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 < or = 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 < or = 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 < or = 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.