SUN-007 Elevated Levothyroxine Requirements Post-Partum as Initial Presentation of Placenta Accreta

Introduction: It is well known that estrogen plays an important role in thyroid regulation. We report an unusual case of post-partum placenta accreta causing pathologic estrogen secretion leading to increased levothyroxine (LT4) requirements and inability to lactate. Case: A 36-year-old woman with history of Hashimoto’s hypothyroidism presented post-partum day 11 after a normal vaginal delivery with inability to produce breast milk and mildly elevated TSH levels. Prior to her pregnancy, she required an equivalent dose of 142 mcg of LT4 supplementation daily, which increased appropriately to 171 mcg during pregnancy. After delivery, LT4 was decreased to 150mcg in anticipation of normalization of levothyroxine requirements to pre-pregnancy level. However, she had difficulty lactating and was found to have elevated prolactin, estradiol, and TSH levels. The following day, she presented to her obstetrician for persistent vaginal bleeding and was found to have placenta accreta requiring dilation and curettage (D&C). Her LT4 requirements eventually dropped to 125 mcg with decreasing beta-HCG and estrogen levels after successful D&C treatment. She was also then able to produce sufficient breast milk for lactation. Discussion: This case highlights the effect of estrogen on LT4 requirements during physiologic pregnancy and postpartum with placenta accreta. It is expected that hypothyroid patients have approximately 25-50% increased thyroid replacement requirements during pregnancy, which normalizes soon after delivery.(1) Estrogen increases thyroxine-binding globulin and lowers circulating free thyroxine(2,), which causes higher thyroid replacement requirements. Estrogen is also known to inhibit lactation. Our patient demonstrates that this holds true even in a pathologically high estrogen state from placenta accreta. Our case uniquely demonstrates a temporal association between estrogen levels and LT4 requirements in the post-partum hypothyroid patient. Patients with inappropriately high TSH levels after delivery should prompt investigation into pathologic causes of elevated estrogen-states, as levothyroxine requirements are expected to normalize immediately post-partum. References: 1. Bungard TJ, Hurlburt M. Management of hypothyroidism during pregnancy. CMAJ. 2007;176(8):1077-8. 2. Alexander EK, Marqusee E, Lawrence J, Jarolim P, Fischer GA, Larsen PR. Timing and magnitude of increases in levothyroxine requirements during pregnancy in women with hypothyroidism. N Engl J Med. 2004 Jul 15;351(3):241-9.