Endocrine Abstracts

Context/Objective: Evidence on the impact of thyroid hormone treatment (LT4) on pregnancy outcomes in women with subclinical hypothyroidism (SCH) without TPOAb remains scarce. We assessed this relationship in a single centre in a real-world setting.

Design, Setting, Participants: Cross-sectional study in 1460 women screened for TSH, free T4 and thyroid peroxidase antibodies (TPOAb) at median 13 (11-17) weeks of gestation, during the period 2013-2014. Exclusion criteria were twin and assisted pregnancies, women treated with LT4 before screening, overt hyperthyroidism, TPOAb positivity and hypothyroxinaemia. The impact of LT4 on pregnancy outcomes was investigated in group of 53 women with SCH (TSH ≥3.74); LT4 was initiated at median 13 (10-22) weeks and at a mean dosage of 45.3 ± 16.3 μg/day. Women with SCH and not treated with LT4 served as controls (n=18). The prevalence of pregnancy morbidities in these two groups was compared with that in a reference (REF) group of 1389 women (TSH<3.74 mIU/l) using a χ2 test; results were adjusted for confounders and a p-value ≤0.025 was considered as significant.

Results: In the SCH control group, the prevalence of pre-eclampsia and gestational diabetes was (borderline and significantly) higher vs that in the REF group (16.7% vs 5.0%; P=0.026 and 27.8% vs 18.9%; P=0.014) but in the SCH treated group comparable vs the REF group (7.6% vs 5.0% and 22.6% vs 18.9%; P=0.610 and 0.547, respectively). The prevalence’s of the other outcomes (preterm birth, blood loss at birth, emergency C-section and altered birth weight) were comparable between the intervention and REF group.

Conclusions: Women with SCH without TPOAb had a higher prevalence of pre-eclampsia and GDM compared with euthyroid women. However, in women with treated SCH, the prevalence of those outcomes was comparable with that in the euthyroid reference group, even when treatment was started late first / early second trimester. This is the first real-world study that shows a beneficial impact of LT4 on clinical pregnancy outcomes and therefore, adds some evidence to the current guidelines, proposing to treat women with SCH and no TPOAb.