IMPORTANCE Differentiated thyroid cancer (DTC) is commonly diagnosed in women of child-bearing age, but whether pregnancy influences the prognosis of DTC remained controversial.

OBJECTIVE This systematic review and meta-analysis aimed to summarize and appraise the existing evidence of the impact of pregnancy on the prognosis of patients previously treated for DTC.

DATA SOURCES We searched PubMed, Embase, Web of Science, Cochrane, and Scopus until February 2023.

STUDY SELECTION Studies of patients diagnosed and treated for DTC before pregnancy reporting the recurrence/progression condition of DTC were included. Case reports and studies failing to identify the time of diagnosis or initial treatment were excluded.

DATA EXTRACTION AND SYNTHESIS Meta-analyses were conducted according to MOOSE guideline. Data extraction was conducted by two independent investigators with a standard form. Pooled effect estimates were calculated in a random-effects model.

MAIN OUTCOMES AND MEASURES DTC recurrence/progression and the type of recurrence/progression (structural or biochemical).

RESULTS Among the 10 included studies (n = 625), 4 (n = 143) of them compared the pregnancy group with the non-pregnancy group while the remaining 6 (n = 482) only included the pregnant patients. The pooled proportion of recurrence/progression in all pregnant patients was 13% (95% CI, 6%, 25%). Compared with the non-pregnancy group, the pooled odds ratio of recurrence/progression in the pregnancy group was 0.75 (95% CI, 0.45, 1.23). Two included studies focused on patients with distant metastasis and also did not observe difference in disease recurrence/progression between the pregnancy group and the non-pregnancy group [OR, 0.51 (95% CI, 0.14-1.87)]. Six included studies also reported response to therapy status prior to pregnancy, and the pooled proportion for recurrence/progression in pregnant DTC patients with excellent response (n=287), indeterminate response (n=44), biochemical incomplete response (n=41) and structural incomplete response (n=70) was 0.00 (95% CI, 0.00-0.86), 0.09 (95% CI, 0.00-0.99), 0.20 (95% CI, 0.06-0.46) and 0.45 (95% CI, 0.17-0.76), respectively. There was a trend for an increasingly higher risk of recurrence/progression from excellent, indeterminate, biochemical incomplete to structural incomplete response to therapy (P<0.05).

CONCLUSIONS AND RELEVANCE Pregnancy appears to have a minimal impact on the prognosis of DTC with initial treatment. Clinicians may pay more attention to the progression of DTC among pregnant women with biochemical and/or structural persistence.

Question Does subsequent pregnancy has an impact on the prognosis of patients previously treated for differentiated thyroid cancer (DTC)?

Findings In this systematic review and meta-analysis of 10 studies including 625 patients previously treated for DTC and underwent pregnancy subsequently, pregnancy might have a minimal impact on DTC recurrence/progression. Patients with biochemical and/or structural incomplete response to DTC treatment prior to pregnancy appears to have a higher risk of DTC recurrence/progression compared to those with excellent or indeterminate response.

Meaning Though pregnancy appears to have little influence on the prognosis of patients previously treated for DTC, patients with biochemical and/or structural persistence should be more carefully monitored during pregnancy.

The authors have declared no competing interest.

The study was funded by the National Natural Science Foundation of China (81903433) and the Fundamental Research Funds for the Central Universities (BMU2021YJ030).

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↵# Co-first authors

Funding: The study was funded by the National Natural Science Foundation of China (81903433) and the Fundamental Research Funds for the Central Universities (BMU2021YJ030).

Author Disclose Statement: The authors have nothing to disclose.

All data produced in the present work are contained in the manuscript