Objective: To investigate the management of thyroid replacement during pregnancy in women who were prescribed thyroxine prior to pregnancy.
Design: Record-linkage technology was used retrospectively to identify pregnant women who were prescribed thyroxine in the general population of Tayside, Scotland.
Patients: All pregnant women who were 18 years and above and who delivered between 1st January 1993 and 31st March 2011 in Tayside were identified. Patients were included in the study if they have had at least three thyroxine prescriptions prior to pregnancy of which at least one prescription was within 6 months prior to pregnancy. Patients who delivered before 10 weeks of gestation were excluded from the study. Outcome measures: The number of TSH assay performed during pregnancy and the changes in dosage of thyroxine prescribed during pregnancy.
Results: We identified 950 pregnancies that had thyroxine prescribed prior to pregnancy. Overall, 96.9% of these pregnancies had at least one TSH assay performed during or just prior to pregnancy, with 81.2% in the first trimester. Mean TSH concentration declined after 8 weeks gestation. The prescription of thyroxine was increased in 56.7% at any time during pregnancy and in 29.8% of pregnancies during the first trimester. Of 3661 TSH assays performed in 950 pregnancies, 19% were elevated. Overall 41% of pregnancies had at least one elevated serum TSH during pregnancy and 35% had at least one elevated TSH in the first trimester.
Conclusion: The serum TSH concentration is raised in many pregnancies. Development of pre-conception care for thyroid disease may improve the management of thyroid disease during pregnancy.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.