Cigarette smoking during pregnancy is associated with alterations in maternal and fetal thyroid function

Husband smoking is associated with Wife's thyrotropin abnormality: A population-based cohort study among Chinese reproductive-aged women

OBJECTIVES

To comprehensively assess the association of husband smoking with wives' thyrotropin abnormality.

METHODS

This population-based retrospective cohort study included 2 406 090 Chinese reproductive-aged women who had participated twice in the National Free Pre-pregnancy Checkups Project between 2010 and 2020. Multivariate-adjusted odds ratios and 95% confidence intervals for subnormal and supranormal thyrotropin were estimated according to the husband's smoking status.

RESULTS

Husband smoking at the first visit was associated with a 17% (15%-20%) and 26% (24%-28%) increased odds of subnormal thyrotropin and supranormal thyrotropin respectively compared to participants in neither-smoker group. In non-smoking participants with normal thyrotropin levels at the first visit, the corresponding increased risk of subnormal thyrotropin and supranormal thyrotropin at the second visit were 15% (12%-18%) and 19% (16%-21%) in contrast to participants without husband-smoking exposure. In non-smoking participants with abnormal thyrotropin levels at their first visit, husband smoking cessation was associated with 27% (17%-35%) and 36% (31%-40%) reduced odds of subnormal thyrotropin and supranormal thyrotropin at the second visit compared with the participants whose husband still smoking at the second visit.

CONCLUSION

Husband smoking was associated with wives' subnormal thyrotropin and supranormal thyrotropin, and cessation of husband smoking could reduce the odds of thyrotropin abnormality. Couple-focused smoking intervention should be developed to reduce the burden of asymptomatic thyroid disease in females.

Evaluating the progression to abnormal thyrotropin in euthyroid preconception women: a population-based study

BACKGROUND

Abnormal preconception thyrotropin levels were associated with fecundability and adverse fetomaternal outcomes, however, little is known regarding the natural change of serum thyrotropin in euthyroid preconception women. Thus, we performed a population-based study to evaluate the progression to abnormal thyrotropin in euthyroid preconception women.

METHODS

This retrospective cohort study used data from the National Free Prepregnancy Checkups Project (NFPCP) collected between 2010 and 2020. Female Han Chinese participants aged 20-49 years who had two repeated NFPCP participations with a time interval of 1.5-3.0 years, confirmed non-pregnant status within this duration, and normal thyrotropin levels during their first participation were included for the analysis of thyrotropin abnormalities during the second NFPCP examination. Data were analyzed between June 1 and October 1, 2023.

RESULTS

This study included 186,095 euthyroid women of reproductive age (mean ± SD, 26.72 ± 4.70 years) whose preconception thyrotropin levels were between 0.37 and 4.87 mIU/L. The median follow-up time was 2.13 (IQR, 1.85-2.54) years. A total of 8,497 (4.57%) women developed abnormal thyrotropin, including 4,118 (2.21%) subnormal thyrotropin and 4,379 (2.35%) supranormal thyrotropin. Compared with the reference group (thyrotropin 1.01-2.00 mIU/L), the lower baseline thyrotropin group had greater risk of developing subnormal thyrotropin, and the higher baseline thyrotropin group had greater risk of developing supranormal thyrotropin. Moreover, the restricted cubic spline analysis revealed a U-shaped dose-response association of baseline thyrotropin levels or thyrotropin multiples of the median (MOM) levels against risk of subnormal thyrotropin in the follow-up, and a J-shaped dose-response association against risk of supranormal thyrotropin levels in the follow-up. We further found that baseline thyrotropin outside of 1.43-1.93 mIU/L or baseline thyrotropin MOM outside 0.59-1.36 would hava a higher risk of developing of abnormal thyrotropin.

CONCLUSIONS

Both low and high baseline thyrotropin were associated with a significantly increased risk of developing abnormal thyrotropin outcomes. The optimal preconception baseline thyrotropin levels may be between 1.43 mIU/L and 1.93 mIU/L or baseline thyrotropin MoM between 0.59 and 1.36 to minimize progression toward abnormal thyrotropin after 1.5-3.0 years. These findings may help with counseling of preconception thyroid function monitoring.

Does prenatal exposure to multiple airborne and tap-water pollutants increase neonatal thyroid-stimulating hormone concentrations? Data from the Picardy region, France

OBJECTIVE

Systematic screening for congenital hypothyroidism by heel-stick sampling has revealed unexpected heterogeneity in the geographic distribution of newborn thyroid-stimulating hormone concentrations in Picardy, France. We explored a possible relationship with environmental pollutants.

METHODS

Zip code geolocation data from mothers of newborns without congenital hypothyroidism born in 2021 were linked to ecological data for a set of airborne (particulate matter with a diameter of 2.5 μm or less [PM2.5] or 10 μm or less [PM10]) and tap-water (nitrate and perchlorate ions and atrazine) pollutants. Statistical associations between mean exposure levels during the third trimester of pregnancy and Thyroid-stimulating hormone (TSH) concentrations in 6249 newborns (51 % male) were investigated using linear regression models.

RESULTS

Median neonatal TSH concentration (interquartile range, IQR) was 1.7 (1-2.8) mIU/L. An increase of one IQR in prenatal exposure to perchlorate ions (3.6 μg/L), nitrate ions (19.2 mg/L), PM2.5 (3.7 μg/m3) and PM10 (3.4 μg/m3), were associated with increases in TSH concentrations of 2.30 % (95 % CI: 0.95-3.66), 5.84 % (95 % CI: 2.81-8.87), 13.44 % (95 % CI: 9.65-17.28) and 6.26 % (95 % CI: 3.01-9.56), respectively.

CONCLUSIONS

Prenatal exposure to perchlorate and nitrate ions in tap water and to airborne PM over the third trimester of pregnancy was significantly associated with increased neonatal TSH concentrations.

The Effects of Maternal Smoking on Thyroid Function: Findings from Routine First-Trimester Sonographic Anomaly Screening

AIM

This study aimed to assess the effect of tobacco exposure on maternal thyroid function and investigate its relationship to subclinical hypothyroidism in pregnant women during the first trimester.

SUBJECTS AND METHOD

A comparison of maternal thyroid function was made on 45 smokers, who composed the study group, and 72 non-smokers, pregnant women, who constituted the control group. After determining smokers by questionnaire, carbon monoxide (CO) levels in the expiratory air of the participants in both groups were measured and recorded, and the smokers' exposure was objectively confirmed.

RESULTS

Smoking and non-smoking pregnant women were similar regarding body mass index (BMI). While the TSH and fT4 levels were respectively 1.48 mlU/L and 11.43 pmol/L in pregnant women who smoked, that ratio changed to 1.72 mlU/L and 11.17 pmol/L in the non-smokers' group. But the differences between the groups were not statistically significant (p=0.239, p=0.179). Even though the rate of subclinical hypothyroidism was 8.9% in the smoking group, it was approximately 19.4% in the non-smoker group; the difference was not statistically significant (p=0.187).

CONCLUSION

This study proved that there is no statistically significant difference between maternal serum TSH and fT4 levels and the rate of subclinical hypothyroidism in smokers during pregnancy in the first trimester.

Association between maternal thyroid function and risk of gestational hypertension and preeclampsia

OBJECTIVES

To investigate the influence of maternal level of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxine (FT4) one by one or in combination on incidence of gestational hypertension and preeclampsia.

METHODS

The study included pregnant women (n=107) hospitalized in the period from July 1, 2020 to October 10, 2021 at the Department of Pathology of Pregnancy of the University Clinic of Obstetrics and Gynecology, University Clinical Center Sarajevo (UCCS) (Bosnia and Herzegovina), due to hypertensive disorder in pregnancy without symptoms of impaired thyroid function. In all patients fulfilling inclusion criteria TSH, FT3, and FT4 using electrochemiluminescence immunoassay (ECLIA, Roche Diagnostics, Basel, Switzerland) were checked. There were two groups of patients: one with gestational hypertension (G1) and the other with preeclampsia (G2). The programs SPSS for Windows 25.0, SPSS Inc, Chicago, IL, USA and Microsoft Excel 11, Microsoft Corporation, Redmond, WA, USA were used for statistical analysis using nonparametric Mann-Whitney U test because the distribution of the data was not normal. The result was considered statistically significant if p<0.05.

RESULTS

Gestational age at delivery (G2 36.86 ± 3.79 vs. G1 38.94 ± 2.15; p=0.002) and birth weight (G2 2,841.36 ± 1,006.39 vs. G2 3,290.73 ± 745.6; p=0,032) were significantly different between the investigated groups. The difference between the peak systolic (p=0.002), peak diastolic blood pressure (p=0.007), TSH (p=0.044), and FT3 (p=0.045) were statistically significant. Impaired thyroid function was observed more often in G2 than in G1.

CONCLUSIONS

Thyroid function was more often affected adversely in pregnancies complicated with preeclampsia than with gestational hypertension. Based on the results of our study it might be prudent to check thyroid hormones in all asymptomatic pregnancies with preeclampsia or gestational hypertension. These findings need confirmation in larger better designed prospective studies.

Prenatal exposure to organophosphate esters and neonatal thyroid-stimulating hormone levels: A birth cohort study in Wuhan, China

BACKGROUND

Increasing animal studies have indicated that organophosphate esters (OPEs) have endocrine-disruptive potential. However, human epidemiological evidence is limited, especially in susceptible populations, such as pregnant women and neonates. The purpose of this present study was to examine the trimester-specific relationships of prenatal exposure to OPEs with neonatal thyroid-stimulating hormone (TSH).

METHOD

A total of 102 mother-newborn pairs were recruited from a birth cohort study between April 2015 and September 2016 in Wuhan, China. Eight OPE metabolites were detectable in urine samples from pregnant women across the different three trimesters. Neonatal TSH levels were measured using time-resolved immunofluorescence assay. The associations between maternal urinary OPE metabolites and neonatal TSH and the critical exposure windows of fetal vulnerability were estimated using multiple informant models.

RESULTS

Seven OPE metabolites with detection frequency > 50% (52.9%-98.0%) were detected in repeated urine samples from different three trimesters, and the urinary OPE metabolites across pregnancy was of high variability (ICCs: 0.09-0.26). After adjusted for confounders (e.g., maternal age, prepregnancy BMI, passive smoking during pregnancy), some suggestive associations were observed between maternal urinary OPE metabolites and neonatal TSH in different trimesters. A doubling of second trimester di-o-cresyl phosphate & di-p-cresyl phosphate (DoCP & DpCP) was associated with a 7.82% increase in neonatal TSH level (95% CI: -0.70%, 17.06%, p-value = 0.07), a doubling of third trimester diphenyl phosphate (DPHP) was associated with a 4.71% decrease in neonatal TSH level (95% CI: -9.80%, 0.67%, p-value = 0.09), and a doubling of third trimester bis(2-butoxyethyl) phosphate (BBOEP) was associated with a 6.38% increase in neonatal TSH level (95% CI: -0.12%, 13.31%, p = 0.05). However, such associations did not differ materially across trimesters. When performing stratified analysis by infant sex, the associations were statistically significant and were sex-dependent.In females, maternal urinary DoCP & DpCP concentrations in each trimester were associated with increased neonatal TSH levels, and urinary DPHP concentration in the third trimester was associated with decreased neonatal TSH level. In males, maternal urinary BBOEP concentration in the first trimester was positively related to neonatal TSH level.

CONCLUSION

This prospective study demonstrated that prenatal exposure to OPEs can lead to a sex-dependent change in neonatal TSH levels. Although the sex-selective effect was differed among various urinary OPE metabolites, more evidence was supported that OPE exposure was related to increased TSH levels for both males and females.

Maternal adiposity, smoking, and thyroid function in early pregnancy

OBJECTIVE

A high activity of the deiodinase type 2 has been proposed in overweight, obese, and smoking pregnant women as reflected by a high triiodothyronine (T3)/thyroxine (T4) ratio. We speculated how maternal adiposity and smoking would associate with different thyroid function tests in the early pregnancy.

DESIGN

Cross-sectional study within the North Denmark Region Pregnancy Cohort.

METHODS

Maternal thyroid-stimulating hormone (TSH), total T4 (TT4), total T3 (TT3), free T4 (fT4), and free T3 (fT3) were measured in stored blood samples (median gestational week 10) by an automatic immunoassay. Results were linked to nationwide registers, and live-birth pregnancies were included. The associations between maternal adiposity (overweight or obese), smoking, and log-transformed TSH, fT3/fT4 ratio, and TT3/TT4 ratio were assessed using multivariate linear regression and reported as adjusted exponentiated β coefficient (aβ) with 95% CI. The adjusted model included maternal age, parity, origin, week of blood sampling, and diabetes.

RESULTS

Altogether 5529 pregnant women were included, and 40% were classified with adiposity, whereas 10% were smoking. Maternal adiposity was associated with higher TSH (aβ 1.13 (95% CI 1.08-1.20)), whereas maternal smoking was associated with lower TSH in the early pregnancy (0.875 (0.806-0.950)). Considering the T3/T4 ratio, both maternal adiposity (fT3/fT4 ratio: 1.06 (1.05-1.07); TT3/TT4 ratio: 1.07 (1.06-1.08)) and smoking (fT3/fT4 ratio: 1.07 (1.06-1.09); TT3/TT4 ratio: 1.10 (1.09-1.12)) were associated with a higher ratio.

CONCLUSIONS

In a large cohort of Danish pregnant women, adiposity and smoking showed opposite associations with maternal TSH. On the other hand, both conditions were associated with a higher T3/T4 ratio in early pregnancy, which may reflect altered deiodinase activity.

Maternal health, in-utero, and perinatal exposures and risk of thyroid cancer in offspring: a Nordic population-based nested case-control study

BACKGROUND

Thyroid cancer tends to be diagnosed at a younger age (median age 51 years) compared with most other malignancies (such as breast cancer [62 years] or lung cancer [71 years]). The incidence of thyroid cancer is higher in women than men diagnosed from early adolescence. However, few in-utero and early life risk exposures associated with increased risk of thyroid cancer have been identified.

METHODS

In this population-based nested case-control study we used registry data from four Nordic countries to assess thyroid cancer risk in offspring in relation to maternal medical history, pregnancy complications, and birth characteristics. Patient with thyroid cancer (cases) were individuals born and subsequently diagnosed with first primary thyroid cancer from 1973 to 2013 in Denmark, 1987 to 2014 in Finland, 1967 to 2015 in Norway, or 1973 to 2014 in Sweden. Each case was matched with up to ten individuals without thyroid cancer (controls) based on birth year, sex, country, and county of birth. Cases and matched controls with a previous diagnosis of any cancer, other than non-melanoma skin cancer, at the time of thyroid cancer diagnosis were excluded. Cases and matched controls had to reside in the country of birth at the time of thyroid cancer diagnosis. Conditional logistic regression models were used to calculate odds ratios (ORs) with 95% CIs.

RESULTS

Of the 2437 cases, 1967 (81·4%) had papillary carcinomas, 1880 (77·1%) were women, and 1384 (56·7%) were diagnosed before age 30 years (range 0-48). Higher birth weight (OR per kg 1·14 [95% CI 1·05-1·23]) and congenital hypothyroidism (4·55 [1·58-13·08]); maternal diabetes before pregnancy (OR 1·69 [0·98-2·93]) and postpartum haemorrhage (OR 1·28 [1·06-1·55]); and (from registry data in Denmark) maternal hypothyroidism (18·12 [10·52-31·20]), hyperthyroidism (11·91 [6·77-20·94]), goiter (67·36 [39·89-113·76]), and benign thyroid neoplasms (22·50 [6·93-73·06]) were each associated with an increased risk of thyroid cancer in offspring.

INTERPRETATION

In-utero exposures, particularly those related to maternal thyroid disorders, might have a long-term influence on thyroid cancer risk in offspring.

FUNDING

Intramural Research Program of the National Cancer Institute (National Institutes of Health).

Characterization of Fetal Thyroid Levels at Delivery among Appalachian Infants

Thyroid disorders are a frequently encountered issue during pregnancy and a cause of maternal and fetal morbidity. In regions like Appalachia that are particularly susceptible to health disparities, descriptive studies are needed to assist in identifying pathologic derangements. We sought to characterize fetal thyroid hormone levels at delivery and investigate whether or not maternal demographic characteristics affect the prevalence of neonatal thyroid disease. A cross-sectional analysis was conducted on 130 pregnant women recruited from the Tri-State region, incorporating areas of Kentucky, Ohio, and West Virginia. Total triiodothyronine (T3) (p = 0.4799), free T3 (p = 0.6323), T3 uptake (p = 0.0926), total thyroxine (T4) (p = 0.8316), free T4 (p = 0.0566), and Thyroid stimulating hormone (TSH) (p = 0.8745) levels were comparable between urban and rural newborns. We found no effect of hypertension status or nicotine levels on fetal umbilical cord thyroid hormone levels. Maternal diabetic status was associated with lower T4 (p = 0.0099) and free T4 (p = 0.0025) levels. Cotinine affected levels of T4 (p = 0.0339). In regard to maternal Body Mass Index (BMI), there was an increase in total T3 as BMI increased (p = 0.0367) and no significant difference in free T3, T3 uptake, T4, free T4, or TSH. There was a negative correlation between TSH and 1 min Apgar scores (p = 0.0058). Lead and cadmium have been implicated to alter TSH levels, but no correlation was found in our study (r² = 0.0277). There were no differences in cord blood between urban (37.3 ± 10.3 fmol/ug DNA) and rural (70.5 ± 26.8 fmol/ug DNA) benzo(a)pyrene DNA adducts (p = 0.174). Thyroid disorders present a unique opportunity for the prevention of perinatal morbidity and mortality, since maternal treatment, as well as maternal demographic characteristics, can have direct fetal effects.

Hypothyroidism and isolated hypothyroxinemia in pregnancy, from physiology to the clinic

Many changes occur in the physiology of the maternal thyroid gland to maintain an adequate level of thyroid hormones (THs) at each stage of gestation during normal pregnancy, however, some factors can produce low levels of these hormones, which can alter the onset and progression of pregnancy. Deficiency of THs can be moderate or severe, and classified as overt or clinical hypothyroidism, subclinical hypothyroidism, and isolated hypothyroxinemia. Overt hypothyroidism has been reported in 0.3-1.9% and subclinical hypothyroidism in approximately 1.5-5% of pregnancies. With respect to isolated hypothyroxinemia, the frequency has been reported in approximately 1.3% of pregnant women, however it can be as high as 25.4%. Worldwide, iodine deficiency is the most common cause of hypothyroidism, however, in iodine-sufficient countries like the United States, the most common cause is autoimmune thyroiditis or Hashimoto's thyroiditis. The diagnosis and timely treatment of deficiency of THs (before or during the first weeks of gestation) can significantly reduce some of the related adverse effects, such as recurrent pregnancy loss, preterm delivery, gestational hypertension, and alterations in the offspring. However, so far there is no consensus on the reference levels of thyroid hormones during pregnancy to establish the diagnosis and there is no consensus on universal screening of women during first trimester of pregnancy to identify thyroid dysfunction, to give treatment and to reduce adverse perinatal events, so it is necessary to carry out specific studies for each population that provide information about it.

Screening for Thyroid Dysfunction in Pregnancy With Targeted High-Risk Case Finding: Can It Be Improved?

CONTEXT AND OBJECTIVE

Targeted screening is proposed for the detection of thyroid dysfunction in pregnant women rather than universal screening (US). We aimed to determine the detection rate of subclinical hypothyroidism (SCH) and overt hypothyroidism (OH) based on American Thyroid Association guidelines (ATA-GL) and whether it could be improved.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional study of 1832 pregnant women in a single center. Thyroid function (TSH and free T4) and iron status were determined. The high-risk group (HRG) included women with one or more ATA-GL risk factors and the low-risk group (LRG) included women without. Participants with other risk factors [body mass index (BMI) 30 to 39.9 kg/m2, Caucasian background] were classified as HRG+ and those with iron deficiency as HRG++.

RESULTS

The HRG included 64% of women and the LRG included 36% (P < 0.001). Of all participants, 4.5% had SCH and 0.5% OH. The detection rate of SCH and OH was comparable between the LRG and HRG (46% vs 54% and 25% vs 75%; P = 0.560 and 0.157, respectively). In the HRG, the detection rate of SCH was lower than that of US (54% vs 100%; P < 0.001), but that of OH was comparable (75%; P = 0.596). The detection rate of SCH in the HRG+ and HRG++ was comparable to that in the US group (81% and 88% vs 100%; P = 0.220 and 0.439, respectively).

CONCLUSIONS

Targeted high-risk case finding screening was not effective for the detection of SCH but performed better for OH. When obesity in the range BMI 30 to 39.9 kg/m2 and a Caucasian background were included as risk factors, the detection rate of SCH became comparable with that of US.

Associations between Maternal Tobacco Smoke Exposure and the Cord Blood [Formula: see text] DNA Methylome

BACKGROUND

Maternal tobacco smoke exposure has been associated with altered DNA methylation. However, previous studies largely used methylation arrays, which cover a small fraction of CpGs, and focused on whole cord blood.

OBJECTIVES

The current study examined the impact of in utero exposure to maternal tobacco smoke on the cord blood [Formula: see text] DNA methylome.

METHODS

The methylomes of 20 Hispanic white newborns ([Formula: see text] exposed to any maternal tobacco smoke in pregnancy; [Formula: see text] unexposed) from the Maternal and Child Health Study (MACHS) were profiled by whole-genome bisulfite sequencing (median coverage: [Formula: see text]). Statistical analyses were conducted using the Regression Analysis of Differential Methylation (RADMeth) program because it performs well on low-coverage data (minimizes false positives and negatives).

RESULTS

We found that 10,381 CpGs were differentially methylated by tobacco smoke exposure [neighbor-adjusted p-values that are additionally corrected for multiple testing based on the Benjamini-Hochberg method for controlling the false discovery rate (FDR) [Formula: see text]]. From these CpGs, RADMeth identified 557 differentially methylated regions (DMRs) that were overrepresented ([Formula: see text]) in important regulatory regions, including enhancers. Of nine DMRs that could be queried in a reduced representation bisulfite sequencing (RRBS) study of adult [Formula: see text] cells ([Formula: see text] smokers; [Formula: see text] nonsmokers), four replicated ([Formula: see text]). Additionally, a CpG in the promoter of SLC7A8 (percent methylation difference: [Formula: see text] comparing exposed to unexposed) replicated ([Formula: see text]) in an EPIC (Illumina) array study of cord blood [Formula: see text] cells ([Formula: see text] exposed to sustained maternal tobacco smoke; [Formula: see text] unexposed) and in a study of adult [Formula: see text] cells across two platforms (EPIC: [Formula: see text] smokers; [Formula: see text] nonsmokers; 450K: [Formula: see text] smokers; [Formula: see text] nonsmokers).

CONCLUSIONS

Maternal tobacco smoke exposure in pregnancy is associated with cord blood [Formula: see text] DNA methylation in key regulatory regions, including enhancers. While we used a method that performs well on low-coverage data, we cannot exclude the possibility that some results may be false positives. However, we identified a differentially methylated CpG in amino acid transporter SLC7A8 that is highly reproducible, which may be sensitive to cigarette smoke in both cord blood and adult [Formula: see text] cells. https://doi.org/10.1289/EHP3398.

Thyroid Function Reference Values in Healthy Iodine-Sufficient Pregnant Women and Influence of Thyroid Nodules on Thyrotropin and Free Thyroxine Values

BACKGROUND

Thyroid function assessment in pregnancy requires specific reference intervals stratified by gestational age and according to each laboratory method. Thyroid nodules may influence thyroid function in pregnant women. The aims of this study were to define the reference values of thyrotropin (TSH) and free thyroxine (fT4) in the three pregnancy trimesters in iodine-sufficient pregnant women, and to analyze the influence of thyroid nodules on thyroid function during pregnancy.

METHODS

This was a prospective, longitudinal study comprising 400 pregnant women with no history of thyroid disease and no medication influencing thyroid function. TSH, fT4, antithyroglobulin, and antithyroid peroxidase antibodies were measured each trimester by chemiluminescent immunoassays. Urinary iodine concentration was measured in the first trimester when a thyroid echography was also performed. Women with multiple gestation pregnancies, positive thyroid autoimmunity, TSH values >5 or <0.1 mIU/L with a simultaneous fT4 level above the general population reference value in the first trimester, or clinically significant thyroid nodules (nodules ≥1 cm and/or multiple nodules) were excluded to establish TSH and fT4 reference values.

RESULTS

Reference intervals in the first, second, and third trimesters were 0.13-4.16, 0.31-3.73, and 0.58-4.36 mIU/L, respectively, for TSH, and 0.85-1.24, 0.82-1.20, and 0.67-1.06 ng/dL, respectively, for fT4. The total prevalence of thyroid nodules was 28.8% [95% confidence interval (CI) 24.4-33.5%], and 6.0% of the participants showed clinically significant nodules. Pregnant women with thyroid nodules (n = 115) showed consistently lower TSH values during all pregnancy stages (first trimester: median 1.14 mIU/L [interquartile range (IQR) 0.53-1.75 mIU/L] vs. 1.48 mIU/L [IQR 0.94-2.19 mIU/L], p < 0.001; second trimester: 1.22 mIU/L [IQR 0.66-1.77 mIU/L] vs. 1.45 mIU/L [1.04-2.05 mIU/L], p = 0.001; third trimester: 1.74 mIU/L [IQR 1.08-2.36 mIU/L] vs. 1.93 mIU/L [IQR 1.37-2.58 mIU/L], p = 0.041) and higher fT4 values in the first trimester (M ± SD = 1.08 ± 0.14 ng/dL vs. 1.03 ± 0.12, p < 0.001) compared to those without nodules (n = 285). Both pregnant women with clinically significant thyroid nodules and those with nonsignificant ones had lower TSH values than women without nodules.

CONCLUSIONS

TSH/fT4 reference intervals in pregnant women from the authors' geographical area will thyroid dysfunction in pregnancy to be appropriately diagnosed. The prevalence of thyroid nodules is high in iodine-sufficient pregnant women, and is associated with low TSH values across pregnancy.

Maternal smoking and high BMI disrupt thyroid gland development

BACKGROUND

Maternal lifestyle factors, including smoking and increased body weight, increase risks of adult diseases such as metabolic syndrome and infertility. The fetal thyroid gland is essential for the control of fetal metabolic rate, cardiac output, and brain development. Altered fetal thyroid function may contribute to increased disease onset later in life. Here, we investigated the impact of maternal smoking and high maternal weight on human fetal thyroid function during the second trimester.

METHODS

Thyroid glands and plasma were collected from fetuses electively terminated in the second trimester (normally progressing pregnancies). Plasma total triiodothyronine (T3) and total thyroxine (T4) were measured by solid-phase extraction-liquid chromatography-tandem mass spectrometry. Fetal plasma thyroid-stimulating hormone (TSH) levels were measured using a multiplex assay for human pituitary hormones. Histology and immunolocalization of thyroid developmental markers were examined in thyroid sections. Transcript levels of developmental, functional, apoptotic, and detoxification markers were measured by real-time PCR. Statistical analyses were performed using multivariate linear regression models with fetal age, sex, and maternal smoking or maternal body mass index (BMI) as covariates.

RESULTS

Maternal smoking was associated with significant changes in fetal plasma T4 and TSH levels during the second trimester. Smoke-exposed thyroids had reduced thyroid GATA6 and NKX2-1 transcript levels and altered developmental trajectories for ESR2 and AHR transcript levels. Maternal BMI > 25 was associated with increased fetal thyroid weight, increased plasma TSH levels, and abnormal thyroid histology in female fetuses. Normal developmental changes in AHR and ESR1 transcript expression were also abolished in fetal thyroids from mothers with BMI > 25.

CONCLUSIONS

For the first time, we show that maternal smoking and high maternal BMI are associated with disturbed fetal thyroid gland development and endocrine function in a sex-specific manner during the second trimester. These findings suggest that predisposition to post-natal disease is mediated, in part, by altered fetal thyroid gland development.

Association of Prenatal Exposure to Ambient and Traffic-Related Air Pollution With Newborn Thyroid Function: Findings From the Children's Health Study

IMPORTANCE

Thyroid hormones are critical for fetal growth and development. Prenatal particulate matter (PM) air pollution exposure has been associated with altered newborn thyroid function, but other air pollutants have not been evaluated, and critical windows of exposure are unknown.

OBJECTIVES

To investigate the association of prenatal exposure to ambient and traffic-related air pollutants with newborn thyroid function and identify critical windows of exposure.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used data from 2050 participants in the Children's Health Study. Statistical analyses were conducted from 2017 to 2018 using pregnancy and birth data from 1994 to 1997 for a subset of participants recruited from schools in 13 southern California communities in 2002 to 2003 when participants were 5 to 7 years of age. Participants were included in statistical analyses if they could be linked to their newborn blood spot and had complete monthly exposure measures for at least 1 air pollutant across pregnancy.

EXPOSURES

Prenatal monthly averages of ambient (PM diameter <2.5 μm [PM2.5] or <10 μm [PM10], nitrogen dioxide, and ozone) and traffic-related (freeway, nonfreeway, and total nitrogen oxides) air pollutant exposures were determined using inverse distance-squared weighting of central monitoring data and the California Line Source Dispersion model, respectively.

MAIN OUTCOMES AND MEASURES

Newborn heel-stick blood spot total thyroxine (TT4) measures were acquired retrospectively from the California Department of Public Health.

RESULTS

Participants included 2050 newborns (50.5% male), with a median (interquartile range) age of 20 (15-29) hours. The majority of newborns were Hispanic white (1202 [58.6%]) or non-Hispanic white (638 [31.1%]). Sixty-six (3.2%) were black and 144 (7.0%) were from other racial/ethnic groups. The mean (SD) newborn TT4 measure was 16.2 (4.3) μg/dL. A 2-SD increase in prenatal PM2.5 (16.3 μg/m3) and PM10 (22.2 μg/m3) was associated with a 1.2-μg/dL (95% CI, 0.5-1.8 μg/dL) and 1.5-μg/dL (95% CI, 0.9-2.1 μg/dL) higher TT4 measure, respectively, in covariate-adjusted linear regression models. Other pollutants were not consistently associated with newborn TT4. Distributed lag models revealed that PM2.5 exposure during months 3 to 7 of pregnancy and PM10 exposure during months 1 to 8 of pregnancy were associated with significantly higher newborn TT4 concentrations (P < .05).

CONCLUSIONS AND RELEVANCE

Prenatal PM exposure, particularly in early pregnancy and midpregnancy, is associated with higher newborn TT4 concentrations. Future studies should assess the health implications of PM-associated differences in newborn TT4 concentrations.

Reference Ranges and Determinants of Thyroid Function During Early Pregnancy: The SELMA Study

CONTEXT

Establishing reference ranges as well as identifying and quantifying the determinants of thyroid function during pregnancy is important for proper clinical interpretation and optimizing research efforts. However, such data are sparse, specifically for triiodothyronine measurements, and most studies do not take into account thyroid antibodies or human chorionic gonadotropin.

OBJECTIVE

To determine reference ranges and to identify/quantify determinants of TSH, free T4 (FT4), free triiodothyronine (FT3), total T4 (TT4), and total triiodothyronine (TT3).

DESIGN, SETTING, AND PARTICIPANTS

This study included 2314 participants of the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy study, a population-based prospective pregnancy cohort of mother-child pairs. Reference ranges were calculated by 2.5th to 97.5th percentiles after excluding thyroperoxidase antibody (TPOAb)-positive and/or thyroglobulin antibody (TgAb)-positive women.

INTERVENTION

None.

MAIN OUTCOME MEASURES

TSH, FT4, FT3, TT4, and TT3 in prenatal serum.

RESULTS

After exclusion of TPOAb-positive women, reference ranges were as follows: TSH, 0.11 to 3.48 mU/L; FT4, 11.6 to 19.4 pmol/L; FT3, 3.72 to 5.92 pg/mL; TT4, 82.4 to 166.2 pmol/L; and TT3, 1.28 to 2.92 nmol/L. Additional exclusion of TgAb-positive women did not change the reference ranges substantially. Exposure to tobacco smoke, as assessed by questionnaires and serum cotinine, was associated with lower TSH and higher FT3 and TT3. Body mass index (BMI) and gestational age were the main determinants of TSH (only for BMI), FT4, FT3, TT4, and TT3.

CONCLUSIONS

We show that the exclusion of TgAb-positive women on top of excluding TPOAb-positive women hardly affects clinical reference ranges. We identified various relevant clinical determinants of TSH, FT4, FT3, TT4, and TT3 that could reflect endocrine-disrupting effects and/or effects on thyroid hormone transport or deiodination.

MECHANISMS IN ENDOCRINOLOGY: Maternal thyroid dysfunction during pregnancy and behavioural and psychiatric disorders of children: a systematic review

BACKGROUND

Maternal thyroid dysfunction during pregnancy may lead to persistent neurodevelopmental disorders in the offspring appearing in later life. This study aimed to review the available evidence concerning the relationship between maternal thyroid status during pregnancy and offspring behavioural and psychiatric disorders.

METHODS

Systematic electronic database searches were conducted using PubMed, Embase, PsycNET, Scopus, Google Scholar and Cochrane library. Studies including gestational thyroid dysfunction as the exposure and offspring behavioural and psychiatric disorders as the outcome were included. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was followed and, after thorough screening by two independent reviewers, 13 articles remained eligible for inclusion in this study.

RESULTS

Indicators of maternal thyroid dysfunction, including low and high thyroid hormone level and autoimmune thyroiditis, during early pregnancy, were found to be associated with several offspring behavioural and psychiatric disorders such as attention deficit hyperactivity disorder (ADHD), autism, pervasive developmental problems, externalising behaviour, in addition to epilepsy and seizure. The majority of associations were found with low maternal thyroid hormone level.

CONCLUSION

Maternal thyroid function during pregnancy, particularly hypothyroidism, is associated with behavioural and psychiatric disorders in children. Further studies are needed with a capacity to adjust for a fuller range of confounding factors.

Iodine nutritional status of women in their first trimester of pregnancy in Catalonia

Background

Sufficient iodine intake is needed during pregnancy to ensure proper fetal development. The iodine levels of women in their first trimester of pregnancy in Catalonia are currently unknown. This data would help to determine whether our public health services should establish recommendations or interventions in this line. The aim of this study was to investigate the iodine nutritional status, prevalence of urinary iodine <150 μg/L, and tobacco use in the first trimester of pregnancy in our setting.

Methods

Cross-sectional study. Data were collected during 2008–2009 from women in their first trimester at the primary care centers of the province of Barcelona (Spain). Pregnant women included in the study completed a questionnaire on eating habits and underwent urinary iodine concentration (UIC) assessment.

Results

Nine hundred forty five women completed the dietary questionnaire and urinary iodine testing. Median UIC was 172 μg/L, with 407 participants (43.1%) showing levels <150 μg/L. On multivariate logistic regression analysis, intake of 1–2 glasses of milk per day, OR = 0.636 95% CI (0.45–0.90) or >2 glasses, OR = 0.593 95% CI (0.37–0.95); iodized salt consumption, OR = 0.678 95% CI (0.51–0. 90); and use of iodine supplementation, OR = 0.410 95% CI (0.31–0.54), protected against the risk of UIC <150 μg/L. Simultaneous consumption of iodized salt and milk (≥1 glass/day) showed a larger protective effect: OR = 0.427, 95% CI (0.31–0.54).

Conclusion

The median UIC of the pregnant women surveyed indicated an acceptable iodine nutritional status according to the criteria established by the WHO and ICCIDD. The risk of urinary iodine <150 μg/L decreased with simultaneous consumption of milk and iodized salt, similar to the decrease seen with iodine supplementation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12884-017-1423-4) contains supplementary material, which is available to authorized users.

Fetal Thyroid Function, Birth Weight, and in Utero Exposure to Fine Particle Air Pollution: A Birth Cohort Study

BACKGROUND

Thyroid hormones are critical for fetal development and growth. Whether prenatal exposure to fine particle air pollution (≤ 2.5 μm; PM_2.5) affects fetal thyroid function and what the impact is on birth weight in normal healthy pregnancies have not been studied yet.

OBJECTIVES

We studied the impact of third-trimester PM_2.5 exposure on fetal and maternal thyroid hormones and their mediating role on birth weight.

METHODS

We measured the levels of free thyroid hormones (FT₃, FT₄) and thyroid-stimulating hormone (TSH) in cord blood (n = 499) and maternal blood (n = 431) collected after delivery from mother-child pairs enrolled between February 2010 and June 2014 in the ENVIRONAGE birth cohort with catchment area in the province of Limburg, Belgium.

RESULTS

An interquartile range (IQR) increment (8.2 μg/m³) in third-trimester PM_2.5 exposure was inversely associated with cord blood TSH levels (-11.6%; 95% CI: -21.8, -0.1) and the FT₄/FT₃ ratio (-62.7%; 95% CI: -91.6, -33.8). A 10th-90th percentile decrease in cord blood FT₄ levels was associated with a 56 g decrease in mean birth weight (95% CI: -90, -23). Assuming causality, we estimated that cord blood FT₄ mediated 21% (-19 g; 95% CI: -37, -1) of the estimated effect of an IQR increment in third-trimester PM_2.5 exposure on birth weight. Third-trimester PM_2.5 exposure was inversely but not significantly associated with maternal blood FT₄ levels collected 1 day after delivery (-4.0%, 95% CI: -8.0, 0.2 for an IQR increment in third-trimester PM_2.5).

CONCLUSIONS

In our study population of normal healthy pregnancies, third-trimester exposure to PM_2.5 air pollution was associated with differences in fetal thyroid hormone levels that may contribute to reduced birth weight. Additional research is needed to confirm our findings in other populations and to evaluate potential consequences later in life.

The effect of smoking on placental pendrin expression

Pendrin is important for transport of iodine across the placenta. Thiocyanate coming from cigarette is a competitive inhibitor of iodine transport. We aimed to evaluate the pendrin immunostaining intensity in placentas of smoker and non-smoker women. Placental tissues from 61 women, of which 28 were in smoking, and 33 were in non-smoking group were evaluated by immunohistochemical staining. Positive immunostaining was evaluated using a semiquantitative score: 0, negative; +, mild; ++, moderate; and +++, intense. Birth weight was significantly lower in the smoker group (p = 0.024). There was a negative correlation between birth weight and intensity of placental pendrin immunostaining in the smoker group (r = -0.44, p = 0.02). Placentas of the smoking women showed significantly higher immunostaining with pendrin than the control group (p = 0.006). Thiocyonate coming from cigarettes may competitively inhibit pendrin mediated iodine transport in the placenta and adversely affect foetal development by this mechanism.

Thyroid Hormone Status in Umbilical Cord Serum Is Positively Associated with Male Anogenital Distance

CONTEXT

In human adults and adolescents, thyroid function affects sex hormones and male reproductive functions. Little is known about the thyroid function effects on the gonadal development in human infants.

OBJECTIVE

The aim was to examine the association between thyroid hormones (THs) and sexually dimorphic genital development or fetal growth.

DESIGN

This is a birth cohort study.

PARTICIPANTS

A total of 616 mothers and newborns were analyzed from two local hospitals.

MAIN OUTCOME MEASURES

TSH, free T3 (FT3), and free T4 (FT4) levels in cord blood serum, anogenital distance (AGD), birth weight, birth length, birth body mass index, and head circumference in neonates.

RESULTS

Longer AGD in male newborns was observed with higher cord serum FT3 (β, 1.36 mm [95% confidence interval (CI), 0.58-2.13] for 1 pmol/L FT3), FT4 (β, 0.12 mm [95% CI, 0.00-0.25] for 1 pmol/L FT4), and TSH (β, 3.14 mm [95% CI, 0.65-5.63] for a 10-fold TSH increase), and with a lower FT4/FT3 ratio (β, -0.11 mm [95% CI, -0.20 to -0.02] for doubling FT4/FT3 ratio). The relationships between TSH, birth weight, and birth length were different by secondhand smoke exposure. Secondhand smoke exposure had an effect modification, with interaction P value .039 and .010, respectively. Secondhand smoke exposure also had an effect modification on the relation between FT4 and head circumference with interaction P value .020.

CONCLUSIONS

In the absence of overt thyroid dysfunction, THs are positively associated with AGD in male newborns. TH effects on body size and head circumference may be modified by maternal secondhand smoke exposure.

Pregnancy Outcome in Euthyroid Women with Anti-Thyroid Peroxidase Antibodies

OBJECTIVE

The aim of this study was to compare pregnancy outcomes in euthyroid women who were anti-TPO Ab(+) with those who were anti-TPO Ab(-).

DESIGN

This observational study comprised 1,000 women in the age group of 25-35 years, having normal thyroid function tests, normotensive, non-diabetic, singleton pregnancy and attending Gyn. OPD/ANC up to 20 weeks' gestation and those who were already in the process of abortion. anti-TPO Ab levels of >50 IU/ml were considered as anti-TPO Ab(+).

SETTING

This study was conducted in the SMS Medical College's attached hospital, Jaipur from April 2012 to September 2013.

MAIN OUTCOME

The estimation of the proportion of anti-TPO Abs in the hospital-based population and the comparison of pregnancy and neonatal outcomes in anti-TPO Ab(+) and Ab(-) euthyroid women were done.

RESULTS

The main result showed increased rates in miscarriages (13.33 vs. 2.34 %, P < 0.001), LBWs (25 vs. 5.12 %, P < 0.001), preterm deliveries [<34 weeks] (5 vs. 1.80 %, P > 0.05) in anti-TPO Ab(+) women.

CONCLUSIONS

The current study revealed that anti-TPO Abs are strongly associated with miscarriage and LBW irrespective of their gestational age. However, we did not find any correlation with the other complication as found in the studies by Abbassi-Ghanavati, Negro et al.

Maternal hypothyroxinaemia in pregnancy is associated with obesity and adverse maternal metabolic parameters

OBJECTIVE

Subclinical hypothyroidism and isolated hypothyroxinaemia in pregnancy have been associated with an increased risk of gestational diabetes. We aimed to ascertain if these women have a worse metabolic phenotype than euthyroid pregnant women.

DESIGN, SUBJECTS AND METHODS

We recruited 956 healthy Caucasian women with singleton, non-diabetic pregnancies from routine antenatal clinics. Detailed anthropometric measurements (including BMI and skinfold thickness) and fasting blood samples (for TSH, free thyroxine (FT4), free triiodothyronine (FT3), HbA1c, lipid profile, plasma glucose and insulin resistance (HOMA-IR) analysis) were obtained at 28 weeks gestation.

RESULTS

In comparison to euthyroid women (n=741), women with isolated hypothyroxinaemia (n=82) had significantly increased BMI (29.5 vs 27.5 kg/m(2), P<0.001), sum of skinfolds (57.5 vs 51.3 mm, P=0.002), fasting plasma glucose (4.5 vs 4.3 mmol/l, P=0.01), triglycerides (2.3 vs 2.0 mmol/l, P<0.001) and HOMA-IR (2.0 vs 1.3, P=0.001). Metabolic parameters in women with subclinical hypothyroidism (n=133) were similar to those in euthyroid women. Maternal FT4 was negatively associated with BMI (r=-0.22), HbA1c (r=-0.14), triglycerides (r=-0.17), HOMA-IR (r=-0.15) but not total/HDL cholesterol ratio (r=-0.03). Maternal FT3:FT4 ratio was positively associated with BMI (r=0.4), HbA1c (r=0.21), triglycerides (r=0.2), HOMA-IR (r=0.33) and total/HDL cholesterol ratio (r=0.07). TSH was not associated with the metabolic parameters assessed.

CONCLUSIONS

Isolated hypothyroxinaemia, but not subclinical hypothyroidism, is associated with adverse metabolic phenotype in pregnancy, as is decreasing maternal FT4 and increasing FT3:FT4 ratio. These associations may be a reflection of changes in the thyroid hormone levels secondary to increase in BMI rather than changes in thyroid hormone levels affecting body weight and related metabolic parameters.

Thyroid Function in Pregnancy: What Is Normal?

BACKGROUND

Gestational thyroid dysfunction is common and associated with maternal and child morbidity and mortality. During pregnancy, profound changes in thyroid physiology occur, resulting in different thyroid-stimulating hormone (TSH) and free thyroxine (FT4) reference intervals compared to the nonpregnant state. Therefore, international guidelines recommend calculating trimester- and assay-specific reference intervals per center. If these reference intervals are unavailable, TSH reference intervals of 0.1–2.5 mU/L for the first trimester and 0.2–3.0 mU/L for the second trimester are recommended. In daily practice, most institutions do not calculate institution-specific reference intervals but rely on these fixed reference intervals for the diagnosis and treatment of thyroid disorders during pregnancy. However, the calculated reference intervals for several additional pregnancy cohorts have been published in the last few years and show substantial variation.

CONTENT

We provide a detailed overview of the available studies on thyroid function reference intervals during pregnancy, different factors that contribute to these reference intervals, and the maternal and child complications associated with only minor variations in thyroid function.

SUMMARY

There are large differences in thyroid function reference intervals between different populations of pregnant women. These differences can be explained by variations in assays as well as population-specific factors, such as ethnicity and body mass index. The importance of using correct reference intervals is underlined by the fact that even small subclinical variations in thyroid function have been associated with detrimental pregnancy outcomes, including low birth weight and pregnancy loss. It is therefore crucial that institutions do not rely on fixed universal cutoff concentrations, but calculate their own pregnancy-specific reference intervals.

Thyroid status and its association with cognitive functioning in healthy boys at 10 years of age

OBJECTIVE

Thyroid hormones (THs) are crucial for the correct maturation of the CNS and the neurodevelopment of the child. We aimed to investigate the association of TSH and free thyroxine (FT4) levels with cognitive functioning in children from the INMA-Granada cohort studied during their follow-up at the age of 9-11 years.

DESIGN

We evaluated 300 children from the original cohort, which comprised 668 eligible mother-son pairs recruited at birth from 2000 to 2002 in Granada (Spain).

METHODS

FT4 and TSH concentrations were measured, and cognitive development was assessed using neuropsychological tests (n=187). Children with chronic disease related to thyroid function and/or cognitive development were excluded.

RESULTS

Median TSH and FT4 levels were 3.1 μIU/ml and 1.2 ng/dl respectively. In multivariable regression analyses adjusted for maternal and child characteristics, children with TSH levels in the top tertile had worse verbal comprehension and immediate and long-term recall. Children with FT4 levels in the top tertile had better attention and lower impulsivity and were at a lower risk of scoring below the 20th percentile in intelligence quotient (OR=0.24; 95% CI=0.08-0.74; P=0.013) and in abstract reasoning ability (OR=0.28; 95% CI=0.09-0.88; P=0.029).

CONCLUSION

Our findings indicate that circulating THs and TSH may in the top tertile have an impact on cognitive functions; thus, higher TSH slightly but significantly increased the risk of a lower score in certain neuropsychological tests.

Thyroid disorders during pregnancy

Thyroid disorders are common in pregnancy and in nonpregnant women of childbearing age, but can be missed because of nonspecific symptoms and normal changes in thyroid gland physiology during pregnancy. The prevalence of overt hyperthyroidism complicating pregnancy has been reported to range between 0.4% and 1.7%, and an estimated 2% to 3% of women are hypothyroid during pregnancy. Abnormalities in maternal thyroid function are associated with complications during pregnancy, and may affect maternal and fetal outcomes. Thus it is important to identify thyroid disorders before pregnancy or early in pregnancy so that appropriate treatment can be initiated.

Effect of maternal nicotine/thiocyanate exposure during gestational period upon pituitary, thyroid and parathyroid function/morphology of 1-month-old rat offspring

INTRODUCTION

Impact of in utero exposure to nicotine, on the structure of the thyroid-pituitary axis and the parathyroid glands have been examined in 1-month-old rats and compared with that of thiocyanate.

MATERIALS AND METHODS

Three pregnant female groups were used; control, nicotine and thiocyanate. Treatment started from gestation day (4-20) and the specimens were harvested from the male offspring of all groups at the age of 1 month and processed for light, electronmicroscopic and immunohistochemical examination. Total triiodothyronine (tT3), total thyroxine (tT4) and total thyrotropin (TSH) were quantitatively determined in serum.

RESULTS

Both nicotine and thiocyanate activated the thyroid follicular cells, with an increase in height (about 30 %) and a negative feedback on the pituitary thyrotrophs which revealed a reduction in the number of cytoplasmic secretory granules, particularly the thiocyanate group. However, in thiocyanate group there was signs of impaired secretory activity of the thyroid gland. The arbitrary area of parathyroid chief cells, increased (about 45 %) particularly in nicotine group, with signs of reduced activity and a positive feedback on the parafollicular cells which revealed hypertrophy, proliferation (25 %) and increased intensity of positive immunohistochemical reaction for calcitonin.

CONCLUSION

Nicotine impaired chief parathyroid cells activity and consequently activated parafollicular cells. Thiocyanate reduced pituitary thyrotrophs activity, whereas both nicotine and thiocyanate increased thyroid follicular cells activity. This impact of in utero exposure persisted for 1-month postnatal.

Gestational age-specific reference ranges from different laboratories misclassify pregnant women's thyroid status: comparison of two longitudinal prospective cohort studies

OBJECTIVES

Correct interpretation of thyroid status during pregnancy is vital to secure fetal development. Pregnancy-related changes in maternal thyroid status necessitate the use of gestational age-specific reference ranges. In this study, we investigated between-laboratory reproducibility of thyroid reference ranges in pregnant women.

DESIGN

Comparison of two longitudinal prospective cohort studies including 255 (cohort 1) and 101 (cohort 2) healthy antibody-negative Danish pregnant women attending prenatal care at Copenhagen University Hospital.

METHODS

Different immunoassays were used to measure thyroid hormone levels in the two cohorts. Thyroid hormone reference ranges were established for every 5 weeks of gestation. Differences between cohorts were explored through mixed-model repeated measures regression analyses. By applying reference ranges from one cohort to the other, the proportion of women who would be misclassified by doing so was investigated.

RESULTS

TSH increased and free thyroxine (FT4) decreased as pregnancy progressed. Results indicated highly significant differences between cohorts in free triiodothyronine (F=21.3, P<0.001) and FT4 (F=941, P<0.001). TSH levels were comparable (P=0.09). Up to 90.3% of the women had FT4 levels outside their laboratory's nonpregnant reference range, and up to 100% outside the other cohort's gestational-age-specific reference ranges. Z-score-based reference ranges markedly improved comparison between cohorts.

CONCLUSION

Even in the same region, the use of gestational-age-specific reference ranges from different laboratories led to misclassification. Up to 100% of maternal FT4 levels fell outside the other cohort's reference range despite similar TSH levels. In clinical practice, thyroid testing of pregnant women without adding method specificity to gestational age-dependent reference ranges will compromise patient safety.

Smoking reduces the risk of hypothyroidism and increases the risk of hyperthyroidism: evidence from 450,842 mothers giving birth in Denmark

OBJECTIVE

Smoking may influence on the occurrence of thyroid disease, but studies have led to inconsistent results. In Denmark, information on maternal smoking during pregnancy is registered by midwives, and we investigated the association between maternal smoking as reported during pregnancy and the subsequent maternal risk of having hyper- or hypothyroidism diagnosed.

DESIGN

Population-based cohort study.

PARTICIPANTS

Using Danish nationwide registers, we identified mothers giving birth in Denmark, 1996-2008, and studied their first pregnancy in the study period.

MEASUREMENTS

Information on maternal smoking during the pregnancy and maternal diagnosis of hyper- or hypothyroidism was obtained from the Danish National Hospital Register (DNHR) and prescription of thyroid medication from the Danish National Prescription Register (DNPR). Cox proportional hazards model was used to estimate hazard ratio (HR) with 95% confidence interval (95% CI) for onset of maternal hyper- or hypothyroidism after birth of the child in multivariate analyses adjusting for potential confounders.

RESULTS

Among mothers included (n = 450 842), altogether 89,022 (19·7%) reported that they were smokers during the first pregnancy in the study period, and 8905 (2·0%) developed hyper (n = 3389)- or hypothyroidism (n = 5516) after birth of the child. Maternal smoking was associated with a subsequent decreased risk of developing hypothyroidism (adjusted HR 0·75 (95% CI 0·70-0·81)) and an increased risk of hyperthyroidism (1·38 (1·27-1·49)).

CONCLUSIONS

Danish nationwide registration of maternal smoking during pregnancy adds further evidence to an association between smoking and thyroid dysfunction; smoking reduced the risk of hypothyroidism and increased the risk of hyperthyroidism.

[Reference values and variability study of thyroid hormones in pregnant women from El Bierzo]

BACKGROUND AND OBJECTIVES

El Bierzo area is characterized by low urinary iodine levels in the pregnant population. Guidelines recommend that local reference values are established for the diagnosis of thyroid dysfunction in pregnancy. Our objectives were to establish reference values for thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) in women in the first trimester of pregnancy and to explore the factors influencing variability in these hormones.

PATIENTS AND METHODS

A retrospective study of 412 women in the first trimester of pregnancy who were measured serum levels of TSH, FT4, and FT3; 163 women with conditions with a potential influence on thyroid function were excluded. Thirty smoking pregnant women were also excluded from the study of reference values. Factors examined in the variability study included age, body mass index (BMI), and smoking. A multifactorial analysis of covariance was performed.

RESULTS

Reference values in first-trimester pregnant women were: TSH: 0.497-3.595 mIU/L; FT4: 0.90-1.42 ng/dL; FT3: 2.49-3.56 pg/mL. TSH levels depended on mother age and on interaction between age and smoking. FT3 levels depended on the mother's BMI and smoking, and there was also an interaction between both factors.

CONCLUSION

The reference values found may be used to assess thyroid dysfunction in pregnant women from El Bierzo. TSH and FT3 levels are influenced by age and BMI of the mother and by smoking, in addition to the interaction of these factors.

Endocrine effects of tobacco smoke exposure during lactation in weaned and adult male offspring

Children from pregnant smokers show more susceptibility to develop obesity in adult life. Previously, we failed to demonstrate a program for obesity in rat offspring only when the mothers were exposed to tobacco smoke during lactation. Here, we studied the short- and long-term effects of smoke exposure (SE) to both dams and their pups during lactation on endocrine and metabolic parameters. For this, we designed an experimental model where nursing rats and their pups were divided into two groups: SE group, exposed to smoke in a cigarette smoking machine (four times/day, from the third to the 21st day of lactation), and group, exposed to filtered air. Pups were killed at 21 and 180 days. At weaning, SE pups showed lower body weight (7%), length (5%), retroperitoneal fat mass (59%), visceral adipocyte area (60%), and higher subcutaneous adipocyte area (95%) with hypoinsulinemia (-29%), hyperthyroxinemia (59%), hypercorticosteronemia (60%), and higher adrenal catecholamine content (+58%). In adulthood, SE offspring showed higher food intake (+10%), body total fat mass (+50%), visceral fat mass (retroperitoneal: 55%; mesenteric: 67%; and epididymal: 55%), and lower subcutaneous adipocyte area (24%) with higher serum glucose (11%), leptin (85%), adiponectin (1.4-fold increase), total triiodothyronine (71%), free thyroxine (57%), TSH (36%), triglycerides (65%), VLDL cholesterol (+66%), and HDL cholesterol (91%) levels and lower corticosteronemia (41%) and adrenal catecholamine content (57%). Our present findings suggest that tobacco SE to both dams and their pups during lactation causes malnutrition in early life that programs for obesity and hormonal and metabolic disturbances in adulthood, only if the pups are submitted to the same smoke environment as the mother.

Relative impact of iodine supplementation and maternal smoking on cord blood thyroglobulin in pregnant women with normal thyroid function

OBJECTIVE

To assess the impact on cord blood (CB) thyroglobulin (Tg) of early iodine supplementation during pregnancy.

METHODS

A total of 111 healthy pregnant women with normal thyroid function were included in a prospective randomized study and divided into two groups with (150 μg/day) or without iodine supplementation started during the first trimester. Maternal smoking was assessed qualitatively by self-reported statements and quantitatively by cotininuria. Exhaustive thyroid tests were performed at delivery in the mother and in CB.

RESULTS

Third-trimester ioduria documented compliance with iodine supplementation (160 vs. 76 μg/l in controls). CB Tg was not different between the iodine and control groups (median 77 vs. 79.5 ng/ml, respectively) and did not correlate with maternal ioduria. CB Tg was higher in newborns from smoking mothers (114 vs. 64.7 ng/ml) and correlated with self-reported smoking status more than with maternal cotininuria. Nonsmokers had no difference in CB Tg whether they took iodine supplementation or not, as opposed to smokers, who tended to benefit from supplementation.

CONCLUSIONS

Iodine supplementation does not significantly impact CB Tg in healthy nonsmoker pregnant women selected for normal thyroid function, as opposed to maternal smoking. CB Tg appears to be a marker of in utero tobacco exposure. In areas of mild iodine deficiency, iodine supplementation could especially benefit the fetuses of smokers.

Iodine status has no impact on thyroid function in early healthy pregnancy

Aim. To assess the impact of iodine status in early pregnancy on thyroid function. Methods. Women >18 years old seen at their first prenatal consult before 12 weeks of amenorrhea and without personal thyroid history were proposed thyroid screening and were eligible if they had strictly normal thyroid tests (fT4 > 10th percentile, TSH < 2.5 mUI/L, negative anti-TPO antibodies). Evaluation included thyroid ultrasound, extensive thyroid tests, and ioduria (UIE). Results. 110 women (27.5 y, 8 weeks of amenorrhea, smoking status: 28% current smokers) were enrolled. Results are expressed as medians. UIE was 116 μg/L. 66.3% of women had iodine deficiency (ID) defined as UIE < 150. FT4 was 14.35 pmol/L; TSH 1.18 mUI/L; fT3 5 pmol/L; thyroglobulin 17.4 ng/mL; rT3 0.27 ng/mL; thyroid volume: 9.4 ml. UIE did not correlate with any thyroid tests, but correlated negatively with thyroid volume. UIE and all thyroid tests, except fT3, correlated strongly with βhCG. Smoking correlated with higher thyroid volume and thyroglobulin and with lower rT3. Conclusions. In pregnant women selected for normal thyroid function, mild ID is present in 66% during the 1st trimester. The absence of correlation between UIE and thyroid tests at that stage contrasts with the impact of βhCG and, to a lesser degree, maternal smoking.

Secondhand tobacco smoke exposure is associated with prolactin but not thyroid stimulating hormone among nonsmoking women seeking in vitro fertilization

Prolactin (PRL) and thyroid stimulating hormone (TSH) serve important roles in the reproductive and other systems. Active smoking is associated with changes in PRL and TSH secretion, but the relationship between secondhand tobacco smoke (STS) exposure and these hormones is unclear. We measured PRL and TSH in serum as well as cotinine in follicular fluid (to estimate STS exposure) among 314 nonsmoking women undergoing in vitro fertilization treatment. We observed a significant increase in PRL concentrations (p=0.03) among STS-exposed nonsmokers compared to unexposed nonsmokers. There was no significant difference in TSH concentration (p>0.4) among those exposed to STS compared to those who were unexposed. STS exposure is associated with an increase in circulating PRL but not TSH levels. Future studies are needed to confirm our results, identify biological mechanisms involved, and better understand the potential clinical and public health implications.

Neonatal thyroid-stimulating hormone concentrations in Belgium: a useful indicator for detecting mild iodine deficiency?

It has been proposed that neonatal thyroid-stimulating hormone (TSH) concentrations are a good indicator of iodine deficiency in the population. A frequency of neonatal TSH concentrations above 5 mU/L below 3% has been proposed as the threshold indicating iodine sufficiency. The objective of the present study was to evaluate feasibility and usefulness of nation-wide neonatal TSH concentration screening results to assess iodine status in Belgium. All newborns born in Belgium during the period 2009–2011 (n = 377713) were included in the study, except those suffering from congenital hypothyroidism and premature neonates. The frequency of neonatal TSH concentrations above 5 mU/L from 2009 to 2011 in Belgium fluctuated between 2.6 and 3.3% in the centres using the same TSH assay. There was a significant inverse association between neonatal TSH level and birth weight. The longer the duration between birth and screening, the lower the TSH level. Neonatal TSH levels were significantly lower in winter than in spring or autumn and significantly lower in spring and summer than in autumn while significantly higher in spring compared to summer. In conclusion, despite that pregnant women in Belgium are mildly iodine deficient, the frequency of neonatal TSH concentrations above 5 mU/L was very low, suggesting that the neonatal TSH threshold proposed for detecting iodine deficiency needs to be re-evaluated. Although neonatal TSH is useful to detect severe iodine deficiency, it should not be recommended presently for the evaluation of iodine status in mildly iodine deficient regions.

Smoking and early pregnancy thyroid hormone and anti-thyroid antibody levels in euthyroid mothers of the Northern Finland Birth Cohort 1986

BACKGROUND

Smokers in the general population have lower thyrotropin (TSH) and higher free triiodothyronine (fT3) and free thyroxine (fT4) concentrations, but the results in pregnant population vary from no effect to a decrease in TSH and fT4 concentrations and an increase in fT3 levels. Our objective was to further evaluate the question of whether there is an association between smoking, before and during pregnancy, with maternal thyroid function during pregnancy and with the risk for subsequent hypothyroidism.

METHODS

Our study population was a prospective population-based cohort (N=9362), the Northern Finland Birth Cohort 1986, with extensive data throughout gestation. The mothers underwent serum sampling in early pregnancy. The samples were assayed for TSH, fT3, fT4, thyroid-peroxidase antibodies (TPO-Ab), and thyroglobulin antibodies (TG-Abs) (n=5805). Mothers with thyroid dysfunction diagnosed before or during pregnancy were excluded, leaving 4837 euthyroid mothers. The smoking status of mothers and fathers were requested by questionnaires during pregnancy. Subsequent maternal morbidity relating to hypothyroidism 20 years after the index pregnancy was evaluated using national registers.

RESULTS

Euthyroid mothers who smoked before, or continued smoking during first trimester of pregnancy, had higher serum fT3 (p<0.001) and lower fT4 (p=0.023) concentrations than nonsmokers. Smoking in the second trimester was associated with higher fT3 (p<0.001) concentrations, but no difference in fT4 concentrations compared with nonsmokers. TG-Abs were less common among smoking than nonsmoking mothers (2.5% vs. 4.7%, p<0.001), but the prevalence of TPO-Ab was similar. Paternal smoking had no independent effect on maternal early pregnancy thyroid hormone or antibody concentrations. The risk of subsequent maternal hypothyroidism after follow-up of 20 years was similar among prepregnancy smokers and nonsmokers.

CONCLUSIONS

In euthyroid women, smoking during pregnancy was associated with higher fT3 levels and lower fT4 levels; possibly reflecting smoking-induced changes in peripheral metabolism of thyroid hormones. No differences were found in TSH concentrations between smokers and nonsmokers. Our results differ from those of the general population, which usually have shown smoking-induced thyroidal stimulation. This is possibly due to pregnancy-induced changes in thyroid function. Decreases in fT4 levels among smokers might predispose to hypothyroidism or hypothyroxinemia during pregnancy. Despite these changes in thyroid function, smoking did not increase the woman's risk of subsequent hypothyroidism.

Thyroid disorders during pregnancy

Thyroid disorders are common in women during pregnancy. If left untreated, both hypothyroidism and hyperthyroidism are associated with adverse effects on pregnancy and fetal outcomes. It is important to correctly identify these disorders and treat them appropriately to prevent pregnancy-related complications. Levothyroxine is the indicated treatment for hypothyroidism, and thionamides are the treatment of choice for hyperthyroidism; thyroidectomy may be indicated in select cases. When thyroid cancer is diagnosed during pregnancy, a decision must be made regarding performing thyroidectomy during the pregnancy or postponing surgical resection until the postpartum period. Radioactive iodine is absolutely contraindicated during pregnancy and lactation.

Maternal thyroid autoimmunity during pregnancy and the risk of attention deficit/hyperactivity problems in children: the Generation R Study

BACKGROUND

Maternal thyroid status and autoimmunity during pregnancy have been associated with impaired development of the offspring in animal and human studies. Our objective was to examine whether elevated titers of maternal thyroid peroxidase antibodies (TPOAbs) in early pregnancy increased the risk of cognitive impairment and problem behavior in preschool children. Second, we aimed at exploring to what extent any effect on child behavior was mediated by maternal thyroid parameters during pregnancy.

METHODS

In the Generation R Study, a population-based cohort of 3139 children and their mothers, we measured maternal thyroid parameters (thyrotropin [TSH], free Thyroxine, and TPOAbs) at 13.5±1.8 weeks of gestation. Children's verbal and nonverbal cognitive functioning was measured at 2.5 years using the Language Development Survey and the Parent Report of Children Abilities. At 3 years, children's behavior was assessed using the Child Behavior Checklist.

RESULTS

Elevated titers of TPOAbs during pregnancy did not predict the verbal and nonverbal cognitive functioning of the children. However, elevated titers of TPOAbs in mothers were associated with externalizing problems in children (odds ratio [OR]=1.64, 95% confidence interval [CI]: 1.17-2.29, p=0.004). In particular, children of TPOAb-positive mothers were at a higher risk of attention deficit/hyperactivity problems (OR=1.77, 95% CI: 1.15-2.72, p=0.01). To explore whether the effect of maternal TPOAbs on child problem behavior was mediated by maternal thyroid parameters, we added maternal TSH to the model. After correcting for TSH, the effect of TPOAbs on externalizing problems was attenuated slightly but remained significant (OR=1.56, 95% CI: 1.14, 2.14, p=0.005).

CONCLUSIONS

Our findings imply that the elevated titers of TPOAbs during pregnancy impact children's risk of problem behavior, in particular, attention deficit/hyperactivity. The observed effect is only partially explained by maternal TSH levels. These findings may point to a specific mechanism of Attention Deficit/Hyperactivity Disorder in children. Nevertheless, we can only speculate about public health implication of the study, as there is no specific treatment for TPOAb-positive pregnant women with normal thyroid function. Further investigation is needed to explore whether TPOAb-positive pregnant women and their children can benefit from close monitoring and early detection of developmental delay in populations at risk.

The influence of active and passive smoking during pregnancy on umbilical cord blood levels of vitamins A and E and neonatal anthropometric indices

Smoking during pregnancy has been shown to be detrimental for the developing fetus. The effects of active and passive maternal smoking on umbilical cord serum levels of vitamin A and vitamin E were examined. Secondary measures included anthropometric parameters in the newborn. Maternal and umbilical cord serum levels of vitamins A and E were measured at delivery. The mothers were assigned to three groups: non-smoking (n 12); passive smoking (n 13); active smoking (n 18). Based on multivariate linear regressions, active smoking during pregnancy was associated with increased umbilical cord serum levels of vitamin A and vitamin E. While enhanced circulating levels of vitamin A in cord blood were also found in non-smoking mothers exposed to tobacco smoke during pregnancy, those of vitamin E were not influenced. Further, an inverse association between smoking behaviour during pregnancy and birth length was observed, with shortest length in active smokers followed by passive smoking mothers. Active and passive maternal smoking behaviour during pregnancy increases the fetal demand for antioxidant compounds in order to counteract the oxidative burden by cigarette smoke. Against this background, the observed increase in umbilical cord serum levels of vitamins A and E may subserve antioxidative processes in response to tobacco smoke-induced oxidative stress. This would reduce the availability of vitamins A and E for fetal maturation, which is critical inasmuch as both compounds are indispensable for the developing fetus. However, due to the cross-sectional nature of our observation, this line of reasoning definitely requires validation in cause-effect experiments in the future.

Hypothyroidism among former workers of a nuclear weapons facility

BACKGROUND

Ionizing radiation alters thyroid function, and workers at a nuclear weapons facility may be exposed to above environmental levels of radiation.

METHODS

Hypothyroid status was determined for 622 former workers of a nuclear weapons facility located in Texas, using a combination of measured thyroid stimulating hormone (TSH) levels and thyroid medication history, as part of an on-going health surveillance program. We classified 916 unique job titles into 35 job categories.

RESULTS

According to the most stringent TSH definition used in this study (0.3-3.0 IU/ml), 174 (28.0%) former workers were considered to be hypothyroid; of these 66 (41.8%) were females and 108 (23.3%) were males. In logistic regression analysis adjusted for age, gender, and smoking status, only having worked as a material handler (n = 18) exhibited an elevated risk of developing hypothyroidism compared to other jobs (OR 3.88, 95% CI 1.43-11.07). This is one of the jobs with suspected exposure to radiation. No excess risk of hypothyroidism was observed for any of the other job categories.

CONCLUSIONS

There is suggestive evidence that only material handlers at this nuclear weapons facility may have elevated risk of hypothyroidism; further evaluation of thyroid health in this population is warranted.

Lower free thyroxin associates with a less favorable metabolic phenotype in healthy pregnant women

CONTEXT

A lower free T(4) (fT4), within the euthyroid range, has been shown in adults to associate with an adverse metabolic phenotype. Thyroid physiology changes significantly during gestation and affects maternal and fetal well-being.

OBJECTIVE

The aim of the study was to test the hypothesis that a lower serum fT4 in healthy euthyroid pregnant women is related to a less favorable metabolic phenotype and to fetal or placental weight. DESIGN, SETTING, PATIENTS, AND OUTCOME MEASURES: We examined associations of thyroid function tests (TSH and fT4) and the free T(3) (fT3)-to-fT4 ratio (as a proxy of deiodinase activity) with a metabolic profile [preload and postload glucose, glycosylated hemoglobin (HbA1c), high molecular-weight (HMW)-adiponectin, homeostasis model of assessment for insulin resistance (HOMA-IR), and serum lipids] in 321 healthy pregnant women. All women were euthyroid and had negative anti-thyroid peroxidase antibodies. None received thyroid hormone replacement. Blood tests were performed in women between 24 and 28 wk gestation. Placentas and newborns were weighed at birth.

RESULTS

Circulating TSH did not relate to metabolic parameters, but decreasing fT4 and increasing fT3-to-fT4 ratio associated with a less favorable metabolic phenotype, as judged by higher postload glucose, HbA1c, fasting insulin, HOMA-IR, and triglycerides, and by a lower HMW-adiponectinemia (all P ≤ 0.005). In multiple regression analyses, fT4 was independently associated with HbA1c (β = -0.135; P = 0.038), HMW-adiponectin (β = 0.218; P < 0.001), and placental weight (β = -0.185; P < 0.005), whereas the fT3-to-fT4 ratio was independently associated with maternal body mass index (β = 0.265; P < 0.001), HMW-adiponectinemia (β = -0.237; P < 0.002), HOMA-IR (β = 0.194; P = 0.014), and placental weight (β = 0.174; P = 0.020).

CONCLUSION

In pregnant women without a history of thyroid dysfunction, lower concentrations of fT4 and a higher conversion of fT4 to fT3, as inferred by changes in the fT3-to-fT4 ratio, were found to be associated with a less favorable metabolic phenotype and with more placental growth.

Cord blood thyroid tests in boys born with and without cryptorchidism: correlations with birth parameters and in utero xenobiotics exposure

BACKGROUND

In utero exposure to environmental chemicals can result in reproductive toxicity via endocrine disruption mechanisms. Whether some of those contaminants also have an impact on fetal thyroid function or pathways, and, thus, potentially on neuropsychological development, is still debated.

METHODS

We used samples from a cord blood (CB) and milk bank, established for a research on cryptorchidism and xenobiotic exposure to compounds known for their anti-androgenic and/or estrogenic activity, to study CB thyroid tests and their correlation with CB and milk xenobiotics concentrations in boys born in Nice area.

RESULTS

No difference was found in thyroid tests between 60 cryptorchid boys and 76 matched controls (median thyroid stimulating hormone 5.97 vs. 6.55 mUI/L, free thyroxine [fT4] 13.1 vs. 12.9 pmol/L, free triiodothyronine [fT3] 1.9 vs. 2.1 pmol/L), with no influence of season of birth, gestational age, maternal smoking, or mode of delivery (except for higher fT4 in control boys born vaginally). FT4 was correlated with fetal growth only in cryptorchid boys. Since we had previously shown differences between cryptorchid and controls exposure, we studied correlations of thyroid tests with xenobiotics in control boys only. All tested CB or maternal milk was contaminated by one or more selected xenobiotics, mainly polychlorinated biphenyls (PCBs), dichloro diphenyl dichloroethylène (DDE), dibutylphthalate, hexachlorobenzene, and bisphenol A. We found a significant negative correlation between fT4 and concentrations of PCB118, PC180, and DDE in milk (respectively r = -0.342, p < 0.03, r = -0.296, p = 0.031, r = -0.315, p = 0.016), persisting after adjustment for mode of delivery. There was a significant positive correlation of fT3 with milk concentrations of PCB138, PCB153, ΣPCB, and dibutylphthalate (respectively r = 0.31, p = 0.016, r = 0.28, p = 0.029; r = 0.34, p = 0.0079 and r = 0.272, p = 0.0295), with a trend for PCB180 (r = 0.259, p = 0.061). There was no correlation of thyroid stimulating hormone with any of the measured xenobiotics, except for a weak negative trend with CB bisphenol A (r = -0.25, p = 0.077).

CONCLUSIONS

CB thyroid tests are within normal range in cryptorchid boys, similar to controls. Our data in controls suggest a possible weak correlation between in utero exposure to some xenobiotics (PCBs, DDE) and fT3 and fT4 CB concentrations, with usually negative correlations with fT4 and positive with fT3 concentrations, which we speculate could suggest an impact on deiodinases.

Nutritional status of iodine in pregnant women in Catalonia (Spain): study on hygiene-dietetic habits and iodine in urine

Background

It is a priority to achieve an adequate nutritional status of iodine during pregnancy since iodine deficiency in this population may have repercussions on the mother during both gestation and post partum as well as on the foetus, the neonate and the child at different ages. According to the WHO, iodine deficiency is the most frequent cause of mental retardation and irrreversible cerebral lesions around the world. However, few studies have been published on the nutritional status of iodine in the pregnant population within the Primary Care setting, a health care level which plays an essential role in the education and control of pregnant women. Therefore, the aim of the present study is: 1.- To know the hygiene-dietetic habits related to the intake of foods rich in iodine and smoking during pregnancy. 2.- To determine the prevalence of iodine deficiency and the factors associated with its appearance during pregnancy.

Methods/design

We will perform a cluster randomised, controlled, multicentre trial. Randomisation unit: Primary Care Team. Study population: 898 pregnant women over the age of 17 years attending consultation to a midwife during the first trimester of pregnancy in the participating primary care centres. Outcome measures: consumption of iodine-rich foods and iodine deficiency. Points of assessment: each trimester of the gestation. Intervention: group education during the first trimester of gestation on healthy hygiene-dietetic habits and the importance of an adequate iodine nutritional status. Statistical analysis: descriptive analysis of all variables will be performed as well as multilevel logistic regression. All analyses will be done carried out on an intention to treat basis and will be fitted for potential confounding factors and variables of clinical importance.

Discussion

Evidence of generalised iodine deficiency during pregnancy could lead to the promotion of interventions of prevention such as how to improve and intensify health care educational programmes for pregnant women.

Trial Registration

ClinicalTrials.gov: NCT01301768