Prevalence and characteristics of post-partum thyroid dysfunction: results of a survey from Toronto, Canada.

In order to determine the prevalence of post-partum thyroid dysfunction in our region, 1,376 randomly selected mothers were enrolled immediately post-partum and followed prospectively over a 2 year period in a large single-center survey. Beginning at delivery, sequential clinical and laboratory assessments were conducted at 6-8 week intervals up to 1 year post-partum and a questionnaire was administered at 3 months post-partum. Among the 1,376 mothers who qualified for entry into this study, 495 (36%) completed at least 3 months follow-up and 300 (22%) completed at least 1 year of follow-up. Abnormalities in post-partum thyroid function (PTD) were detected in 82 of the 1,376 enrolled mothers for an overall minimum prevalence rate of 6.0%. Hyperthyroidism confirmed to be associated with a low 24h radioactive iodine thyroid uptake (RAIU), compatible with the post-partum painless thyroiditis syndrome (PPT) was documented in 44 (3.2% minimum prevalence of typical PPT) of which 39 (89%) had a typical biphasic (hyperthyroid to hypothyroid) PTD while 5 (11%) had only a hyperthyroid phase with a suppressed RAIU without a subsequent hypothyroid phase. Another 17 (1.2%) had transient hyperthyroidism likely due to PPT but were not confirmed by an RAIU test and did not evolve to a detectable hypothyroid phase; and, 17 mothers (1.2%) had hypothyroidism between 5-7 months post-partum without preceding hyperthyroidism, resulting in an overall minimum prevalence of 5.7% for all variants of PPT. Graves' hyperthyroidism occurred in 3 (0.2%) and toxic nodular goiter was present in 1 (0.07%).(ABSTRACT TRUNCATED AT 250 WORDS)