Association of thyroid carcinoma with pregnancy: A meta-analysis

A number of scholars reported that reproductive factors play a significant role in thyroid cancer and the correlation between the two may affect the diagnosis and treatment of thyroid carcinoma during pregnancy. To determine whether pregnancy reproductive factors affect thyroid carcinoma, we conducted a meta-analysis of studies that investigated the association between pregnancy factors and thyroid carcinoma. PubMed, OVID and the Cochrane Library were searched from their inception to April 1st, 2013. The searched publications mainly investigated reproductive factors and the morbidity or prognosis of female thyroid carcinoma. The studies were filtered by predetermined standards and the quality of the included studies was evaluated by the Newcastle-Ottawa scale inventory. Two researchers independently extracted information on first author, year of publication, study design (case-control or prospective cohort), compared populations, inclusion and exclusion criteria and total sample size. Other researchers assessed the studies for publication bias and performed statistical analyses. Discrepancies were resolved by consensus. A total of 21 studies were selected for the meta-analysis, including 406,329 cases in total. Compared to the control group, the risk of thyroid carcinoma in women with a history of pregnancy was not significantly discrepant, [odds ratio (OR)=1.00, 95% confidence interval (CI): 0.91-1.11]. However, the risk of thyroid carcinoma in women with a history of ≥ 3 pregnancies was significantly increased (OR=1.39, 95% CI: 1.21-1.59). Furthermore, an interval of ≤ 5 years since the last pregnancy was closely associated with thyroid carcinoma (OR=1.53, 95% CI: 1.29-1.81). The patients developed thyroid carcinoma during pregnancy did not exhibit an increased risk of lymphatic metastasis (OR=0.94, 95% CI: 0.53-1.67); the risk of distant metastasis also did not increase significantly (OR=1.03, 95% CI: 0.86-1.24). Therefore, multiple pregnancies and a ≤ 5-year interval between pregnancies were identified as high-risk factors for thyroid carcinoma, whereas thyroid carcinoma during pregnancy was not associated with a significant risk of lymphatic and distant metastasis.