Prevalence of Thyroid Disorders among Pregnant and Non-Pregnant Women Attending a Tertiary Care Center in Kathmandu

Thyroid hormones are crucial for the overall development of the fetus, and their impact on the pregnancy outcomes needs to be considered seriously. Hence, universal screening for thyroid disorders is recommended in the first trimester of pregnancy. One hundred pregnant women in their first trimester and 100 non-pregnant women of the reproductive age group were screened for thyroid function test. The prevalence of thyroid disorders among the total participants was 32.0% of which 23.5% were hypothyroid and 8.5% were hyperthyroid. Pregnant females had a significantly higher prevalence of thyroid disorders (46.0%) than non-pregnant counterparts (18.0%; P <0.001). Pregnant females had significantly higher odds of hypothyroid disorders than non-pregnant females (OR 3.95; P <0.001). The prevalence of subclinical hypothyroidism among pregnant and non-pregnant was 34.0% and 12.0% respectively which makes it the most common thyroid disorder in both study groups. The median values of FT3, FT4, and TSH levels were, however, not significantly different between the study groups. After adjusting for the confounding effect of age, the odds of thyroid disorders were still significantly higher in pregnant women than in non-pregnant (p =0.001). The prevalence of thyroid disorders, specifically hypothyroidism, is higher in pregnant women compared to non-pregnant counterparts. And this emphasizes on the need of antenatal thyroid screening to be made mandatory in the health policy.


INTRODUCTION
Thyroid hormones are crucial for the overall development of the fetus, and their impact on the pregnancy outcomes needs to be considered seriously. 1,2Various physiological changes like increased thyroid hormone-binding globulin concentration, increased iodine clearance in the kidneys, and thyrotropic effect of human chorionic gonadotropin etc. happening during pregnancy might lead to alteration in thyroid functions which are associated with an increased risk of miscarriage, placental abruption, preterm delivery, preeclampsia, and physical and mental growth restriction in fetus, if timely treatment is not sought. 3Assessment of thyroid function during pregnancy is essential for both maternal and fetal health outcomes.Hence, universal screening for thyroid disorders is recommended in the first trimester of pregnancy. 4Data shows at least 2.0% -3.0% of women of the reproductive age group are affected by thyroid problem, 5 making it the second most common endocrine disorders seen in pregnant women. 6thyroid screening or thyroid function test (TFT) is a blood test that includes thyroid stimulating hormone (TSH), free thyroxine (FT 4 ), and free triiodothyronine (FT 3 ).Thyroid antibody tests like anti-thyroid peroxidase may also be done if required. 7Thyroid disorders can be categorized into hypothyroidism and hyperthyroidism. 8Several studies show the prevalence of thyroid disorders to range from 2.8% to 18.7% amongst the Indian pregnant population. 9,10The prevalence of 24.0%, 29.0% and 39.5% were reported by different studies conducted in Kathmandu. 11-13Also, one study from Western Nepal has reported the prevalence of hypothyroidism to be 44.0%. 14hese data show the higher prevalence of thyroid disorders among pregnant women in Nepal compared to India.However, such studies, especially comparative studies, from Nepal are not available.Also, the data on the burden of thyroid disorders among the Nepalese pregnant women is not well established.This study aims to study the prevalence of thyroid disorders in pregnant women as compared to non-pregnant females of reproductive agegroup.Study participants were divided into two groups: pregnant and non-pregnant.One hundred pregnant women of 18-49 years, in their first trimester coming for antenatal checkups were selected irrespective of their gravida status (primigravida or multigravida) and parity.Apparently healthy 100 non-pregnant women of the similar age group visiting NMCTH laboratory for routine examination were counseled for TFT.Informed verbal and written consent was taken from both the groups prior to the study.Socio-demographic and medical history were recorded, and those with previous history of thyroid dysfunction and or under medication for it were excluded.A convenience sampling technique was used for selection of participants and the sample size was calculated using following formula: N = z 2 pq/d 2 All the participants were screened for TFT which was done using enhanced chemiluminescence immunoassay (ECLIA) in the laboratory of NMCTH.The reference range used in the study was based on the guidelines of the American Thyroid Association (ATA) 2017 according to which the upper limit of TSH should be 2.5 μIU/L in the first trimester, and 3.0 μIU/L in the second and third trimesters. 15The reference range for TFT parameters used for the nonpregnant women according to the laboratory of NMCTH was: FT 3 : 2.77-5.27pg/ml, FT 4 : 0.78-2.19ng/dl and TSH: 0.465-4.68μIU/ml.

Materials and Methods
According to the ATA guidelines, pregnant women will be classified into five groups: 15  Data was analyzed using SPSS-16.Normality distribution of the variables were tested.Accordingly, continuous data were expressed as median (IQR) and categorical data as counts (percentages).Prevalence of thyroid disorders along with their 95.0%confidence interval (CI) were calculated.Odds ratio for hypothyroidism, hyperthyroidism, and thyroid disorders were calculated.Mann-Whitney U test, Chi-square analysis, and binary logistic regression analysis were performed.P value of less than 0.05 was considered as statistically significant at 95.0% confidence intervals.

RESULTS
A total of 200 participants within 18-49 years were recruited in the study of which 100 were pregnant and 100 were non-pregnant.The median age of the participants was 30 years.Pokhrel et al and Chaudhary et al 16 conducted in eastern Nepal, documented prevalence rates of 44.0% and 20.6%, respectively.Possible explanations for these variations include geographical distinctions between central, western, and eastern Nepal, also the dietary differences and the implementation of different upper limit cutoff values for TSH.The notable difference in thyroid disorder rates between pregnant and non-pregnant females in our study may also be attributed to the utilization of trimesterspecific TSH cutoff values for pregnant women and laboratory-specific TSH cutoff values for non-pregnant women.
and Gupta et al 24 observed prevalence rates of 2.0%, 1.5%, and 3.1%, respectively, for subclinical hyperthyroidism among the pregnant Indian population in their respective studies.The observed discrepancies may also be attributed to the diverse cut-off values for TSH in diagnosing hyperthyroidism, as previously mentioned.Presently, there is no established association between subclinical hyperthyroidism and pregnancy outcomes, and therefore, the identification and treatment of this condition during pregnancy are not considered necessary. 25 our study, the odds of thyroid disorders were significantly high in pregnant females compared to non-pregnant counterparts (adjusted OR 3.21; p =0.001).This was especially evident for hypothyroid disorders (OR =3.95; P =0.0002).These results strongly support and advocate for the importance of screening for thyroid dysfunction during early pregnancy.However, thyroid disease can equally affect women either before, during, or immediately after pregnancy.Moreover, careful consideration of TSH cut-off levels seems to be essential in the analysis and interpretation of the data.
This remarkably high prevalence of thyroid disorders among the Nepalese pregnant women compared to the previous studies and worldwide prevalence points towards the 12. Shrestha B, Adhikari P. Screening of thyroid disorder among pregnant ladies in a tertiary urgent need of TFT screening policies to be made mandatory during antenatal visits in all the health care set ups of Nepal.Also, the need to establish nationwide or region-specific TSH cut-off ranges, especially for pregnant women cannot be underscored.This could be an area that requires further investigation.

LIMITATIONS:
As this is a single center hospital based study conducted in a small sample, it may not represent the general population.

Fig. 1 :
Fig. 1: Frequency distribution of sub-clinical and overt thyroid disorders

table 2 .
The prevalence of SCH among pregnant and non-pregnant women was 34% and 12 % respectively.The sub-group wise distribution of thyroid disorders is shown in figure1.The median values of FT 3 , FT 4 , and TSH levels were, however, not significantly different between the study groups (table3).

Table 2 : Prevalence of hypothyroid and hyperthyroid disorders along with their OR
13A = Not applicable.P <0.05 considered statistically significant13Other studies conducted by Shrestha et al 11 and Khakurel et al. 12 in tertiary care centers in Kathmandu reported a slightly lower prevalence of 29% and 24.62% for thyroid disorders respectively.11,12 Additional studies by Upadhyaya et al 14 conducted in western Nepal

Table 4 : Unadjusted and adjusted odds ratio of thyroid disorders between study groups Coefficient (β) Unadjusted Odds Ratio Adjusted Odds Ratio OR P -value OR (exp β) P -value
Adjusted OR and P-values from binary logistic regression analysis.Dependent variable = Thyroid status (Euthyroid/ Thyroid disorder); Independent Variable = Pregnancy status (Pregnant/non-pregnant). OR and P-value adjusted for age as participants ages were significantly different between the study group (See table 3).
Gayathri et al 9 found a 2.8% prevalence of hypothyroidism among pregnant women in Chennai, whereas Sahu et al 17 reported that 11.0% of pregnant women had hypothyroidism (6.5% SCH and 4.6% OH).