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Clin Epidemiol. 2018 Dec 3;10:1801-1816. doi: 10.2147/CLEP.S175616. eCollection 2018.

Maternal use of thyroid hormone replacement therapy before, during, and after pregnancy: agreement between self-report and prescription records and group-based trajectory modeling of prescription patterns.

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Pharmacoepidemiology and Drug Safety Research Group, School of Pharmacy, University of Oslo, 0316 Oslo, Norway,
Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA,
Department of Statistical Science, Cornell University, Ithaca, NY 14853, USA.
Department of Child Health and Development, National Institute of Public Health, 0403 Oslo, Norway.



A reliable definition of exposure and knowledge about long-term medication patterns is important for drug safety studies during pregnancy. Few studies have investigated these measures for thyroid hormone replacement therapy (THRT). The purpose of this study was to 1) calculate the agreement between self-report and dispensed prescriptions of THRT and 2) classify women with similar adherence patterns to THRT into disjoint longitudinal trajectories.


Our analysis used data from the Norwegian Mother and Child Cohort Study (MoBa), a prospective population-based cohort study. MoBa was linked to prescription records from the Norwegian Prescription Database (NorPD). We estimated Cohen's kappa coefficients (k) and approximate 95% CIs for agreement between self-report and prescription records for the 6-month period prior to pregnancy and for each pregnancy trimester. Using group-based trajectory models (GBTMs), we estimated adherence trajectories among women who self-reported and had a THRT prescription.


There were 56,148 women in MoBa, who had both a record in NorPD and available prescription history up to 1 year prior to pregnancy. Of these, 1,171 (2.1%) self-reported and received a prescription for THRT. Agreement was "perfect" in the 6-month period prior to pregnancy (k=0.86; CI 0.85-0.88), in the first (k=0.83; CI 0.82-0.85) and in the second trimesters (k=0.89; CI 0.87-0.90), while this was moderate (k=0.57; CI 0.54-0.59) in the third trimester. Among the subset of the 1,171 women, we identified four disjoint GBTM adherence groups: Constant-High (50.2%), Constant-Medium (32.9%), Increasing-Medium (11.0%), and Decreasing-Low (5.8%).


Agreement between self-report and prescription records was high for THRT in the early pregnancy period. Based on our GBTM results, about one in two women with hypothyroidism had adequate adherence to prescribed THRT throughout pregnancy. Given the potential consequences, evidence of low adherence in 5.8% of pregnant women with hypothyroidism is of concern.


MoBa; NorPD; group-based trajectory models; hypothyroidism; pregnancy; κ

Conflict of interest statement

Disclosure HN is a member of several nonprofit organizations. She is a board member of the Norwegian Pharmaceutical Society, member of the scientific board of the European Network of Teratology Information Services, chair of the Pregnancy Special Interest Group (SIG) and International Society of Pharmacoepi-demiology (ISPE), and member of the Executive Committee, European Drug Utilization Group (EuroDURG). She serves as an independent expert and a member of the Pharmacovigilance Risk Assessment Committee (PRAC) and European Medicines Agency (EMA). AL is the current head of Steering Committee of the Norwegian Society for Pharmacoepidemiology, which is a nonprofit organization for pharmacoepidemiologists in Nor-way. ASF, AL, and HN are part of the PharmacoEpidemiology and Drug Safety Research Group (PharmaSafe). PharmaSafe is a member of the European Network of Centers for Pharmacoepidemiology and Pharmacovigilance (EnCePP). DSM reports no conflicts of interest in this work.

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