Prevalence and characteristics of postpartum thyroid dysfunction in Sao Paulo, Brazil

OBJECTIVE Postpartum thyroid dysfunction (PPTD) is an autoimmune disorder c haracterized by the development of transient hyperthyroidism and, more freq uently, hypothyroidism (or both) during the first six months of the puerper al period. A variable incidence has been reported in part because of differ ences in the number of women studied, the frequency of thyroid assessment p ostpartum, diagnostic criteria and methodology. The aim of this study was t o evaluate thyroid function, ultrasound images and titre of autoantibodies against thyroid antigens in a cohort of pregnant women who met the criteria of 'normal' thyroid gland structure on clinical examination and imaging an d normal thyroid function tests without a significantly positive anti-thyro id peroxidase (TPO) antibody titre (i.e. < 1.00 U/ml) in the first trimeste r. DESIGN AND PATIENTS Eight hundred nulliparous or multiparous (one to seven previous pregnancies) pregnant women (age 26.1 +/- 4.8 years, mean +/- SD), were submitted to clinical, laboratory and ultrasonographic examination in the first trimester of pregnancy. Among these forty-six patients were excl uded because of thyroid dysfunction, ultrasound structural abnormalities or a positive anti-TPO antibody titre (> 100 U/ml). A total number of 754 wom en were available for further studies in the postpartum period. A relativel y large number of these patients (386) were lost for follow-up either befor e or after delivery. MEASUREMENTS A cohort of 368 puerperal women was followed up regularly at 3 , 6, 12 and 24 months after delivery, with periodic thyroid function tests, random urine iodine measurements, assays for serum autoantibodies against thyroid antigens and imaging by ultrasound. RESULTS The provisional diagnosis of PPTD was established in 78 out of 368 who had positive anti-TPO levels and ultrasonographic thyroid structural ch anges. Twenty-nine of these patients had a transient rise of anti-TPO autoa ntibodies characterizing an autoimmune reaction. These autoantibodies level s progressively declined or became negative. Moreover none of these patient s had evidence for altered thyroid function during the 18-24 months of foll ow-up. The remaining 49 patients (13.3%) progressively developed thyroid fu nction abnormalities (mainly hypothyroidism) indicating the presence of thy roid gland changes due to PPTD. Further follow-up studies indicated that at 18-24 months, 42 patients had serum levels of anti-TPO-Ab that were more e levated, as compared with the first year values. Predictive factors found d uring pregnancy for developing PPTD were: (1) relatively low levels of anti -TPO, between 60 and 100 U/ml (odds ratio 3.1:1), and (2) ultrasonographic thyroid structural changes in the first trimester (odds ratio 6.4:1). CONCLUSIONS We conclude that the prevalence of postpartum thyroid dysfuncti on in our geographical area ranges from 6.7% to 13.3%, considering, respect ively, all pregnant women that were examined (n=754) or only the number of puerperal women actually followed-up (n=368). A transient form of thyroid a utoimmune reaction characterized by elevated serum levels of anti-TPO that progressively declined or disappeared was observed in 29 puerperal women. S onographic structural and echogenicity changes in the thyroid gland and bor derline positive anti-TPO levels (between 60 and 100 U/ml) during pregnancy were considered to be of predictive value for development of postpartum th yroid dysfunction.