Postpartum thyroiditis in women with hypothyroidism antedating pregnancy?

In women with hypothyroidism, levothyroxine (LT) requirements after deliver y are assumed to return to prepregnancy values. The occasional observation of discordances prompted this study. Forty-one women (31 receiving LT repla cement therapy and 10 receiving suppressive therapy for thyroid carcinoma) were followed during the first year after delivery. A control group of 31 n onpregnant women with hypothyroidism (n = 21) or thyroid carcinoma (n = 10) were also followed during a similar period. Twenty-three patients of 41 (5 6.1%) had discordant requirements at follow-up after delivery vs. 3 of 31 i n the control group (9.7%; P < 0.001). The patterns of discordance in the p ostdelivery group were hyperthyroidism in 12, increase in LT dose in 5, hyp er- and hypothyroidism in 5, and recurrence of Graves' disease in 1 women. Those in the control group were increase in LT dose, hyperthyroidism, and h ypo- and hyperthyroidism. The rate of patients with discordant prepregnancy -postpartum LT doses was higher in the noncarcinoma subgroup (61.7% vs. 20. 0%; P < 0.01), whereas in the control group, both subgroups displayed a sim ilar rate of discordance (9.5% vs. 10%; P = NS). In conclusion, this study documents that women with hypothyroidism antedating pregnancy display chang es in LT requirements in the first year after delivery that suggest postpar tum thyroiditis.