Impact of pregnancy on serum thyroglobulin and detection of recurrent disease shortly after delivery in thyroid cancer survivors.

Objective: Since pregnancy can stimulate thyroid growth, we examined the effect of pregnancy on recurrence and serum thyroglobulin (Tg) shortly after delivery in thyroid cancer survivors.

Design: Retrospective analysis of thyroid cancer survivors who became pregnant after completing initial therapy.

Main Outcome: 36 women (age 34 +/- 4 years) who became pregnant a median of 4.3 years after initial therapy for differentiated thyroid cancer were evaluated a median of 4 months after delivery. As part of their initial therapy, 23 women underwent total thyroidectomy with radioactive iodine remnant ablation (RRA), six had total thyroidectomy without RRA, and seven underwent lobectomy without RRA. Following total thyroidectomy with or without RRA, no evidence of recurrence was detected in the early postpartum period in women with negative prepregnancy ultrasound and either undetectable or low suppressed Tg levels. However, disease progression was documented as enlargement of a previously stable cervical lymph node in one of three patients and a marked rise in serum Tg without evidence of structural disease progression in a patient with previously stable distant metastases. When analyzed based on initial therapy, the mean suppressed Tg after delivery was not significantly different than the prepartum value. However, eight women had Tg values after delivery more than 20% higher than the baseline Tg before pregnancy (three with known disease, five with no clinical evidence of disease).

Conclusion: In thyroid cancer survivors, pregnancy is unlikely to cause clinically significant disease recurrence in the early postpartum period when structural imaging studies confirm the absence of residual disease but can occasionally be associated with progression of known metastatic lesions. Even though the serum Tg did not differ significantly before and after pregnancy, the long-term implications of minor rise in serum Tg seen in some individual patients cannot be assessed without longer studies in larger cohorts.