BACKGROUND: The prevalence of thyroid dysfunction in pregnancy and in the first postpartum year (postpartum thyroid dysfunction (PPTD)) in women with diabetes mellitus type 1 (DM1) is known to be higher than in the general population. To assess prevalence, incidence and risk factors in The Netherlands we performed a prospective cohort study. DESIGN: From 1994 to 1998, 126 women with DM1 from eight Dutch clinics were included. TSH, free thyroxine, free tri-iodothyronine and anti-thyroid peroxidase antibodies (TPO-ab) were measured pre-pregnancy, in the first and last trimester of pregnancy and at 1.5, 3, 6, 9 and 12 months after delivery. RESULTS: Eighty-two women completed the study. Thyroid dysfunction during pregnancy was observed in 22.5% (first trimester) and 18.4% (third trimester), and mostly consisted of subclinical hypothyroidism. Baseline characteristics of women with thyroid dysfunction in pregnancy did not differ from those without thyroid dysfunction. Overt PPTD was seen in 15.9%. Incidence of PPTD was 10%. Patients with PPTD were slightly older than those without PPTD and the prevalence of TPO-ab was higher in these women. CONCLUSION: In women with DM1 the prevalence of thyroid dysfunction during pregnancy and overt PPTD is 3-fold higher than in the general Dutch population. Risk factors are age and TPO-ab. Given the possible impact on psychomotor development of the offspring and on well-being of the mother these data suggest there is a case for screening (pre-)pregnant women with DM1 for TSH and TPO-ab.
PR Gallas, RP Stolk, K Bakker, E Endert, and WM Wiersinga
W. Croughs, H. K. A. Visser, M. G. Woldring, and A. Bakker
The kinetics of thyroxin metabolism in adult man has been studied extensively (1, 2). In children only the data of Haddad (3) on 17 euthyroid children between 3 and 9 years of age are available.
Thyroxin turnover studies were carried out in 19 children between 3 and 15 years of age: euthyroid control 5; pituitary insufficiency 4; hypothyroidism during treatment 2; off treatment for 2 months 1; adolescent goiter 3; obesity 3 and one 3 years old eumetabolic child who had an iodine goiter at birth. Fractional rate of turnover K, thyroxin degradation rate D and other data were calculated according to Sterling cs. (2). In part of the children the thyroid gland was blocked with propylthiouracil; in the others also the thyroxin secretion rate S was calculated according to Ingbar cs. (1).
Results: Values for D and S were in good agreement. Mean value for K in 5 normal
M. G. Woldring, H. K. A. Visser, A. Bakker, and W. Croughs
As evidently the currently used iodine tracer doses are rather large for internal administration to human subjects, special attention was paid to an in vitro laboratory thyroid test, the so called resin triiodothyronine (T3) uptake test. With this method the degree of saturation of blood plasma with thyroxine is measured indirectly by incubating the plasma with an Amberlite CG 50 type and triiodothyronine labeled with I131. After subsequent separation and washing of the resin, diagnostic conclusions can be drawn from the percentage of the labeled T3 that remains fixed to the resin. The resin acts as a substrate to bind the exogenous T3 that is not preferentially bound by the plasma.
A higher percentage T3 is bound to the resin in hyperthyroidism, because the binding sites in the plasma are relatively more saturated by stable endogenous thyroxine and so more T3 is available for uptake by the resin.