Validation of Billewicz Scoring System for Detection of Overt Hypothyroidism During Pregnancy

AUTHORS

Sima Nazarpour 1 , 2 , Fahimeh Ramezani Tehrani 2 , * , Maryam Rahmati 2 , 3 , Sonia Minooee 2 , Masoumeh Simbar 4 , Mahsa Noroozzadeh 2 , Fereidoun Azizi 5

1 Department of Midwifery, Varamin-Pishva Branch, Islamic Azad University, Tehran, IR Iran

2 Reproductive Endocrinology Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran

3 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, IR Iran

4 Midwifery and Reproductive Health Research Center, Department of Midwifery and Reproductive Health, School of Nursing and Midwifery, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran

5 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran

How to Cite: Nazarpour S, Ramezani Tehrani F, Rahmati M, Minooee S, Simbar M, et al. Validation of Billewicz Scoring System for Detection of Overt Hypothyroidism During Pregnancy, Int J Endocrinol Metab. 2018 ; 16(3):e64249. doi: 10.5812/ijem.64249.

ARTICLE INFORMATION

International Journal of Endocrinology and Metabolism: 16 (3); e64249
Published Online: July 7, 2018
Article Type: Research Article
Received: November 20, 2017
Revised: June 12, 2018
Accepted: June 23, 2018
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Abstract

Background: Currently, various clinical and laboratory diagnostic methods are used to detect overt hypothyroidism during pregnancy. The Billewicz scoring index, as a clinical scale for detection of hypothyroidism, has been applied in general populations; however, its application during pregnancy remains a controversial subject of ongoing research.

Objectives: The purpose of this study was to evaluate the diagnostic value of Billewicz scoring index for overt hypothyroidism in a general population of Iranian pregnant women.

Methods: This study was conducted on 1843 pregnant women. A comprehensive questionnaire, including Billewicz scoring items, was completed, and relevant clinical examinations were performed. The participants underwent serum measurements of thyroxine (T4), thyroid hormone uptake, thyroid-stimulating hormone (TSH), and thyroid peroxidase antibody (TPOAb). Using the receiver operating characteristic (ROC) curve analysis, the optimal sensitivity and specificity were determined as values with maximum yields on the Youden and Rsquo’s Index (sensitivity + specificity-1).

Results: The prevalence of overt hypothyroidism and subclinical hypothyroidism was 3.3% and 28.6%, respectively. Overall, 3.6%, 18.9%, and 50% of euthyroid, subclinical hypothyroid, and overt hypothyroid women were TPOAb-positive, respectively. The mean Billewicz scores of euthyroid, overt hypothyroid, and subclinical hypothyroid women were -41.16 (11.16), -17.11 (13.63), and -40.1 (11.2), respectively. Based on the Billewicz scale, at least one sign of hypothyroidism was reported in 38.84% (n, 491) of euthyroid women. Scores ≤ -26.5 (sensitivity, 100%; specificity, 90.82%) were considered as the optimal scores for predicting overt hypothyroidism (Ldquo, Norisk, and Rsquo).

Conclusions: The Billewicz clinical scoring system, as a reliable and inexpensive clinical tool, used along with laboratory measurements, can help screen overt hypothyroidism during pregnancy, primarily in low-resource settings.

Keywords

Hypothyroidism Signs and Symptoms Pregnancy

Copyright © 2018, International Journal of Endocrinology and Metabolism. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited

1. Background

Thyroid disorders are the second most frequent endocrine disorder in women of childbearing age (1). Hypothyroidism, with a prevalence of 2% - 5%, is the most common gestational thyroid dysfunction (2, 3). According to previous reports, the prevalence of hypothyroidism (both overt and subclinical) is estimated at 4.7% in Iranian pregnant women (4). Numerous studies have addressed the adverse effects of overt hypothyroidism (OH) on pregnancy outcomes (5-7), despite controversies about the adverse fetal-maternal effects of subclinical hypothyroidism (SCH) (8). Proper screening can lead to early diagnosis of these disorders in pregnancy. However, universal screening for diagnosis of thyroid dysfunction in pregnancy is a controversial topic (9, 10).

Evidence shows that the selective high-risk case-finding approach may overlook a considerable number of gravid women with overt thyroid dysfunction (11, 12). As a result, having access to a convenient tool with an acceptable diagnostic value in detecting thyroid disorders during pregnancy has its merits. Apart from the universally advocated laboratory assessment of thyroid function, several questionnaires have been designed for diagnosis of thyroid dysfunctions (13). These clinical tools are definitely not intended to replace blood measurements, but are reliable tools in low-income settings with limited access to costly tests; they can be also useful in posttreatment follow-ups.

Although validity of these clinical tools has been confirmed in general populations, no published study is available about their validation for pregnant women. Among various available tools, the Billewicz scoring index, as a cost-effective clinical index, was validated against thyroid iodine uptake and plasma protein-bound iodine in 1969 and against thyroid-stimulating hormone (TSH), triiodothyronine (T3), and free thyroxine (FT4) in 1997 (14, 15). Despite the convenience and accuracy of this tool in diagnosis of hypothyroidism in general populations, no information exists regarding Billewicz scale verification during pregnancy; therefore, the optimal pregnancy-related cut-off value has not been established yet.

In the present study, we aimed to assess the validity of Billewicz scale in a pregnant population, selected from Tehran thyroid and pregnancy study (TTAPS) to determine the optimal cut-off point of the Billewicz index with the highest sensitivity and specificity for predicting OH.

2. Methods

Data were collected from the first phase of TTAPS, which was carried out on pregnant women, attending the prenatal clinics of Shahid Beheshti Medical University. The details of TTAPS are published in the literature (16). All women were screened for thyroid dysfunction by collecting information from their medical history, clinical examinations, and serum thyroid peroxidase antibody (TPOAb), TSH, T4, and T-uptake measurements. They were then classified as follows: normal thyroid, OH, overt hyperthyroidism, TPOAb-positive euthyroidism, SCH, and subclinical hyperthyroidism. Subjects with twin pregnancies (n, 27) or history of chronic disorders were excluded from the study. Of a total of 1,843 pregnant women, 1,264, 38, and 541 cases exhibited euthyroidism, OH, and SCH, respectively.

In this study, the Billewicz scale was applied. This scale was developed based on seven symptoms and six signs, which were typically associated with hypothyroidism. According to this scale, higher positive scores indicate a higher level of clinical hypothyroidism. Items are weighed differently, based on their frequency of occurrence (see supplementary file, appendix 1) (13). A questionnaire related to the symptoms described in the Billewicz scale was completed, and a thorough physical examination of Billewicz signs (i.e., slow movement, coarse skin, cold skin, periorbital puffiness, bradycardia, and delayed ankle reflex) was performed. After collection and centrifugation of fasting blood samples, the sera were sent to the Research institute of endocrine sciences of Shahid Beheshti University of Medical Sciences for laboratory assessments.

Using radioimmunoassay and immunoradiometric assay, T4 and TSH levels were measured, respectively by commercial kits (Izotop Kit, Budapest Co., Hungary) and a gamma counter (Dream Gamma-10, Goyang-si, Gyeonggi-do, South Korea). T-uptake and TPOAb were also determined by the enzyme immunoassay (Diaplus Kit, San Francisco, CA, USA) and immunoenzymometric assay (Monobind Kit, Costa Mesa, CA, USA), respectively, using a calibrated ELISA reader (Sunrise, Tecan Co., Salzburg, Austria). The inter- and intraassay coefficients of variation for T4, T-uptake, TSH, and TPOAb were 1.1%, 3.9%, 2.2%, and 4.3% and 1.9%, 4.7%, 1.0%, and 1.6%, respectively.

2.1. Definitions

Overt hyperthyroidism was defined as TSH level < 0.1 μIU/mL and FT4I > 4.5. OH was defined as TSH > 10 μIU/mL or TSH > 2.5 μIU/mL and FT4I < 1. SCH was defined as normal FT4I (1-4.5), despite elevated TSH (2.5-10 μIU/mL). Finally, subjects with TPOAb > 50 IU/mL were considered TPOAb-positive. It should be noted that when we first designed TTAPS and initiated data acquisition (from September 2013 to February 2016), the available guideline was the previous American thyroid association guideline (10). Accordingly, SCH was defined based on the common TSH cut-point of 2.5 μIU/mL instead of the recently recommended cut-point of 4.0 μIU/mL (17). In the Billewicz questionnaire, more than a 1.5-fold increase in weight (e.g., more than 8 kg in the second trimester for those with a normal prepregnancy BMI) was considered as abnormal weight gain. Also, bradycardia was defined as pulse rate < 75 bpm.

2.2. Ethics Approval

Written informed consents were obtained from all the participants, and the study was approved by the ethics committee of research institute of endocrine sciences (code, IR.SBMU.ENDOCRINE.REC.1396.383).

2.3. Statistical Analysis

Continuous variables were assessed for normality using one-sample Kolmogorov-Smirnov test. Categorical variables, expressed as percentages, were compared using Pearson’s Chi square test. Normal continuous variables were compared between the three groups, using one-way ANOVA test and expressed as mean (standard deviation). Variables without a normal distribution were expressed as median (interquartile) and compared using Kruskal-Wallis test.

First, we classified our participants into three groups, using the cut-off values reported by Billewicz and colleagues: score ≥ +25 for OH; score of -30 to +25 (above -30 and below +25) for SCH; and score ≤ –30 for excluding hypothyroidism. A receiver operating characteristics (ROC) curve analysis was performed, and the optimal cut-off value was identified, using the Youden index for differentiating OH from euthyroidism. In fact, the Youden index maximizes the difference between sensitivity and 1-specificity (Youden index: sensitivity + specificity-1). Therefore, by excluding SCH patients and maximizing sensitivity + specificity-1 across various cut-off points for the Billewicz index, the optimal cut-off point was calculated to distinguish between healthy subjects and patients with OH (18). Data were analyzed using SPSS version 22, and level of significance was set at P < 0.05.

3. Results

The mean (SD) age, BMI, and gestational age of the participants were 26.6 (5.3) years, 25.1 (4.6) kg/m2, and 11.8 (4.1) weeks, respectively. Table 1 presents the characteristics of the study population according to their thyroid status. The median and interquartile range for TSH in euthyroid, OH, and SCH women were 1.46 (0.81 - 1.91), 7.92 (3.32 - 11.24), and 3.79 (3.06 - 4.96) μIU/mL, respectively. These values show that women with OH had significantly higher TSH levels, compared to the other two groups.

Table 1. Characteristics of the Study Population According to Their Thyroid Statusa
CharacteristicsEuthyroidism (n, 1264)Subclinical Hypothyroidism (n, 541)Overt Hypothyroidism (n, 38)P Value
Age, yb26.68 ± 5.3026.32 ± 5.1627.84 ± 5.010.140
Body mass index, kg/m2b24.85 ± 4.53c25.62 ± 4.75d27.47 ± 5.47< 0.001
Gestational age, wke11 (8 - 14)d12 (8 - 16)10 (7 - 14)< 0.001
Gestational age < 14 wkf880 (69.81)332 (61.5)d25 (65.8)0.003
Primigravidaf442 (35)213 (39.4)16 (42.1)0.156
TSHc1.46 (0.81 - 1.91)d3.79 (3.06 - 4.96)g7.92 (3.32 - 11.24)c< 0.001
T4e10.5 (8.8 - 12.5)10.3 (8.7 - 12.4)10.2 (8.4 - 13.02)0.320
FTIe2.9 (2.5 - 3.4)2.8 (2.3 - 3.2)d2.8 (2.3 - 3.22)0.420
TPOAbe4 (2 - 8)d7 (3 - 28)g46 (5.5 - 445)c< 0.001
T3 uptakee28 (25 - 30)c27 (24 - 29)d26.5 (23 - 29)< 0.001

Abbreviations: FTI, free thyroxine index; TPOAb, thyroid peroxidase antibody; TSH, thyroid stimulating hormone.

aValues are expressed as mean ± SD, Median (IQR), or No. (%).

bANOVA.

cSignificant difference between overt hypothyroidism and euthyroidism.

dSignificant difference between subclinical hypothyroidism and euthyroidism.

eKruskal-Wallis test was used to compare the groups whenever needed.

fChi square.

gSignificant difference between subclinical hypothyroidism and overt hypothyroidism.

The mean±SD age of OH, euthyroid, and SCH women was 27.84 ± 5.01, 26.68 ± 5.30, and 26.32 ± 5.16 years, respectively. Euthyroid women had a significantly lower BMI, compared to OH and SCH groups (24.85 ± 4.53 versus 27.47 ± 5.47 and 25.62 ± 4.75). The prevalence of TPOAb positivity was 3.6%, 18.9%, and 50% in euthyroid, SCH, and OH groups, respectively. In addition, the median and interquartile range of TPOAb in euthyroid, OH, and SCH groups were 4 (2 - 8), 46 (5.5 - 445), and 7 (3 - 28) μIU/mL, respectively (Table 1).

Distribution of various risk factors for thyroid disorders showed that history of levothyroxine treatment and history of thyroid dysfunction were the two most common risk factors for OH in women. Also, age ≥ 30 years and thyroid antibodies, primarily TPOAb, were the most common risk factors for SCH (Table 2). Among euthyroid pregnant women, 491 (38.5%) exhibited at least one sign or symptom of the Billewicz index. Based on the findings, 257 (47.5%) and 34 (89.5%) SCH and OH women had more than (or equal to) one Billewicz sign or symptom, respectively. The mean ± SD Billewicz score was -17.11 ± 13.63 in the OH group, which is significantly different from that of euthyroid (-41.16 ± 11.16; P < 0.001) and SCH (-40.1 ± 11.2; P < 0.001) women.

Table 2. Risk Factors for Thyroid Disorders in the Participants According to Their Thyroid Statusa
Risk FactorsEuthyroidism (n, 1264)Subclinical Hypothyroidism (n, 541)Overt Hypothyroidism (n, 38)P Value
History of thyroid dysfunction26 (2.1)b35 (6.5)c22 (57.9)d< 0.001
History of levothyroxine treatment7 (0.6)b1 (0.2)c23 (60.5)d< 0.001
History of treatment with radioactive iodine2 (0.2)0 (0.0)0 (0.0)-
History of therapeutic head or neck irradiation or thyroid surgery0 (0.0)b2 (0.4)1 (2.6)d-
Family history of autoimmune thyroid disease or thyroid127 (10.1)b76 (14)c11 (28.9)d< 0.001
Goiter25 (2)b6 (1.1)c4 (10.5)< 0.001
TPOAb45 (3.6)b102 (18.9)c19 (50)d< 0.001
Type I diabetes mellitus or other autoimmune disorders13 (1)b0 (0.0)0 (0.0)-
History of miscarriage200 (15.9)89 (16.5)6 (15.8)0.951
History of preterm delivery21 (3.0)8 (3.0)0 (0.0)0.758
Infertility62 (4.9)23 (4.3)c8 (21.1)d< 0.001
Morbid obesity (BMI ≥ 40)7 (0.6)1 (0.2)c2 (6.1)d-
Age ≥ 30 y387 (30.7)144 (26.6)16 (42.1)0.054

Abbreviation: TPOAb, thyroid peroxidase antibody.

aValues are expressed as No. (%). Chi square test was used to compare the groups. Significance level was set at P < 0.05.

bSignificant difference between subclinical hypothyroidism and euthyroidism.

cSignificant difference between subclinical hypothyroidism and overt hypothyroidism.

dSignificant difference between overt hypothyroidism and euthyroidism.

Weakness/fatigue and laziness/sleepiness were the two most common symptoms in all the groups (Table 3). In total, 34 out of 38 women with OH showed delayed ankle reflexes; this sign was observed in six out of 541 women with SCH and 10 out of 1,264 euthyroid pregnant women. In addition, pulse rate < 75/minute was observed in 23.7%, 21.8%, and 15.4% of women with OH, SCH, and euthyroidism, respectively (Table 3).

Table 3. Signs and Symptoms of the Patients According to the Billewicz Index Based on Their Thyroid Statusa
Symptoms and SignsEuthyroidism (n, 1264)Subclinical Hypothyroidism (n, 541)Overt Hypothyroidism (n, 38)P Value
Symptoms
Diminished sweating22 (1.7)4 (0.7)-0.193
Dry skin85 (6.7)48 (8.9)3 (7.9)0.276
Cold intolerance130 (10.3)62 (11.5)8 (21.1)0.095
Weight gain34 (2.7)23 (4.3)2 (5.3)0.173
Constipation159 (12.6)91 (16.80)b8 (21.1)c0.026
Hoarseness12 (3)4 (2.7)-0.849
Hearing impairment8 (2)10 (6.8)b-0.015
Weakness/fatigue407 (32.2)161 (29.8)14 (36.8)0.463
Laziness/sleepiness264 (20.9)156 (28.8)b14 (36.8)c< 0.001
Signs
Slow movement36 (9.0)13 (8.9)3 (30)0.077
Coarse skin85 (6.7)48 (8.9)3 (7.9)0.276
Periorbital puffiness53 (12.7)26 (16.3)4 (30.8)0.121
Cold skin85 (6.7)48 (8.9)3 (7.9)0.276
Pulse rate (< 75/min)195 (15.4)118 (21.8)b9 (23.7)c0.003
Delayed ankle reflex10 (0.8)6 (1.1)34 (89.5)c< 0.001

aValues are expressed as No. (%).Chi square test was used to compare the groups. The significance level was set at P < 0.05.

bSignificant difference between subclinical hypothyroidism and euthyroidism.

cSignificant difference between overt hypothyroidism and euthyroidism.

Using the cut-off point suggested by Billewicz et al. (score ≥ +25 for OH; -30 to +25 [> -30 and < +25] for SCH; and ≤ -30 for excluding hypothyroidism), we observed a significant difference in the TSH level of OH patients and those with SCH and euthyroidism. Based on these cut-off values, 474 (29.4%) out of 1613 participants were categorized as the normal group, while based on the TSH levels, they were categorized as SCH. Also, 125 (54.3%) and 38 (16.5%) out of 230 women, who were categorized as euthyroid and OH based on the TSH values, respectively, were diagnosed with SCH. On the other hand, no subject was diagnosed with OH based on the Billewicz score, as the maximum score of Billewicz index is +24.

The mentioned values corresponded to sensitivities of 12.38%, 100%, and 100% and specificities of 90.11%, 90.11%, and 87.61% for distinguishing euthyroidism from SCH, euthyroidism from OH, and SCH from OH, respectively. These values yielded positive predictive values of 34.89%, 23.31%, and 36.19% and negative predictive values of 70.61%, 100%, and 100%, respectively in discrimination between euthyroidism and SCH, euthyroidism and OH, and lastly SCH and OH.

By excluding the data of SCH patients and maximizing sensitivity + specificity-1 across various cut-off points of the Billewicz index, an optimal cut-off point of -26.5 was obtained for distinguishing between normal individuals and patients with OH. The AUC of the Billewicz index for predicting the absence of risk for OH was approximately 0.93 (95% CI, 0.92 - 0.95; P < 0.001). The Billewicz score ≤ -26.5 corresponded to a sensitivity of 100% and specificity of 90.82% and yielded a positive predictive value of 24.67% for distinguishing euthyroidism from OH (this cut-off point corresponded to a positive likelihood ratio of 10.89 and a negative likelihood ratio of 0) (Figure 1).

The ROC curve analysis for diagnosis of overt hypothyroidism (OH)
Figure 1. The ROC curve analysis for diagnosis of overt hypothyroidism (OH)

4. Discussion

The results of this study suggest that despite confusions in identifying thyroid disorders during pregnancy due to physiological changes, the Billewicz scoring index is a valid scale for diagnosis of gravid women with OH. The optimal cut-off point was -26.5, with sensitivity of 100%, specificity of 90.82%, and positive predictive value of 24.67%. Our findings, validating the accuracy of Billewicz index during pregnancy, are novel, and to the best of our knowledge, no study has been published in this field so far.

We noted that delayed ankle reflex, fatigue, weakness, sleepiness, laziness, pulse rate < 75/min, constipation, and cold intolerance were the most common signs and symptoms of OH. In accordance with our findings, in a study by Galia et al. the most frequent symptoms in hypothyroid non-pregnant patients were easy fatigue (64%), dyspnea on effort (52%), weight gain (44%), and constipation (44%), while the most common signs were rough and dry skin (36%), thyroid enlargement (32%), and sluggish movement (32%) (19). Almost similarly, Zulewski et al. reported weight gain (54%), constipation (48%), dry skin (76%), and bradycardia (58%) as the most common manifestations of hypothyroidism, which are comparable to the current study (15).

We also noticed that all signs and symptoms, except for three (diminished sweating, hoarseness, and hearing impairment), were present in both euthyroid and hypothyroid women. However, only four items, including laziness/sleepiness, constipation, ankle jerk reflex, and pulse rate < 75/m, were significantly higher in hypothyroid women, compared to their euthyroid counterparts; therefore, there is a lower risk of overlap with pregnancy-related physiological changes. Since physiological changes of pregnancy may mimic thyroid dysfunction signs, accurate diagnosis of hypothyroidism, based on the common signs and symptoms used in non-pregnant populations, is problematic (20). Meanwhile, laboratory measurements of thyroid function need to be interpreted cautiously during pregnancy, compared to non-pregnant women (17).

Screening of thyroid disorders during pregnancy has been a long-disputed issue. Universal screening and targeted high-risk case-finding have their own advantages and disadvantages (17). Overall, universal thyroid screening is a common and cost-effective approach; however, there are still controversies about its application, since the prevalence of thyroid dysfunctions varies in different racial and ethnic populations (21); therefore, the significance of universal screening may be diminished among low-risk groups. In addition, there are still areas of uncertainty and disagreement among experts about the beneficial impact of maternal SCH diagnosis and management of poor pregnancy outcomes (22, 23).

A recent guideline of the American thyroid association declared that there is insufficient information to recommend or argue against universal screening during pregnancy, and TSH tests are recommended for women with the risk factors (17). On the other hand, the selective case-finding approach fails to identify about one-third of women with OH or SCH (24), which is considered a significant disadvantage for a screening test. Furthermore, challenging limitations, such as high cost of laboratory tests and endocrinologist visits, maternal anxiety, and absence of trimester-specific reference ranges, may necessitate validation of a preexisting reliable scale.

The Billewicz scale, appraised as one of the most cited thyroid scoring indices worldwide (25), has the potential to fill the mentioned gaps. This index serves as an inexpensive and accurate tool, basically for high-risk populations from low- and middle-income countries with limited access to costly laboratory tests. We agree that despite the strong association between clinical symptoms and abnormal TSH level (26), the accuracy of clinical diagnosis is limited, and laboratory diagnosis is also needed. Yet, we emphasize that the Billewicz index is not intended to replace sensitive biochemical measurements, but is a useful tool in detecting high-risk women prior to serum testing and can be applicable for measuring the patient’s response to medical treatment.

While the consequences of OH for pregnancy outcomes and neonatal/child development are well-established (5, 6), findings regarding the relationship between maternal SCH and adverse pregnancy outcomes in both mothers and neonates are contradictory. Current evidence does not support the lower level of intellectual development in children born to mothers with SCH (27), and data on the beneficial effects of thyroxine supplementation on SCH women are inconsistent (28). Therefore, identifying OH during pregnancy screening is a principal issue. Undoubtedly, undetected OH is associated with increased maternal and neonatal complications (5, 6, 29). However, even in the event of severe maternal hypothyroidism, neurocognitive deficiencies in the child may not occur once the condition is managed immediately in the first half of pregnancy; therefore, use of the Billewicz scale can decrease undiagnosed OH during pregnancy screening.

This study has one limitation. Instead of using the newly recommended limit of 4.0 μIU/mL, we defined SCH based on the TSH cut-off point of 2.5 μIU/mL according to the available guideline during study design and conception (September 2013 to February 2016). Considering the difference between the previous (12) and new (17) guidelines, a number of our euthyroid subjects might be classified as SCH patients. Euthyroid women had a significantly lower BMI, compared to the OH and SCH groups. However, this difference is not significant enough to influence the cut-off points; accordingly, there is no need to present age-BMI specific cut-off points.

4.1. Conclusions

In summary, this is a novel study, validating the Billewicz scale and identifying the cut-off points during pregnancy. We found that the Billewicz index could be simply used as an auxiliary diagnostic tool in resource-constrained settings. However, future studies should include pregnant women from different ethnic or geographic (in terms of iodine sufficiency) populations.

Acknowledgements

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