RESUMEN
OBJECTIVE: To assess iodine status and its effects on maternal thyroid function throughout pregnancy. DESIGN: In the present prospective cohort study, three urinary samples were requested for urinary iodine concentration (UIC) determinations in both the first and third gestational trimesters. Serum thyrotropin (TSH) and free thyroxine (FT4) were analysed in both trimesters and thyroid antibodies were assessed once. SETTING: Rio de Janeiro, Brazil.ParticipantsFirst-trimester pregnant women (n 243), of whom 100 were re-evaluated during the third trimester. RESULTS: Iodine sufficiency was found in the studied population (median UIC=216·7 µg/l). The first- and third-trimester median UIC was 221·0 and 208·0 µg/l, respectively. TSH levels (mean (sd)) were higher in the third trimester (1·08 (0·67) v. 1·67 (0·86) mIU/l; P<0·001), while FT4 levels decreased significantly (1·18 (0·16) v. 0·88 (0·12) ng/dl; P<0·001), regardless the presence of iodine deficiency (UIC<150 µg/l) or circulating thyroid antibodies. UIC correlated (ß; 95% CI) independently and negatively with age (-0·43; -0·71, -0·17) and positively with multiparity (0·15; 0·02, 0·28) and BMI (0·25; 0·00, 0·50). Furthermore, median UIC per pregnant woman tended to correlate positively with TSH (0·07; -0·01, 0·14). Women with median UIC≥250 µg/l and at least one sample ≥500 µg/l throughout pregnancy had a higher risk of subclinical hypothyroidism (OR=6·6; 95% CI 1·2, 37·4). CONCLUSIONS: In this cohort with adequate iodine status during pregnancy, excessive UIC was associated with an increased risk of subclinical hypothyroidism.
Asunto(s)
Hipotiroidismo/epidemiología , Yodo/orina , Adulto , Brasil/epidemiología , Femenino , Humanos , Embarazo , Estudios Prospectivos , Pruebas de Función de la Tiroides , Tirotropina/sangre , Tiroxina/sangreRESUMEN
OBJECTIVES: American Thyroid Association (ATA)'s new guidelines recommend use of population-based trimester-specific reference range (RR) for thyrotropin (TSH) in pregnancy. The aim of this study was to determine first trimester TSH RR for a population of pregnant women in Rio de Janeiro State. SUBJECTS AND METHODS: Two hundred and seventy pregnant women without thyroid illness, defined by National Academy of Clinical Biochemistry, and normal iodine status were included in this sectional study. This reference group (RG) had normal median urinary iodine concentration (UIC = 219 µg/L) and negative anti-thyroperoxidase antibodies (TPOAb). Twin pregnancy, trophoblastic disease and use of drugs or supplements that influence thyroid function were excluded. In a second step, we defined a more selective reference group (SRG, n = 170) by excluding patients with thyroiditis pattern on thyroid ultrasound and positive anti-thyroglobulin antibodies. This group also had normal median UIC. At a final step, a more selective reference group (MSRG, n = 130) was defined by excluding any pregnant women with UIC < 150 µg/L. RESULTS: In the RG, median, 2.5th and 97.5th percentiles of TSH were 1.3, 0.1, and 4.4 mIU/L, respectively. The mean age was 270 ± 5.0 and the mean body mass index was 25.6 ± 5.2 kg/m2. In the SRG and MSRG, 2.5th and 975th percentiles were 0.06 and 4.0 (SRG) and 0.1 and 3.6 mIU/L (MSRG), respectively. CONCLUSIONS: In the population studied,TSH upper limit in the first trimester of pregnancy was above 2.5 mIU/L. The value of 3.6 mIU/L, found when iodine deficiency and thyroiditis (defined by antibodies and ultrasound characteristics) were excluded, matches recent ATA guidelines.
Asunto(s)
Guías de Práctica Clínica como Asunto/normas , Primer Trimestre del Embarazo/sangre , Glándula Tiroides/diagnóstico por imagen , Tirotropina/sangre , Adulto , Autoanticuerpos/sangre , Autoantígenos/sangre , Brasil , Estudios Transversales , Femenino , Humanos , Yoduro Peroxidasa/sangre , Yodo/orina , Proteínas de Unión a Hierro/sangre , Embarazo , Valores de Referencia , Pruebas de Función de la Tiroides/normas , Tirotropina/normas , Ultrasonografía , Adulto JovenRESUMEN
ABSTRACT Objectives: American Thyroid Association (ATA)'s new guidelines recommend use of population-based trimester-specific reference range (RR) for thyrotropin (TSH) in pregnancy. The aim of this study was to determine first trimester TSH RR for a population of pregnant women in Rio de Janeiro State. Subjects and methods: Two hundred and seventy pregnant women without thyroid illness, defined by National Academy of Clinical Biochemistry, and normal iodine status were included in this sectional study. This reference group (RG) had normal median urinary iodine concentration (UIC = 219 μg/L) and negative anti-thyroperoxidase antibodies (TPOAb). Twin pregnancy, trophoblastic disease and use of drugs or supplements that influence thyroid function were excluded. In a second step, we defined a more selective reference group (SRG, n = 170) by excluding patients with thyroiditis pattern on thyroid ultrasound and positive anti-thyroglobulin antibodies. This group also had normal median UIC. At a final step, a more selective reference group (MSRG, n = 130) was defined by excluding any pregnant women with UIC < 150 μg/L. Results: In the RG, median, 2.5th and 97.5th percentiles of TSH were 1.3, 0.1, and 4.4 mIU/L, respectively. The mean age was 270 ± 5.0 and the mean body mass index was 25.6 ± 5.2 kg/m2. In the SRG and MSRG, 2.5th and 975th percentiles were 0.06 and 4.0 (SRG) and 0.1 and 3.6 mIU/L (MSRG), respectively. Conclusions: In the population studied,TSH upper limit in the first trimester of pregnancy was above 2.5 mIU/L. The value of 3.6 mIU/L, found when iodine deficiency and thyroiditis (defined by antibodies and ultrasound characteristics) were excluded, matches recent ATA guidelines.
Asunto(s)
Humanos , Femenino , Embarazo , Adulto , Adulto Joven , Primer Trimestre del Embarazo/sangre , Glándula Tiroides/diagnóstico por imagen , Tirotropina/sangre , Guías de Práctica Clínica como Asunto/normas , Valores de Referencia , Autoanticuerpos/sangre , Autoantígenos/sangre , Pruebas de Función de la Tiroides/normas , Brasil , Tirotropina/normas , Estudios Transversales , Ultrasonografía , Proteínas de Unión a Hierro/sangre , Yoduro Peroxidasa/orina , Yoduro Peroxidasa/sangreRESUMEN
OBJECTIVE: To evaluate iodine status among pregnant women from a coastal state after Brazilian governmental resolution reducing iodine concentrations in table salt. Secondarily, we correlated urinary iodine concentration (UIC) with thyroid volume and hormones. METHODS: Inductively coupled plasma mass spectrometry was used to assess UIC from 629 samples of 244 first trimester pregnant women. Thyroid ultrasound, serum thyroglobulin, thyrotropin, free thyroxine, and antithyroid antibodies were measured as iodine concentrations on samples of table salt from patient's home. RESULTS: Median UIC was adequate (221.0 µg/L); however, 48.7% of women had insufficient (<150 µg/L), and 4.5% excessive UIC (≥500 µg/L) in at least one sample. UIC was independently and negatively correlated with age (ß: -0.58; 95% confidence interval [CI], -0.89 to -0.27) and positively with multiparity (ß: 0.20; 95% CI, 0.04-0.34). In those without thyroiditis, UIC tended to be positively correlated with body mass index (P = 0.098) and thyrotropin (P = 0.072). Independent variables associated with iodine insufficiency were age >30 y (odds ratio [OR] = 2.0; 95% CI, 1.2-3.2) and obesity (OR = 0.2; 95% CI, 0.2-0.7). Excessive UIC was associated negatively with age (OR = 0.2; 95% CI, 0.04-0.8) and positively with multiparity (OR = 2.5; 95% CI, 1.0-6.0) and subclinical hypothyroidism (OR = 5.6; 95% CI, 1.0-30.2). CONCLUSION: This population has iodine sufficiency, and supplementation should not be generally considered, based on the risk association between excessive UIC and subclinical hypothyroidism.