Incidence of elevation of serum thyroid-stimulating hormone during controlled ovarian hyperstimulation for in vitro fertilization

Objective: To evaluate the rate of euthyroid women encountering an elevation of serum TSH above the threshold of 2.5 mIU/L during controlled ovarian hyperstimulation (COH) for IVF.

Study design: Six-month prospective cohort study on 175 consecutive euthyroid women undergoing their first IVF cycle. Serum TSH assessments were performed before COH, at the time of hCG administration and at +16 days after hCG administration. Women were eligible if serum TSH tested the month preceding the IVF cycle was 0.4-2.5 mIU/L. A history of thyroid disorders was an exclusion criterion.

Results: Serum concentrations of TSH at the three scheduled assessments were 1.5±0.5, 2.2±1.0 and 2.1±1.1 mIU/L, respectively. A statistically significant increase occurred between basal levels and levels at the time of hCG administration (p<0.001). Afterwards, levels remained stable (p=0.49). Serum TSH at the time of hCG administration exceeded the threshold of 2.5 mIU/L in 61 subjects, corresponding to 35% (95% CI: 28-42%). At +16 days after hCG administration, this event was observed in 47 subjects (27%, 95% CI: 21-34%). Baseline characteristics of women who did and did not exceed the threshold were similar apart from basal serum TSH, which was higher in the former group. The OR was 7.6 (95%CI: 2.9-20.2) per mIU/L (p<0.001). Cycle outcome and pregnancy rate were also similar.

Conclusion: Serum TSH exceeds the threshold of 2.5 mIU/L during COH in one out of three women who are euthyroid prior to enter an IVF cycle. Further evidence is warranted to elucidate the clinical relevance of our findings.