Background: Active surveillance (AS) has emerged as an established management strategy for patients with low-risk papillary thyroid microcarcinoma (PTMC). However, prior studies have suggested accelerated tumor growth during pregnancy, which raises concerns about the suitability of AS for reproductive-age patients. This study evaluates the longitudinal impact of pregnancy on tumor dynamics and validates the safety of AS management in this population. Methods: From February 2020 to October 2024, a single-institution prospective AS cohort enrolled 260 female patients diagnosed with low-risk PTMC. Eighteen female patients (21 pregnancy events) with complete series of ultrasound documentation underwent longitudinal analysis of changes in tumor size and growth velocity, with time-stratified comparisons before pregnancy, during pregnancy, and after delivery. Tumor doubling rate (TDR) was calculated to quantify tumor growth or shrinkage patterns across these periods. An increase in tumor size of 3 mm or more was defined as substantial enlargement. Results: Over a median follow-up of 59.0 (interquartile range 38.5, 72.0) months, tumor enlargement (>3 mm) was observed in 19.0% (4/21) of the PTMC cases by the last follow-up. During pregnancy, 76.2% (16/21) of tumors exhibited accelerated growth (TDR >0.5/year) or moderate growth (TDR 0.1-0.5/year), whereas postpartum stabilization (TDR -0.1 to 0.1/year) or regression (TDR <-0.1/year) occurred in 71.4% (15/21). The TDR peaked during pregnancy and decreased after delivery (0.39/year vs. -0.01/year, p = 0.006). Delayed surgery was required in only two patients and no instances of expanded surgical scope, T-stage progression, or tumor recurrence were observed. Conclusion: While pregnancy may transiently accelerate tumor growth in low-risk PTMC, most gestational changes are self-limited, with stabilization or regression commonly observed postpartum. AS remains a safe and effective strategy for reproductive-age patients, balancing oncologic safety with fertility preservation. Confirmatory studies incorporating extended follow-up and advanced imaging modalities are essential to further validate these findings and optimize clinical frameworks.

Keywords: active surveillance; controlled before-after study; papillary thyroid microcarcinoma; pregnancy; tumor growth.

背景： 积极监测（AS）已成为低风险乳头状甲状腺微小癌（PTMC）患者的一种成熟的管理策略。然而，先前的研究表明怀孕期间肿瘤生长速度加快，这引发了人们对这种监测方法在生育年龄女性中适用性的担忧。本研究评估了怀孕对肿瘤动态的长期影响，并验证了在这一人群中实施积极监测的安全性。方法： 从2020年2月到2024年10月，一个单一机构的前瞻性AS队列纳入了260名被诊断为低风险PTMC的女性患者。其中18名（共21次怀孕）有完整的超声文档记录的女性患者接受了纵向分析，研究者对比了怀孕前、怀孕期间以及产后肿瘤大小和生长速度的变化情况。计算出的肿瘤倍增率（TDR）用于量化这些时期内肿瘤增长或缩小的情况。3毫米及以上肿瘤体积增加被定义为显著增大。结果： 中位随访时间为59.0个月（四分位距 38.5，72.0），在最后一次随访时有19.0%（4/21）的PTMC病例出现肿瘤扩大 (>3 mm)。怀孕期间，76.2%（16/21）的肿瘤表现出加速生长（TDR >0.5/year）或中度增长（TDR 0.1-0.5/year），而产后稳定（TDR -0.1至0.1/year）或消退（TDR p = 0.006）。仅有两名患者需要延迟手术，并未观察到扩大手术范围、T分期进展或肿瘤复发的情况。结论： 尽管怀孕可能暂时加速低风险PTMC的生长，但大多数妊娠变化是自限性的，在产后通常表现为稳定或消退。积极监测仍然是在生育年龄女性中平衡癌症安全性和生育保护的有效方法。为进一步验证这些发现并优化临床框架，需要进行包含延长随访和高级影像学模式的确证研究。

关键词： 积极监测；对照前后观察研究；乳头状甲状腺微小癌；怀孕；肿瘤生长。