Abstract Context Most studies of thyroid function changes during pregnancy use a cross-sectional design comparing means between groups rather than similarities within groups. Objective Latent class growth analysis (LCGA) is a novel approach to investigate longitudinal changes that provide dynamic understanding of the relationship between thyroid status and advancing pregnancy. Design Prospective observational study with repeated assessments Setting General community Patients 1100 healthy pregnant women who were included at their first antenatal visit at 12 weeks gestation Main outcome measures Statistically defined distinct groups based on determined specific changing trajectories by LCGA of both fT4 and TSH at each trimester. Results LCGA revealed three trajectory classes. Class 1 (n = 1019, 92.4%), a ‘Low increasing TSH’ reference group, had a gradual increase in TSH throughout gestation (from 1.1 to 1.3 IU/l). Class 2 (n = 30, 2.8%), ‘High increasing TSH’’, displayed the largest increase in TSH (from 1.9 to 3.3 IU/l); Class 3 (n = 51, 4.6%), ‘Decreasing TSH’, had the largest fall in TSH (from 3.2 to 2.4 IU/l). (Sub)clinical hypothyroidism at 12 weeks occurred in up to 60% of class 3 women and was accompanied by elevated TPO-Ab titres (50%) and a parental history of thyroid dysfunction (23%). 70% of class 2 women were nulliparous compared to 46% and 49% in classes 1 and 3. Conclusion LCGA revealed distinct trajectories of longitudinal changes of fT4 and TSH levels during pregnancy in 7.4% of women. These trajectories were correlated with parity and TPO-Ab status and followed patterns that might reflect differences in pregnancy-specific immune tolerance between nulliparous and multiparous women. Copyright © 2018 Endocrine Society
Journal of Clinical Endocrinology and Metabolism – Oxford University Press
Published: May 28, 2018
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