ± 4.2, p = 0.003), and oocyte yield (10.4 ± 5.0 vs. 9.6 ± 4.8, p = 0.010). Oocyte maturation (80.5 ± 15.5% vs. 76.9 ± 17.1%, p = 0.003) and fertilization rates (88.0 ± 14.0% vs. 84.2 ± 16.9%, p = 0.003) were also significantly higher, while women without pregnancy required more ampoules (41.2 ± 18.8 vs. 36.6 ± 16.5, p < 0.001). Stepwise regression identified age (OR = 0.97, p = 0.059), ampoules (OR = 0.99, p = 0.024), oocyte yield (OR = 1.04, p = 0.014), maturation rate (OR = 1.10, p = 0.002), fertilization rate (OR = 1.06, p = 0.015), and TSH clusters as independent predictors. Cluster 3 (TSH 1.4–2.0 µIU/mL) showed the highest pregnancy rate (58.2%), while Cluster 1 (TSH 2.9–4.0 µIU/mL) had the lowest (42.7%) and was independently associated with reduced odds (OR = 0.53, 95% CI 0.35–0.80, p = 0.0024). Subgroup analysis revealed that unexplained and ovarian factor infertility were most sensitive to thyroid variation, whereas male factor infertility remained stable and PCO cases diverged. Conclusions K-means clustering revealed that women with higher-normal TSH (Cluster 1: 2.9–4.0 µIU/mL) had independently reduced odds of clinical pregnancy (OR = 0.53, 95% CI 0.35–0.80, p = 0.002) compared with Cluster 3 (1.4–2.0 µIU/mL), challenging the adequacy of a single binary cutoff and supporting individualized, data-driven thyroid assessment in IVF.
Source: Frontiers in Endocrinology
Authors: Mohamed M. Amin, SI. Hassanein
Institution: German University in Cairo
Language: English
Subfield: Endocrinology, Diabetes and Metabolism
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $3,801
OpenAlex ID: W7223286528