Leonie Warringa1, Joris Osinga1, Sjoerd van den Berg1, Robin Peeters1, Tim Korevaar1
(1) Erasmus MC, Rotterdam, Netherlands.
Background:
Both overt and subclinical thyroid disease are associated with adverse pregnancy outcomes such as miscarriage, preterm birth and pre-eclampsia. It remains unclear if thyroid function test abnormalities that are first diagnosed during pregnancy, result from the changes in gestational thyroid physiology or if they were already present prior to pregnancy and only diagnosed for the first time during pregnancy. However, preconception thyroid function data of women with gestational thyroid disease is scarce.
Methods:
This study included 2,718 women of the Generation R Next study, a population-based prospective cohort from pregnancy planning through postpartum in Rotterdam. The prevalence of abnormalities in thyroid function tests during both the preconception and gestational periods was assessed using various reference ranges, and individual trajectories were illustrated with Sankey diagrams. For those women with thyroid function test abnormalities in pregnancy, the mean thyroid hormones concentrations of preconception were determined.
Results:
A subgroup of 503 women had thyroid function measurement during preconception and subsequent pregnancy. The median interval between the thyroid function measurements was 4.2 months (95% range 0.9-13.0). The overall prevalence of thyroid function test abnormalities was largely consistent during preconception and pregnancy. However, when assay cutoffs are applied during pregnancy, prevalence of e.g. subclinical hyperthyroidism changed from 1.4% to 8%. Women with (subclinical) hypothyroidism or hypothyroxinemia during pregnancy had a higher preconception TSH than euthyroid pregnant women (3.08 mU/L, 3.83 mU/L and 2.25 mU/L vs. 1.65 mU/L) and women with hyperthyroidism during pregnancy had a significant lower preconception TSH (0.53 mU/L vs. 1.65 mU/L).
Conclusion:
This is the first study to show that thyroid function test abnormalities identified during pregnancy are predominantly likely to present pre-existing thyroid disease rather than a failure to adapt to gestational thyroid physiological changes.