Endocrine Abstracts

Context: High maternal TSH and/or low FT₄ during pregnancy is associated with an increased risk of premature delivery. hCG is the main determinant of thyroid function changes during pregnancy but has a versatile pattern with high inter and intra-individual variability. We hypothesised that the correct interpretation of thyroid function tests and its use in the risk assessment of premature delivery during pregnancy depend on hCG levels.

Design, setting, and participants: TSH, FT₄, hCG, and TPO-antibody levels were available in 5956 women. In logistic regression models for premature delivery we tested for interaction between TSH or FT₄ and hCG and when significant analyses were stratified. All analyses were adjusted for maternal age, smoking, education level, ethnicity, parity, BMI, height, and foetal gender.

Results: The association between TSH levels and premature delivery was different according to hCG levels (P interaction=0.02). The risk of premature delivery in women with high TSH levels ≥85th, ≥90th, or ≥95th percentile but low hCG levels was decreased by 47, 61, and 18% respectively. The risk of premature delivery in women with high TSH levels ≥85th, ≥90th, or ≥95th percentile but high hCG levels was increased two-, 3.1-, and 6.1-fold respectively (P low vs high <0.001). The association between FT₄ levels and premature delivery was not different according to hCG levels (P interaction=0.23). However, women with very low FT₄ levels (≤3rd percentile) had different risks for premature delivery according to hCG (low to high OR 1.99–3.11; P=0.02). All results remained similar after exclusion of TPOAb positive women, women with preeclampsia or amongst women with spontaneous premature delivery only.

Conclusion: The addition of hCG may improve the risk assessment of premature delivery according to TSH. High TSH levels despite high hCG levels reflect the inability of thyroid function to increase according to hCG stimulation. This inability to increase is a novel risk factor for premature delivery. Future studies are needed to replicate these results and incorporate these findings into clinical decision models.

Disclosure: This work was supported by a clinical fellowship from ZonMw, project number 90700412 (R Peeters).