A randomized control trial comparing the clinical outcome of thyroxine supplementation in thyroid peroxide antibody- negative cases in patients with subclinical hypothyroidism in pregnancy

ABSTRACT

Background:

A normal free thyroxine level in the presence of an increased thyroid-stimulating hormone is what constitutes subclinical hypothyroidism (TSH). Changes in thyroid physiology during pregnancy result in the normal TSH range being lower than non-pregnant. Subclinical thyroid disease during pregnancy is associated with adverse outcomes, including, risk of adverse pregnancy and neonatal outcomes. Prevalence in India is 6–8%. The prevalence of antibodies varies with ethnicity. Pregnancy with TSH concentrations >2.5 mIU/L needs evaluation for thyroid peroxidase antibody (TPO) antibody status. Literature and guidelines support Thyroxine supplementation in TPO antibody-positive patients and TPO-negative with TSH >10 mIU/L. However, there are numerous debates around pregnant individuals with TPO antibody negative and TSH <10 mIU/L.

Objective:

To determine the effect of thyroxine supplementation in pregnant women with TPO antibody-negative subclinical hypothyroidism. It is a prospective randomized control study conducted in the tertiary care institute of eastern India. In this trial, a TSH estimation of all pregnant women visiting the OPD of a tertiary care institute was performed. TSH values >2.5 are subjected to TPO antibody estimation. Patients with TSH value 2.5–5.0 mIU/L and TPO antibody negative were included. A total of 60 cases were included, randomized into two groups (Group A and B). Group A-thyroxine supplemented, Group B-placebo (folic acid). Thyroid levels are measured at intervals. Followed up for pregnancy, delivery, and neonatal complications. We studied the following outcomes: 1. Pregnancy-related complications – Gestational hypertension, gestational diabetes mellitus, and intrahepatic cholestasis of pregnancy (IHCP), intra-uterine growth retardation (IUGR), Antepartum hemorrhage (APH), oligohydramnios, and period of termination of pregnancy. 2. Delivery-related complications - mode of delivery, fetal distress, birth weight. 3. Neonatal Complications- Birth asphyxia, Neonatal Intensive Care Unit (NICU) admission, neonatal jaundice (hyperbillirubinaemia), Respiratory distress syndrome, Preterm birth, low birth weight (LBW), appearance, pulse, grimace, activity, and respiration score in 1 min and 5 mins, stillbirths (if any).

Results:

Group A-period of gestation (POG) at termination (36.99+/−2.70), more mean birth weight (2.8+/−0.424) P = 0.04, less NICU admission (P = 0.03). IUGR was less (P = 0.005). Hyperbilirubinemia was more common among group B (0.017), and term birth was more common in group A (0.046). LBW was higher among Group B (0.007).

Conclusion:

With thyroxine supplementation POG at termination, this study shows that mean birth weight was higher, NICU admissions were lower, and IUGR was lower. There was no discernible variation in other outcomes. Because this was a pilot study, the sample size was modest. Larger samples might be used in future studies.

Introduction

Subclinical hypothyroidism defined as raised TSH with normal fT4 is 6-8% more common than overt hypothyroidism during pregnancy in Asian nations.[1,2,3] Thyroid disorder during pregnancy can have an impact on the mother’s and child’s health both before and after delivery.[4] Uncorrected thyroid dysfunction during pregnancy has a negative impact on neuro-intellectual development in the child’s early years, in addition to pregnancy and delivery.[1,2,4]

Understanding the mechanism

The fetal thyroid gland becomes functional by 18–20 weeks of gestation. Before this, the fetus is completely dependent on maternal supplementation. Also, there is an increased requirement of iodine supplementation by the thyroid gland by 30% during the first trimester; hence, the World Health Organisation advises 250 micrograms of iodine per day during pregnancy to ensure optimal thyroid hormone synthesis.[1,5,6] During pregnancy, Placental human chorionic gonadotropin (hCG) stimulates thyroid hormone secretion, often decreasing maternal thyrotropin (TSH) concentrations. Thyroxine (T4) levels rise gradually over 6-12 weeks and peak in mid-gestation, with varying TSH levels in the contrary pattern.[7] Also, estrogen increases in thyroid hormone binding proteins, which causes an increase in total thyroid hormone (TSH) levels, but Ft4 hormone (the quantity that is not bound and may be used) normally remains normal. The thyroid is working correctly if TSH and Free T4 levels remain within trimester-specific normal norms throughout pregnancy.[5]

Knowing our guidelines

According to American Thyroid Association (ATA), 2011, the normal range of TSH during pregnancy was defined as an upper limit of 2.5 mIU/L in the first trimester and 3.0 mIU/L in the second and third trimesters.[8] In 2017, the normal range was recommended as the TSH reference range of 0.1 to 4.0 mIU/L during the first trimester with a gradual return of TSH towards the non-pregnant normal range during the second and third trimesters.[1] However, the recommendation also states that subclinical hypothyroidism should be treated in females with positive thyroid peroxidase antibody (TPO) antibodies and TSH greater than 2.5 mIU/ml, and evaluation of thyroid peroxidase antibody status is recommended with TSH concentrations >2.5mIU/L.[1] Also, the ETA guideline, 2013, says subclinical hypothyroidism (SCH) is generally classified into two categories according to serum TSH level: mildly increased TSH levels (4.0–10.0 mIU/L) and more severely increased serum TSH concentrations (>10.0 mIU/L).[9]

Among subclinical hypothyroidism, 4.3% of persons with detectable antibodies against thyroid peroxidase (TPO), and 2.6% of those with no detectable antibodies convert into overt hypothyroidism over years.[10] TSH levels above 10 mIU/L indicate a faster rate of progression, while levels below 6 mIU/L indicate a lesser risk of progression to overt.[11] Transiently suppressed maternal TSH concentrations are often observed and deemed safe, defining the upper reference limit for serum TSH in this population has remained controversial.[1] Association with undesirable results in pregnancy has remained inconsistent, emphasizing additional research to conclude the need of required treatment.[12] When possible, population-based trimester-specific reference ranges for serum TSH should be defined through assessment of local population data representative of health care providers. Anti-TPO or anti-thyroglobulin autoantibodies are present in 2%–17% of unselected pregnant women.[13] The prevalence of antibodies varies with ethnicity. Most of the literature and guidelines support Thyroxine supplementation in TPO Ab-positive patients and TPO-negative with TSH >10 mIU/L. Controversies remain in the treatment of patients with TPO Ab negative with TSH 2.5–5 mIU/L is concerned. Hence, we conducted this study.

Methodology

This was a prospective randomized control trial conducted in a tertiary care center of Eastern India catering to semi-urban population, for which approval by the institutional ethics committee was taken (IEC 67). Trial was registered in clinical trial registry of India (CTRI/2016/08/007181). This research did not receive any specific grants from funding in the public, commercial, or non-profit sectors.

Our pilot study was a single-blinded randomized control study. The study population was all pregnant women attending antenatal OPD. It was conducted for one year.

As an institutional protocol, thyroid stimulating hormone (TSH) estimation of all pregnant women attending antenatal OPD was evaluated for TSH, and women with a TSH value of 2.5 or above are subjected to thyroid peroxidase antibody (TPO) estimation. Patients with TSH values between 2.5 and 5.0 mIU/L and TPO antibody negative were included in the present study after obtaining written informed consent.

Participants were categorized into the following categories based on their previous thyroid history and current thyroid function test results:

Hypothyroidism: Serum-free thyroxine (FT4) <0.89 ng/dL and thyroid stimulation hormone (TSH) >5.50 μIU/L. Hyperthyroidism: FT4 >1.76 ng/dL and TSH <0.35 μIU/L. Subclinical hypothyroidism: normal serum FT4 and TSH >5.50 μIU/L. Subclinical hyperthyroidism: normal serum FT4 and TSH levels of <0.35 μIU/L on levothyroxine. Undetected Hypothyroidism: Subjects without a history of hypothyroidism were found to have hypothyroidism via thyroid function tests. Anti-TPO antibody positive: Anti-TPO antibodies greater than 35 IU/mL.

In this study, all enrolled TPO-negative patients following informed consent, were randomized into two groups using a computer-generated sequence.

Group – A received thyroxine supplementation as per standard institutional protocol

Group – B received placebo treatment in the form of folic acid tablet.

Repeat TSH testing was done 6 weeks later, then at 24–26 weeks and at 32 weeks and just before delivery (as per ATA guidelines). Patients not fulfilling the inclusion criteria were excluded from the study. Patients were followed and pregnancy, delivery and neonatal outcomes were noted as follows:

Pregnancy-related complications

Gestational hypertension, gestational diabetes mellitus, intra hepatic cholestasis of pregnancy (IHCP), intra-uterine growth retardation (IUGR), Ante partum haemorrhage (APH), oligohydramnios, period of termination of pregnancy.

Delivery related complications

Mode of delivery, fetal distress, birth weight.

Neonatal complications

Birth asphyxia, Neonatal Intensive Care Unit (NICU) admission, neonatal jaundice (hyperbillirubinaemia), Respiratory distress syndrome (RDS), Preterm birth, low birth weight (LBW), appearance, pulse, grimace, activity, and respiration (APGAR) score in 1 min and 5 mins, still births (if any).

Sample size

Since it was a pilot study, a total of 60 patients were taken depending on patients attending in Gynecology and obstetrics OPD of Tertiary care institute of Eastern India [Figure 1].

Figure 1.

Flow chart showing study methodology

Inclusion criteria

All pregnant women who attended our antenatal OPD with TSH value >2.5–5 mIU/L with negative status for TPO antibodies in their 1^st trimester.

Exclusion criteria

Patients with previous bad obstetric history. Patients with TSH >5 mIU/L irrespective of TPO antibody status. Patients with TSH <0.1 mIU/L or >5 mIU/L anytime during the study. Patients who failed to give consent

Statistical analysis

All analysis was conducted using the data were entered and analyzed into IBM Corp. Released 2013. IBM SPSS Statistics for Windows, Version 22.0 (IBM Corp., Armonk, NY). Normality of data checked by Q-Q plot, there were 4 outliers in placebo, 2 in treatment group. In period of gestation (POG) (at time of delivery) there was 1 extra outlier. 3 outliers in placebo group, 2 outliers in treatment group, which were included in study. Baby weight- 2 outlier, 1 in treatment group.

Means were compared with independent t test, there were no significant difference found in age. P value calculated using chi square test, Fischer exact test was calculated for an expected count of the cell n <5 (significant if P < 0.05).

Results

In the group of patients receiving placebo, approximately 50% experienced an incidence of Intrauterine Growth Restriction (IUGR), with 10 out of 20 babies of individuals being affected. In cases of subclinical hypothyroidism where placebo was administered, various neonatal complications were observed at the following rates: hyperbilirubinemia occurred in around 33.33% (10 out of 30), LBW was evident in approximately 53.33% (16 out of 30), preterm delivery occurred at a rate of approximately 33.33% (10 out of 30), and NICU admissions were required for roughly 60% (18 out of 30) of neonates where placebo was given antenatally instead of thyroxine. Period of gestation at termination is found to be less in placebo group (36.99 ± 2.70) while mean birth weight (2.8 ± 0.424) is more in those where thyroxine was given early in pregnancy.

The Table 1 compares patient demographics and obstetric factors between Placebo (N = 30) and Thyroxin (N = 27) groups. It shows age, education, residence, parity distribution and it shows no significant difference between two groups.

Table 1.

Comparison of patient’s demographic profile and obstetric parameters among the groups

Parameter		Placebo (n=30)	Thyroxin (n=27)	t (df)	P
Mean age (years)		25.03±4.45	24.11±3.54	0.859 (55)	0.39
Education	Illiterate	1 (50%)	01 (50%)	1.406 (3)	0.802
	Primary	6 (40%)	09 (60%)
	Secondary	14 (56%)	11 (44%)
	Graduate & above	09 (60%)	06 (40%)
Residence	Rural	18 (58.1%)	13 (41.9%)	0.805 (1)	0.802
	Urban	12 (46.2%)	14 (53.8%)
Parity	Primi	10 (52.6%)	47.4%)	0.06 (1)	1.0
	Multi	20 (52.6%)	18 (47.4%)

The Table 2 presents a comparison of pregnancy-related complications between the Placebo (N = 30) and Thyroxin (N = 27) groups. It lists occurrences of complications such as Gestational Hypertension, GDM, IHCP, IUGR, APH, and Oligohydramnios. The Chi-square tests examine the association between these complications and the two groups. Notably, the Thyroxin group displayed fewer cases of IUGR compared to the Placebo group, with a statistically significant difference. The groups also differed significantly in terms of POG, where the Thyroxin group had a slightly higher mean POG at termination compared to the Placebo group.

Table 2.

Comparison of pregnancy related complications among two groups

Pregnancy related complications		Placebo (n=30)	Thyroxin (n=27)	χ2 (df); P
Gestational Hypertension	No	25	23	0.037 (1); 1.00
	Yes	05	04
Gestational Diabetes Mellitus	No	28	24	0.351 (1); 0.660
	Yes	02	03
IHCP	No	25	23	0.037 (1); 1.00
	Yes	05	04
IUGR	No	20	26	8.01 (1); 0.005
	Yes	10	01
APH	No	28	27	1.865 (1); 0.492
	Yes	02	00
Oligohydramnios	No	27	25	0.119 (1); 1.00
	Yes	03	02
POG at termination (weeks)		36.99±2.70	38.23±1.48	2.108 (55); 0.040

IHCP: Intrahepatic cholestasis of pregnancy, POG: Period of gestation, APH: Antepartum hemorrhage, IUGR: Intrauterine growth retardation

The Table 3 compares delivery-related complications between the Placebo and Thyroxin groups. It highlights the Mode of Delivery (Vaginal vs. LSCS - Lower Segment Cesarean Section) percentages, revealing no significant difference in delivery method distribution between the two groups. The mean Birth Weight (kg) is also presented, with the Thyroxin group exhibiting a significantly higher birth weight compared to the Placebo group. This suggests that Thyroxin might be associated with improved fetal growth. The Chi-square tests indicate no significant differences in mode of delivery, while the birth weight shows a statistically significant difference between the groups.

Table 3.

Comparison of delivery related complications among two groups

Delivery related complications		Placebo	Thyroxin	χ2(df)	P
Mode of delivery	Vaginal	08 (44.4%)	10 (55.6%)	0.707 (1)	0.569
	LSCS	22 (56.4%)	17 (43.6%)
Mean Birth wt.(kg)		2.37±0.680	2.8±0.424	3.017 (55)	0.004

LSCS=Lower segment cesarean section

The Table 4 compares neonatal complications between the Placebo and Thyroxin groups. It includes occurrences of Hyperbilirubinemia, RDS, Sepsis, Birth Asphyxia, Preterm Birth, LBW, APGAR scores at 1 and 5 min, and NICU admission. Hyperbilirubinemia, Preterm Birth, NICU admission and LBW showed significant differences between groups. Other complications displayed no significant differences. The APGAR scores demonstrated no significant variations. Overall, Thyroxin usage might contribute to reduced Hyperbilirubinemia, preterm births, NICU admission and LBW, suggesting potential benefits in neonatal health. Consort in the form of flow chart of study participants with that of significant findings in the study [Figure 2].

Table 4.

Comparison of neonatal complications among two groups

Neonatal complications		Placebo	Thyroxin	χ 2	P
Hyper-bilirubinemia	No	20	25	5.747	0.017
	Yes	10	02
Respiratory Distress	No	29	27	0.916	1.00
	Yes	01	00
Sepsis	No	27	25	0.119	1.00
	Yes	03	02
Birth Asphyxia	No	29	27	0.916	1.00
	Yes	01	02
Delivery	Preterm	10	3	3.98	0.046
	Term	20	24
Low-birth weight (Kg)	<2.5	16	05	7.402	0.007
	>=2.5	14	22
Apgar score@ 1 min.	<7	02	01	0.250	0.617
	>=7	28	26
APGAR score@ 5 min.	<7	01	00	0.916	0.339
	>=7	29	27
NICU admission	No	18 (43.9%)	23 (56.1%)	4.46 (1)	0.035
	Yes	12 (75%)	04 (25%)

NICU=Neonatal intensive care unit, APGAR: Appearance, pulse, grimace, activity, and respiration

Figure 2.

Flow chart of study participants with that of significant findings in the study

Discussion

Numerous physiological changes take place during pregnancy in both the mother and the fetus. As part of physiology, production of thyroid hormones and the need for iodine both rise by about 50% during pregnancy.[14] Endocrine abnormalities like hypothyroidism during pregnancy can have severe negative effects on both the mother and the fetus. Hypothyroidism is present in about 2.5% of pregnant women.[8] There are a few papers from India describing the prevalence of hypothyroidism during pregnancy, with percentages ranging from 4.8% to 11%.[15] Untreated hypothyroidism from birth has a substantial impact on a child’s intellectual growth.[15] Hypothyroidism leads to severe neurological consequences.[15] In a community-based large-scale study involving over 500,000 pregnant women from the USA showed a 15.5% prevalence of hypothyroidism. Hypothyroidism was found in 7 (4.12%) women with recurrent pregnancy loss and one in the control group. The study demonstrates that hypothyroidism has a statistically significant relation with pregnancy loss in the first trimester.[16] One of the study included 500 pregnant women attending two Government Obstetrics and Gynecology Hospitals in Chennai for a period of five months in 2007 for thyroid function. Subclinical hypothyroidism was detected in 2.8%, among them, TPO antibodies positivity was seen in 57.1%, whereas euthyroid women had significantly lower positivity (7%).[17] The impact of thyroid dysfunction on pregnancy outcomes appears to manifest with a TSH threshold of >2.5 mIU/L in the first trimester rather than with a TSH range based on percentiles cutoff derived from apparently “normal” pregnant women. ATA recommends >2.5 and >3.0 μIU/ml for the diagnosis of hypothyroidism during the first and later part of pregnancy, respectively.[18]

We have found in our study that the Thyroxin group displayed fewer cases of IUGR compared to the Placebo group, with a statistically significant (P value = 0.005) difference. In another study by Roushali et al. involved 300 patients with a follow-up up to 12 weeks post-partum, observed subclinical hypothyroidism prevalence 6.47-9% with adverse neonatal outcomes of low and very low birth weight, low Apgar scores, respiratory distress syndrome, and meconium aspiration syndrome. The findings revealed a significantly higher rate of IUGR in the cases compared to the controls, indicating a connection between subclinical hypothyroidism and an increased risk of IUGR, like our study.[19] In another study by S. Hebbar et al.[20] there is 1.3% risk of IUGR in patients with subclinical hypothyroidism.

In our study the groups also differed significantly in terms of period of gestation at Termination (POG), where the Thyroxin group had a slightly higher mean POG at termination (P value- 0.040) compared to the Placebo group. Thyroxin group also showed a lower chance of preterm deliveries with significant P value (P value = 0.046). Similarly in another study by Shaowei Wang et al.[21] through a random effects analysis, it was determined that pregnant women with subclinical hypothyroidism had a greater likelihood of experiencing preterm birth compared to the control group. The odds ratio (OR) was 1.25, with a 95% confidence interval (CI) of 1.14–1.36, and the result was statistically significant with a P value less than 0.01. Study by Hebbar et al.[20] showed that preterm delivery is significantly associated with subclinical hypothyroidism. Another study by A. Pavanaganga et al.[22] showed that there is 7.1% chance of preterm labour in women with subclinical hypothyroidism.

In the present study the mean birth weight (kg) is also presented, with the Thyroxin group exhibiting a significantly higher (P value = 0.004) birth weight compared to the Placebo group. This suggests that Thyroxin might be associated with improved fetal growth. Similarly significant number of LBW babies was born to patients in placebo group (P value = 0.007). Similarly, Arash Derakhshan et al.[23] described in his study that subclinical hypothyroidism was associated with a lower mean birth weight, with an adjusted risk difference of −38 g (95% CI −61 to −15), and a P value of 0.001. As stated by Uma Ram et al.[24] that subclinical hypothyroidism who were treated as lower chance of developing LBW.

In our study there is increased chance of hyperbillirubinaemia among the patients in placebo group (P value = 0.017). Similarly, in a study conducted by Budhhi Gunasekara et al.[25] he found that babies born to hypothyroid women had 18% chance of developing jaundice. A study conducted by Dr Majnu V et al.[26] she concluded that in her study major complications observed in pregnant females with subclinical hypothyroidism was neonatal jaundice (NNJ) 20.7%.

In this study we have found that in the Placebo group, 43.9% of neonates did not require NICU admission, while 75% of neonates in the Thyroxin group did not require NICU admission. This indicates that a higher proportion of neonates in the Thyroxin group experienced reduced NICU admission compared to the Placebo group. The statistical analysis with a Chi-square test yields a significant difference (P = 0.035), highlighting the potential beneficial impact of Thyroxin on reducing the need for NICU care in newborns secondary to LBW and hyperbiliruinemia. Similarly in one study by Tuijja et al.[27] infants born to mothers with hypothyroidism had a higher likelihood of requiring NICU care. Another study by DK Dhanwal et al.[18] stated that there is increased chance of ICU admission among pregnant women with subclinical hypothyroidism than normal pregnancy. A similar association was seen in the study conducted by Bilal Ur Rehman et al.[28] there was a notable increase in NICU admissions for infants born to Subclinical Hypothyroidism (SCH) patients compared to pregnant women with normal thyroid function. Taken together in our study complications like IUGR, hyperbilirubinemia, LBW, pre term delivery, NICU admission are less in group supplemented with thyroxine. Table 5 compares complications observed in different studies with untreated subclinical hypothyroidism. Thus, early administration of levothyroxine in subclinical hypothyroidism, improves both neonatal as well as obstetric outcome. Subclinical hypothyroidism- TSH >2.5 mU/L – needs treatment. As our study was conducted on a small group of patients, further studies involving large group are needed to reveal more of such associations.

Table 5.

Comparative illustration of complications seen in subclinical hypothyroidism when not treated

Complications	Hebbar et al.[20]	Gunasekara et al.[25]	Rehman et al.[28]	Our study
Pre-eclampsia	3.8%	10%	35%	14%
Preterm	7.6%	7%	20%	33.33%
Low birth weight	3.8%	11%	33.9%	53%
NICU admission			66.7%	75%
Apgar score	2.5%		62.5%
Hyperbilirubinemia		18%		33.33%

Conclusion

Collectively, our research findings reveal that the incidence of complications of fetal growth restriction (IUGR), hyperbilirubinemia, low birth weight, preterm delivery, and NICU admissions was notably reduced among those who received thyroxine supplementation. This suggests that early administration of levothyroxine in cases of subclinical hypothyroidism yields improved outcomes for both neonates and obstetric conditions even in TPO antibody negative status encouraging treatment in pregnancy with subclinical hypothyroidism. Though the results are significant, it’s crucial to acknowledge that our study was conducted with a limited number of participants. Therefore, further research involving larger and more diverse groups of patients is necessary to uncover more comprehensive insights into these associations.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

No funding was received to assist with the preparation of this manuscript.