Correlation of thyroid stimulating hormone (TSH) level with pregnancy outcome in women undergoing in vitro fertilization

Objective The aim of this study was to determine if pregnancy outcome for women undergoing in vitro fertilization is correlated with pre-conception thyroid-stimulating hormone level. Study design We performed a retrospective cohort study of in vitro fertilization cycles in our private practice with an initial positive serum human chorionic gonadotropin level and thyroid-stimulating hormone level available (n = 364). We examined whether or not birth outcome differed between cycles in which the thyroid-stimulating hormone was >2.5 mIU/L compared with cycles with a thyroid-stimulating hormone level of ≤2.5 mIU/L. Logistic regression was used to determine the association between thyroid-stimulating hormone level and spontaneous abortion rate. Results Delivery outcome was available for 195 cycles, 36% of which had a thyroid-stimulating hormone level >2.5. The gestational age at delivery was higher in cycles with a thyroid-stimulating hormone ≤2.5 than for cycles with a thyroid-stimulating hormone >2.5 (38.5 vs 38.0 weeks for singletons, 36.0 vs 34.6 weeks for twins, overall P = .012 for thyroid-stimulating hormone level). The mean birth weight for cycles with a thyroid-stimulating hormone ≤2.5 was higher than for cycles with a thyroid-stimulating hormone >2.5 (7.33 vs 6.78 lbs for singletons, P = .024 and 5.36 vs 4.83 lbs for twins, P = .023). Restricting analysis to cycles where the woman was not taking thyroid replacement did not change the overall conclusions. There was a trend toward increasing risk of miscarriage with increasing thyroid-stimulating hormone level in nondonor cycles, controlling for age and day 3 follicle-stimulating hormone level, but this trend did not reach statistical significance. Conclusion A pre-conception thyroid-stimulating hormone level >2.5 mIU/L is associated with a lower gestational age at delivery and lower birth weight in women undergoing in vitro fertilization.