European Journal of Cardiovascular Medicine

The interplay between pregnancy and thyroid function is a complex, dynamic process with significant implications for maternal and fetal health. Thyroid disorders, encompassing both hypothyroidism and hyperthyroidism, represent some of the most prevalent endocrine conditions affecting pregnant women. These disorders can lead to adverse pregnancy outcomes, including preeclampsia, gestational hypertension, premature birth, low birth weight, and increased perinatal morbidity and mortality[1]. Therefore, understanding the prevalence and impact of thyroid disorders during pregnancy is crucial for optimizing antenatal care.

The prevalence of thyroid disorders in pregnancy varies globally, influenced by iodine intake, geographic region, and screening practices[2]. Hypothyroidism, characterized by insufficient thyroid hormone production, is the most common thyroid disorder in pregnancy. The condition can be subcategorized into clinical (overt) and subclinical hypothyroidism, with the latter being more prevalent. Studies indicate that the prevalence of hypothyroidism during pregnancy ranges from 2% to 3% for overt hypothyroidism and 2% to 15% for subclinical hypothyroidism, depending on the population studied and the diagnostic criteria used[3].

Hyperthyroidism, though less common than hypothyroidism, occurs in approximately 0.1% to 0.4% of all pregnancies[4]. The most frequent cause of hyperthyroidism during pregnancy is Graves' disease, which poses risks to both the mother and the fetus, including heart failure, preterm birth, and fetal growth restriction.

The management of thyroid disorders in pregnancy is further complicated by the physiological changes in thyroid function that occur during gestation. These changes can mask or simulate thyroid disease, making diagnosis and treatment challenging. The American Thyroid Association (ATA) and other expert bodies have issued guidelines for the screening and management of thyroid disorders in pregnancy, emphasizing the need for tailored therapeutic approaches based on individual risk factors and thyroid function tests[5].

Given the significant impact of thyroid disorders on pregnancy outcomes, recent research has focused on early detection and intervention. Universal screening for thyroid dysfunction in early pregnancy has been proposed as a strategy to reduce adverse outcomes, though its implementation remains controversial due to cost-effectiveness and the potential for overdiagnosis[6].

This article aims analyse the prevalence of thyroid disorders in pregnancy, exploring the epidemiological trends, diagnostic challenges, and clinical implications. By synthesizing recent data and guidelines, we seek to provide a comprehensive overview that informs clinical practice and guides future research in this vital area of maternal-fetal medicine.

Aims and Objectives

The primary aim of this prospective observational study was to estimate the prevalence of thyroid disorders among pregnant women over a duration of six months. Specifically, the study focused on identifying the incidence of hypothyroidism, hyperthyroidism, and subclinical thyroid disorders during various trimesters of pregnancy. The secondary objectives included assessing the impact of thyroid dysfunction on pregnancy outcomes, including gestational age at delivery, birth weight, and the rate of obstetric complications such as preeclampsia and gestational diabetes.

Study Design and Setting

The research was conducted as a prospective observational study at a tertiary care hospital's antenatal clinic over a period of six months. The study received approval from the Institutional Review Board, ensuring compliance with ethical standards and patient confidentiality.

Participants

The study enrolled a total of 500 pregnant women in their first trimester, identified through consecutive sampling. The inclusion criteria were: singleton pregnancy, age 18-45 years, and gestational age up to 13 weeks at the time of enrollment. Exclusion criteria included known pre-existing thyroid disorders, current use of thyroid medication, and history of thyroid surgery or radioactive iodine therapy.

Procedures

Following informed consent, participants underwent a comprehensive initial assessment that included a detailed medical history, physical examination, and baseline thyroid function tests (TFTs), including Thyroid Stimulating Hormone (TSH), Free Thyroxine (FT4), and Anti-Thyroid Peroxidase (Anti-TPO) antibodies. Follow-up TFTs were conducted in each trimester to monitor changes in thyroid function. Ultrasound examinations of the thyroid gland were performed at enrollment and at the end of the study to detect structural abnormalities.

Data Collection

Data were collected using a structured questionnaire and electronic medical records. The questionnaire covered demographic information, obstetric history, symptoms of thyroid dysfunction, and lifestyle factors such as dietary iodine intake. Clinical data included TFT results, ultrasound findings, pregnancy outcomes (e.g., gestational age at delivery, birth weight), and any obstetric complications.

Statistical Analysis

Descriptive statistics were used to summarize demographic and clinical characteristics of the study population. The prevalence of thyroid disorders was calculated as the proportion of participants diagnosed with hypothyroidism, hyperthyroidism, or subclinical thyroid dysfunction during the study period. Chi-square and Fisher's exact tests were employed to examine the association between thyroid disorders and obstetric outcomes. Logistic regression analysis was used to identify potential risk factors for thyroid dysfunction in pregnancy. All analyses were performed using SPSS version 25.0, with a p-value of less than 0.05 considered statistically significant.

Sample Size Determination

The sample size of 500 was calculated based on an expected prevalence rate of thyroid disorders in pregnancy of 10%, with a confidence level of 95% and a margin of error of 5%. This sample size was deemed sufficient to provide adequate power for the statistical analysis of the primary and secondary objectives.

The study sought to investigate the prevalence of thyroid dysfunction among pregnant women and its correlation with obstetric outcomes, risk factors, and treatment compliance. A total of 500 pregnant women participated in the study, with a mean age of 30 years (SD ± 5), a body mass index (BMI) of 25 kg/m² (SD ± 4), and were on average 10 weeks gestational age (SD ± 2) at the time of enrollment. The distribution of parity among participants was evenly spread with 200 (40%) nulliparous, 150 (30%) having one previous pregnancy, and 150 (30%) with two or more pregnancies. Only a small fraction, 50 (10%), reported smoking status as 'Yes'.

The overall prevalence of thyroid dysfunction identified in the cohort was 5.0%, with 25 cases detected. Specifically, hypothyroidism was observed in 10 participants (2.0%), hyperthyroidism in 5 (1.0%), subclinical hypothyroidism in 8 (1.6%), and subclinical hyperthyroidism in 2 (0.4%). The prevalence of thyroid dysfunction varied across the trimesters: in the first trimester, hypothyroidism, hyperthyroidism, subclinical hypothyroidism, and subclinical hyperthyroidism were found in 1.0%, 0.6%, 0.8%, and 0.2% of the participants, respectively. The second trimester showed a slight decrease in prevalence rates, and the third trimester demonstrated further reductions.

The association between thyroid dysfunction and obstetric outcomes revealed a higher incidence of preterm birth (20% vs. 9%, Odds Ratio [OR] 2.5, 95% CI 0.9-6.8, p=0.08) and low birth weight (16% vs. 8%, OR 2.1, 95% CI 0.7-6.1, p=0.18) in women with thyroid dysfunction, although these findings did not reach statistical significance. Preeclampsia was more common in women with thyroid dysfunction (12% vs. 4%, OR 3.2, 95% CI 0.9-11.2, p=0.07). No significant association was found between thyroid dysfunction and gestational diabetes (8% vs. 6%, OR 1.3, 95% CI 0.3-5.7, p=0.73).

Ultrasound findings in women with thyroid dysfunction showed that 16% had goiter, 12% had thyroid nodules, and 72% had a normal ultrasound. This indicates that a significant proportion of thyroid dysfunction cases might not be detectable through ultrasound alone.

Analysis of risk factors for thyroid dysfunction highlighted that being over 30 years of age significantly increased the risk (OR 2.0, 95% CI 1.1-3.6, p=0.02), as did having a family history of thyroid disease (OR 3.5, 95% CI 1.8-6.9, p=0.001). BMI ≥ 30 kg/m² showed a trend towards increased risk but was not statistically significant (OR 1.8, 95% CI 0.9-3.5, p=0.09). Smoking did not significantly affect the risk of developing thyroid dysfunction (OR 1.2, 95% CI 0.4-3.6, p=0.74).

The data reveal a profoundly significant correlation. The incidence of abortion was markedly higher in the group with thyroid dysfunction, at 24%, compared to just 3% in those without thyroid dysfunction. This yielded an odds ratio (OR) of 9.0, with a 95% confidence interval (CI) stretching from 3.5 to 23.2, and a highly significant p-value of <0.001.

Follow-up thyroid function test results showed an increase in TSH and a decrease in FT4 levels from the first to the third trimester, indicating a worsening of thyroid function over the course of the pregnancy. Specifically, there was an increase in TSH from an initial mean of 2.5 mIU/L (SD ± 1.2) to 2.9 mIU/L (SD ± 1.4), marking a 16% increase, and a decrease in FT4 from 1.2 ng/dL (SD ± 0.3) to 1.0 ng/dL (SD ± 0.2), reflecting a 16% decrease.

Regarding treatment compliance, among those prescribed levothyroxine, 20 participants were compliant while 5 were not, citing forgetfulness (n=3) and side effects (n=2) as reasons for non-compliance. All five participants prescribed antithyroid medication were compliant with their treatment regimen.

In summary, the study revealed a 5.0% prevalence of thyroid dysfunction among pregnant women, with a notable but not statistically significant association with adverse obstetric outcomes. Age over 30 years and a family history of thyroid disease were significant risk factors. The follow-up results indicated progressive thyroid function deterioration during pregnancy among affected women. Compliance with treatment was high, except in a small number of cases.

Table 1: Characteristics of the Study Population

Table 2: Prevalence of Thyroid Dysfunction

Table 3: Trimester-wise Prevalence of Thyroid Dysfunction

Table 4: Association between Thyroid Dysfunction and Obstetric Outcomes

Table 5: Ultrasound Findings in Women with Thyroid Dysfunction

Table 6: Risk Factors for Thyroid Dysfunction

Table 7: Follow-up Thyroid Function Test Results

Table 8: Compliance with Treatment and Follow-up

The prevalence of thyroid dysfunction among pregnant women in this study was found to be 5.0%, which is slightly higher than the anticipated global prevalence of approximately 3% based on prior research[7]. Our findings of hypothyroidism (2.0%) and hyperthyroidism (1.0%) prevalence are consistent with reported ranges in the literature, though at the lower end of the spectrum for hypothyroidism, which has been reported as high as 2-3% for overt hypothyroidism and 2-15% for subclinical hypothyroidism in different populations[8]. The variation in prevalence rates across studies can be attributed to differences in screening methodologies, diagnostic criteria, and population iodine status[9].

The lack of statistically significant association between thyroid dysfunction and adverse obstetric outcomes such as preterm birth and low birth weight in our study contrasts with previous research. For instance, Casey et al.[10] found a significant association between subclinical hypothyroidism and preterm birth (OR 1.7, 95% CI 1.1-2.6, p<0.05). The discrepancy may be due to our relatively small sample size for subgroups with thyroid dysfunction, limiting the statistical power to detect significant differences.

Our study identified age over 30 years and a family history of thyroid disease as significant risk factors for thyroid dysfunction during pregnancy, aligning with findings from Lazarus et al.[11], who also reported these factors as associated with increased risk. However, our study did not find a significant association between BMI and thyroid dysfunction, which contrasts with findings from a meta-analysis by Touliset al.[12], suggesting that higher BMI is a risk factor for hypothyroidism in the general population.

Follow-up results indicating a worsening of thyroid function (increase in TSH and decrease in FT4) from the first to the third trimester suggest the need for ongoing monitoring of thyroid function in pregnancy, consistent with guidelines recommending trimester-specific reference ranges and adjustments in levothyroxine dosage[13].

The high compliance rate with levothyroxine treatment observed in our study is encouraging, though the reasons for non-compliance highlighted the importance of addressing potential side effects and enhancing patient education to improve adherence[14].

This striking high incidence of abortions in women with thyroid dysfunction underscores the critical impact of thyroid health on pregnancy viability. Thyroid hormones play a vital role in early pregnancy, supporting embryogenesis and placental development[15]. Disruptions in thyroid function can lead to hormonal imbalances that compromise the uterine environment, potentially leading to increased risks of miscarriage or abortion[16]. The substantial increase in abortion rates among those with thyroid dysfunction in this study aligns with existing literature, which has consistently indicated that both overt and subclinical thyroid disorders are linked to higher miscarriage rates[17].

The findings from this study add to the growing body of evidence suggesting the need for vigilant monitoring and management of thyroid function in pregnant women. Early detection and treatment of thyroid dysfunction could be pivotal in reducing the risk of abortion, thereby improving pregnancy outcomes. This underscores the importance of thyroid screening as part of routine prenatal care, particularly for women with known risk factors for thyroid disorders[18].

Given the profound implications of thyroid dysfunction on pregnancy loss, future research should aim to further elucidate the mechanisms by which thyroid hormones influence early pregnancy. Additionally, randomized controlled trials are needed to evaluate the effectiveness of thyroid hormone therapy in preventing abortion in pregnant women with identified thyroid dysfunction. Such studies could provide the basis for revised clinical guidelines, potentially incorporating universal thyroid screening and early intervention strategies to mitigate the risks associated with thyroid dysfunction during pregnancy.

Limitations

This study's limitations include its observational design, which precludes causal inferences, and the potential for selection bias given the single-center setting. Additionally, the reliance on TSH and FT4 without routine measurement of triiodothyronine (T3) levels may have led to underdiagnosis of certain cases of hyperthyroidism.

Future Directions

Further research with larger, multicenter cohorts is necessary to validate our findings and explore the longitudinal impact of thyroid dysfunction on maternal and neonatal outcomes. Additionally, randomized controlled trials are needed to assess the efficacy of screening and treatment interventions for thyroid dysfunction in pregnant women.

The study demonstrated a 5.0% prevalence of thyroid dysfunction among pregnant women, closely aligning with but slightly higher than the expected global prevalence rates. Hypothyroidism and hyperthyroidism were observed at rates of 2.0% and 1.0%, respectively, which are consistent with the lower end of prevalence rates reported in the literature. The association between thyroid dysfunction and adverse obstetric outcomes, although not statistically significant in this study, suggests a potential trend that warrants further investigation with larger sample sizes. Significant risk factors identified for thyroid dysfunction included age over 30 years and a family history of thyroid disease, highlighting the importance of these factors in prenatal screening strategies. The study also underscored the necessity of continuous monitoring of thyroid function across all trimesters of pregnancy due to the observed worsening of thyroid function over time. The high compliance rate with treatment protocols, particularly with levothyroxine, points to the effectiveness of patient education and management strategies in this cohort.