A re-look at the relevance of TSH and thyroid autoimmunity for pregnancy outcomes: Analyses of RCT data from PPCOS II and AMIGOS.

Objective: We examined if thyroid autoimmunity is relevant to the relationship between maternal TSH levels and pregnancy outcomes.

Design: Retrospective cohort analysis of data from two randomized controlled trials (RCTs).

Subjects: Participants of the Pregnancy in Polycystic Ovary Syndrome (PPCOS II, n = 746) and the Assessment of Multiple Intrauterine Gestations from Ovarian Stimulation (AMIGOS, n = 832 with unexplained infertility) RCTs.

Exposure: Pre-trial intervention levels of thyroid stimulating hormone (TSH) at threshold of ≥2.0 mU/L and thyroid peroxidase antibody (TPO-Ab) at titer threshold of ≥30 U/mL.

Main Outcome: Live birth (primary outcome), pregnancy loss and preterm birth (secondary outcomes). Generalized linear model (GLM) analyses examined the relationship between exposure to TSH and TPO-Ab at specified thresholds with the specified outcomes; covariates adjusted for included age, body mass index, race, ethnicity, education, smoking, duration of infertility, PCOS (versus unexplained infertility) and randomized intervention arm in the respective RCTs.

Results: On adjusted analyses, live birth was significantly reduced in the exposed population (those with TSH ≥2.0 mU/L and TPO-Ab ≥30 U/mL, n= 117/1578, 7.4%, adjusted risk ratio [ARR] 0.55, 95% CI 0.35- 0.87) compared to the unexposed (those with TSH <2.0 mU/L and TPO-Ab <30 U/mL, n=865/1578, 54.8%). Furthermore, the risk of pregnancy loss and of early preterm birth (<32 weeks) was significantly higher in the exposed compared to the unexposed (ARR for pregnancy loss was 1.66, 95% CI 1.14- 2.42, and ARR for early preterm birth was 4. 82 (95% CI 1.53- 15.19).

Conclusions: In women with TPO-Ab titers ≥30 U/mL, pregnancy outcomes may be compromised at TSH threshold of ≥2 mU/L. These findings of an interaction between TSH and TPO for pregnancy outcomes merit further investigation in prospective studies.