[Incidence of postpartum thyroiditis and study of possible associated factors]

Our objective was to evaluate the presence of postpartum thyroiditis (PPT) in a group of pregnant euthyroid women.

This study was prospective and descriptive in nature and was carried out over the course of three years in an urban Health District in Toledo, Spain. Information recorded included height and weight, tobacco use, previous consumption of oral contraceptives, and numbers of pregnancies and abortions prior to the current gestation. Levels of Thyroid Stimulating Hormone (TSH), free Thyroxin (FT4) and thyroid peroxidase antibodies (TPOAb) were determined during the first trimester and 3 and 6 months postpartum. A urine sample was collected for determination of iodine levels. Thyroid ultrasonography was performed on all pregnant subjects concurrently with analytical sample collection at 3 months of pregnancy and 3 months postpartum.

The sample contained 157 pregnant women, of whom 25 (15.9%) developed PPT. Of these, 44.0% were positive for TPO antibodies in the first trimester, compared to 4.5% of the subjects who did not develop PPT (P<.001). At the end of the first year, 5 (20%) were still afflicted with hypothyroidism. The complete study group of pregnant women displayed a median urinary iodine level of 135 microg/L. A minor BMI was found in the PPT subjects when compared with the rest of the study group (21.7 vs 24.5; P=.000). A greater frequency of PPT was found in Rh-negative women (33.3 vs 12.2%; P=.015).

The incidence of PPT exceeded that previously reported. We have only found a significant correlation between PPT and BMI and Rh factor. Based on the high incidence rate detected in our Health District, an active search for cases of PPT might be justified.