The association of pregnancy with disease progression in patients previously treated for differentiated thyroid cancer: A propensity score-matched retrospective cohort study
Authors: Li Xin , Xiao Wu-Cai , Mei Fang , Shan Rui , Song Shi-Bing , Sun Bang-Kai , Bao He-Ling , Chen Jing , Yuan Chun-Hui , Liu Zheng 
Published: March 2023

AbstractIMPORTANCEDifferentiated thyroid cancer (DTC) is increasingly common in women of reproductive age. However, whether pregnancy increases the risk of progression/recurrence of DTC after treatment remains controversial due to the effect of confounding.OBJECTIVETo assess the effect of pregnancy on structural or biochemical progression in patients previously treated for DTC in a retrospective cohort using propensity score matching (PSM).DESIGN, SETTING, AND PARTICIPANTSThis cohort study included 123 pregnant women and 1,376 non-pregnant women after initial treatment for DTC at Peking University Third Hospital between January 2012 and December 2022. To control the effect of confounding, we carefully matched pregnancy (n = 102) and non-pregnancy groups (n = 297) in terms of age, Hashimoto’s thyroiditis, lymph node dissection, extra-thyroid invasion, initial risk of recurrence after treatment, and time interval between treatment and last follow up by using PSM.EXPOSURESDTC patients became pregnant after previous treatment.MAIN OUTCOMES AND MEASURESThe risk of structural or biochemical progression was assessed in the pregnancy and PSM matched non-pregnancy groups, respectively.Conditional logistics regression models were used to control important confounders and consider the matching properties of the data.RESULTSAt baseline, the pregnancy (n = 102) and non-pregnancy groups (n = 297) were balanced in all matched variables (standardized differences <10% andP> 0.05). After a mean follow-up of approximately 4.5 years, we observed no evidence of difference between the two groups in growth in the size of existing metastatic foci [2 (2.0 %) vs. 2 (0.7 %);P= 0.346], percentage of patients developing new lymph node metastases [4 (3.9 %) vs. 21 (7.1 %);P= 0.519], node growth in the contralateral thyroid lobe [4 (3.9 %) vs. 16 (5.4 %);P= 0.324 ], or biochemical progression [2 (2.0 %) vs. 9 (3.0 %);P= 0.583]. Results from conditional logistic regressions and several sensitivity analyses also showed no evidence of association of pregnancy with the risk of progression, after adjusting for potential confounders of age, tumor size, initial risk stratification, Hashimoto’s thyroiditis, lymph node dissection, the time interval between treatment and follow-up, and achievement of TSH inhibition target (P= 0.354). The pregnancy-progression association observed longer than 4.5 years showed no evidence of difference with that observed shorter than 4.5 years (Pfor interaction was 0.283). We further classified the pregnancy patients into 3 subgroups based on the time interval between treatment and pregnancy (< 1 year, 1-2 years, ≥ 2 years) and found that the shorter the time interval, the higher the risk of DTC progression (Pfor trend was 0.043).CONCLUSIONS AND RELEVANCEThe risk of DTC progression/recurrence in the pregnant women was not higher than that in the well-matched, non-pregnant women. For young women previously treated for DTC, disease progression might not be a concern for their future pregnancy plan, but it seems safer to wait an appropriate amount of time before pregnancy.Key PointsQuestionDoes pregnancy increase the risk of disease progression/recurrence in patients previously treated for differentiated thyroid cancer (DTC)?FindingsThis propensity score-matched retrospective cohort study included 399 patients previously treated for DTC. In a mean follow-up of approximately 4.5 years, the risk of progression in the pregnant group was not higher than the well-matched, non-pregnancy group, but the shorter time interval between treatment and pregnancy (≤ 2 years) appeared to increase the risk of disease progression.MeaningFor young women previously treated for DTC, disease progression might not be a concern for their future pregnancy plan, but it seems safer to wait an appropriate amount of time before pregnancy.