|Year : 2013 | Volume
| Issue : 4 | Page : 18-19
Thyroid disease in pregnancy: Experience from a large Indian cohort
Dinesh K Dhanwal
Department of Medicine and Endocrinology, Maulana Azad Medical College, New Delhi, India
|Date of Web Publication||2-Feb-2013|
Dinesh K Dhanwal
Department of Medicine and Endocrinology, Maulana Azad Medical College, New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Dhanwal DK. Thyroid disease in pregnancy: Experience from a large Indian cohort. Thyroid Res Pract 2013;10, Suppl S1:18-9
| Introduction|| |
Hypothyroidism during pregnancy is deleterious to both mother and her child. Children born to untreated or under treated mothers have profound effect on future intellectual development. Pregnancy has a profound impact on the thyroid gland and thyroid function. During pregnancy, the thyroid gland may enlarge by 10% in countries where iodine sources are sufficient and to a greater extent in iodine-poor countries. Production of thyroid hormones and iodine requirement each increases by approximately 50% during pregnancy. Pregnancy is a stress test for the thyroid, resulting in hypothyroidism in women with limited thyroidal reserve or iodine deficiency.
What should be the normal upper limit of thyroid stimulating hormone (TSH) in pregnancy? This has been debated for a long time and the established upper limit of TSH is 2.5 uIU/l. Recent guidelines proposed by National Association of Clinical Biochemistry (NACB) state that the upper limit of serum TSH euthyroid reference range should be reduced to 2.5 mIU/L for pregnant women, because >95% of rigorously screened normal euthyroid volunteers have serum TSH values between 0.4 and 2.5 mIU/L. However, the American Association of Clinical Endocrinologists (AACE) and The Endocrine Society (TES) consensus panel continues to recommend that 4.5 mIU/L should be maintained as the upper limit of normal level, reasoning that although some individuals within the range of 2.6-4.5 mIU/L may have subclinical thyroid disease, there is a lack of evidence of adverse outcome in this group. This was supported by a recent study from Reh et al. in a large cohort of first cycle in vitro fertilisation (IVF) patients from 2005 through 2008. Although lowering the TSH threshold to 2.5 mIU/L would result in a nearly five-fold increase in the number of women being classified as hypothyroid, the lack of differences in maternal clinical outcomes must be considered in the current controversy regarding the relative merits of lowering the upper limit of normal TSH. Therefore, for the present study, we have set upper limit of TSH as 4.5 uIU/l. Another confounding factor that affects thyroid function during pregnancy is human chorionic gonadotropin (hCG), a key pregnancy hormone having thyromimetic actions. Clinically, hCG levels peak between 6 and 12 weeks of pregnancy, which correlates with reduced TSH level and hyperemesis gravidarum. This action of hCG by cross-reactivity of this hormone with TSH receptors.
Data from recently published studies have underscored the association between miscarriage and preterm delivery in women with normal thyroid function who test positive for thyroid peroxidase antibodies. Prenatal and postnatal adverse effects including attention deficit and hyperactivity syndrome have been reported in children born to hypothyroid mothers. During the first trimester, approximately 1 in 10 pregnant women develops antibodies to thermoplastic polyolefin (TPO) or to thyroglobulin, and hypothyroidism develops in roughly 16% of these women. The prevalence of hypothyroidism in pregnancy is around 2.5% according to the Western literature. There are few reports of prevalence of hypothyroidism during pregnancy from India with prevalence rates ranging from 4.8% to 11%. In a recently concluded prospective study, a total of 1000 pregnant women were enrolled during their first trimester [Table 1]. The mean (standard deviation, SD) age of study subjects was 25.6 (11.1) and mean (SD) gestational age was 10.3 (3.4) weeks. One hundred and forty three (14.3%) subjects had TSH values >4.5 uIU/L above the cut-off value used for definition of hypothyroidism. Hypothyroidism, especially subclinical, is common in north Indian women during the first trimester.
To assess the status of thyroid function during pregnancy, we concluded a country wide study (India Thyroid Project) and enrolled 3064 pregnant women in it. The study was carried out at Kolkata, Chennai, Vizag, Pune, Nasik, Rohtak, Delhi, Allahabad, Bangalore, Hyderabad, and Srinagar. All patients were subjected to detailed history and clinical examination using a pre-designed proforma. Blood samples were collected in out-patient department (OPD) setting between 0800 and 1100 hours. The serum urea, creatinine, bilirubin, aspartate aminotransferase, and alanine aminotransferase levels were checked to assess liver and renal function using standard auto analysers. Complete blood counts and lipid profile were also estimated. Estimation of free T3, free T4, and TSH were carried out using Advia Centaur XL Siemens kit dedicated equipment using CLIA technique, and anti-TPO was carried out by using Hycor kits by ELISA method in a NABL accredited lab. The intra assay variability of free T4, free T3, TSH, and anti-TPO was 3.0, 2.4, 3.4, and 4.2%, respectively, and inter assay variability for these parameters was 4.7, 2.7, 3.1, and 2.2%, respectively. Of 3064 pregnant women, 396 had TSH values >4.5 uIU/L, suggesting that 12.9% of pregnant women in India have hypothyroidism. Detailed analysis of this study will be presented during ITSCON 2013.
To conclude, thyroid dysfunction, especially hypothyroidism, is an important health problem during pregnancy. Indian specific guidelines need to be evolved based on India Thyroid Project results. Early diagnosis and treatment of hypothyroidism during pregnancy will help reduce maternal and foetal morbidity.
| Acknowledgment|| |
List of investigators: Dr. Dinesh Dhanwal, Dr. Usha Sriram, Dr. Sarita Bajaj, Dr. Mala Dharamlinga, Dr. Rakesh Sahay, Dr. Sudhankar Chaudhary, Dr. Ashraf Ganie, Dr. Rajender Bhandari, Dr. K.A.V. Subhramaiyam, Dr. Rajesh Rajpoot, and Dr. Narender Kotwal
| Suggested Readings|| |
- Dhanwal DK, Prasad S, Agarwal AK, Banerjee AK. High prevalence of subclinical hypothyroidism during first trimester of pregnancy in North India. Accepted for IJEM.
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