Early pregnancy thyroid hormone reference ranges in Chilean women: the influence of body mass index

Mosso, Lorena; Martínez, Alejandra; Rojas, Mónica Maldonado; Latorre, Gonzalo; Margozzini, Paula; Lyng, Trinidad; Carvajal, Jorge; Campusano, Claudia; Arteaga, Eugenio; Boucai, Laura

doi:10.1111/cen.13127

Cited by 25 publications

(23 citation statements)

References 43 publications

(56 reference statements)

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“…These findings question the clinical usefulness of stratified reference ranges and may favor the use of the pregnancy week-specific reference combined with clinical awareness of maternal characteristics that may affect thyroid function results, particularly in the evaluation of patients with borderline results. Most pronounced was the effect of maternal BMI with higher TSH and lower fT4 limits in obese women, which is compatible with other reports (36)(37)(38). The role of other maternal characteristics has been less consistently reported in the literature (39), and our findings are less clear.…”

Section: Reference Rangessupporting

confidence: 87%

Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

Andersen

Carlé

et al. 2019

Thyroid

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Background: Physiological changes in maternal thyroid function during pregnancy necessitate the use of pregnancy specific reference ranges. Dynamic changes in TSH within the first trimester of pregnancy have been reported, but more evidence is needed to substantiate the findings. The objective of this study was to estimate pregnancy weekspecific reference ranges for maternal TSH and free T4 (fT4) in early pregnancy. Methods: We consecutively recruited serum residues from blood samples collected as part of the prenatal screening in the North Denmark Region, 2011-2015. TSH, fT4, thyroid peroxidase antibodies (TPO-Ab) and thyroglobulin antibodies (Tg-Ab) were measured using an ADVIA Centaur XPT immunoassay. The reference cohort included 10,337 pregnant women who had no thyroid disease or other autoimmune diseases and were TPO-Ab and Tg-Ab negative. The main outcome measures were lower and upper reference limits (2.5 and 97.5 percentiles) for TSH and fT4 stratified by week of pregnancy. Results: Blood samples were drawn in pregnancy week 4-20 (median week 10), and 92% of the pregnancies ended with live birth. TSH varied considerably in the first trimester of pregnancy, and the levels were highest in early pregnancy (week 4-6: 0.6-3.7 mIU/l) followed by a gradual decline to lower levels in week 9-11 (0.1-2.8 mIU/l) and 12-14 (0.03-2.8 mIU/l). Maternal fT4 showed less variation (week 4-6: 12-20 pmol/l; week 9-11: 13-21 pmol/l; week 12-14: 13-20 pmol/l). Conclusions: The results corroborate dynamic week-specific changes in maternal TSH in early pregnancy. The use of uniform lower and upper reference range for TSH in early pregnancy may be too simple.

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Section: Reference Rangessupporting

confidence: 87%

Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

Andersen

Carlé

et al. 2019

Thyroid

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“…It is possible that some determinants such as ethnic factors, environmental factors, or obesity as a comorbidity in our patients could have influenced the upper TSH reference value that we obtained [ 8 27 ].…”

Section: Discussionmentioning

confidence: 99%

Thyroid-Stimulating Hormone Reference Ranges in the First Trimester of Pregnancy in an Iodine-Sufficient Country

et al. 2018

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BackgroundThyroid dysfunction is associated with negative neonatal and obstetric outcomes. Large differences in thyroid function reference intervals exist across different populations. These differences can be explained by population-specific factors, such as iodine status. Many countries in Latin America report iodine sufficiency, but relatively few countries have published up-to-date data on iodine levels and thyroid function in the overall population, and especially in pregnant women. We evaluated the iodine status of pregnant women in Chile and determined thyroid hormone reference ranges in this population.MethodsThis was a prospective observational study of healthy Chilean women at their first prenatal visit before week 14. Thyroid-stimulating hormone (TSH), total thyroxine (T4), free T4, antithyroid peroxidase antibody (TPOAb), and iodine levels from spot urine samples were measured. Iodine status and the reference ranges for TSH were calculated.ResultsA total of 1,022 pregnant women in the first trimester were selected. Urinary iodine levels were measured in 302 randomly-selected women. The median urinary iodine concentration was 173.45 µg/L (interquartile range, 108.11 to 249.35).The reference ranges of TSH were calculated in 670 patients selected according to the National Academy of Clinical Biochemistry guidelines. The median TSH level was 1.88 µIU/mL (2.5th percentile: 0.13 to 97.5th percentile: 5.37). Using the reference range in the 1,022 women, the prevalence of clinical hypothyroidism was 1.76%, and that of subclinical hypothyroidism was 3.92%. TPOAb positivity was more common in women with TSH levels above 3.5 µIU/mL.ConclusionWe found adequate iodine intake and a right-shifted distribution of serum TSH levels in pregnant women in Chile. The prevalence of hypothyroidism in our sample of pregnant women was higher than has been described in the literature.

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“…In a study performed in Chile, BMI had a small but significant effect on TSH and FT4, which persisted after correction for maternal age, increased TPO-Abs, parity, gestational age, and smoking [30]. In a study in Finland, the upper limits for TSH in women with a BMI between 20 and 25 and with a BMI > 30 were 2.86 and 3.50 mU/L, respectively [31].…”

Section: Established Variables Contributing To Variation In Thyroid Fmentioning

confidence: 99%

Variables Contributing to Thyroid (Dys)Function in Pregnant Women: More than Thyroid Antibodies?

Veltri

Poppe

2018

Eur Thyroid J

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Variability in thyroid function in pregnant women is the result of 2 main determinants, each accounting for approximately half of it. The first is the genetically determined part of which the knowledge increases fast, but most remains to be discovered. The second determinant is caused by an ensemble of variables of which thyroid autoimmunity is the best known, but also by others such as parity, smoking, age, and BMI. More recently, new candidate variables have been proposed, such as iron, endocrine disruptors, and the ethnicity of the pregnant women. In the future, the diagnosis and treatment of thyroid (dys)function may be optimized by the use of each individual’s pituitary-thyroid set point, corrected with a factor taking into account the impact of nongenetically determined variables.

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Early pregnancy thyroid hormone reference ranges in Chilean women: the influence of body mass index

Cited by 25 publications

References 43 publications

Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

Thyroid-Stimulating Hormone Reference Ranges in the First Trimester of Pregnancy in an Iodine-Sufficient Country

Variables Contributing to Thyroid (Dys)Function in Pregnant Women: More than Thyroid Antibodies?

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