Early or relapsing Grave's Iodine deficiency Solitary nodule High Hashimotos Graves Molar pregnancy Choriocarcinoma Hyperemesis Thyrotoxicosis factitia Lithium Multinodular goiter Toxic adenoma Thyroid carcinoma Iodine ingestion Normal Low Hypothyroxinemia Severe nonthyroidal illness (euthyroid sick syndrome) Possible secondary hypothyroidism Medications Normal High Euthyroid hyperthyroxinemia Thyroid hormone resistance Familial dysalbumineic hyperthyroxinemia Meds: amiodarone, beta-blockers Oral contrast Hyperemesis.Thyroid function tests in pregnancy It is essential therefore to have reliable accurate tests of thyroid function in pregnancy as maternal thyroid dysfunction may affect maternal health, foetal health and obstetric outcome.
These changes are particularly pronounced in patients with hyperemesis gravidarum where FT4 levels may reach 37.6 and TSH may be supressed to undetectable levels 13 A suppressed TSH with normal FT4 and FT3 can usually be observed with repeat laboratories q 4 weeks until it normalizes 11.Brent GA. Maternal Thyroid function: Interpretation of thyroid function tests in pregnancy. Clin Obstet Gynecol. 1997;. 12. Mori M, et rning sickness and thyroid function in normal pregnancy. Obstet Gynecol. 1988 Sep;72(3 Pt 1 355-9.
Glinoer D et al. Regulation of maternal thyroid function during pregnancy. J Clin Endocrinol Metab 1990;. 2. Kol S, et al.Thyroid function in early normal pregnancy: transient suppression of thyroid-stimulating hormone and stimulation of triiodothyronine.Assays employing total T4 show a result approximately 1.5 times the non-pregnant value. There is general consensus that there is a transient rise in FT4 in the first trimester due to the relatively high circulating human chorionic gonadotrophin (hCG) concentration and a decrease of FT4 in the second and third trimester albeit within the normal.
Later in gestation (from about 16 weeks on) TSH is more reflective of thyroid status. Although the measurement of thyroid antibodies (thyroid peroxidize antibodies, TPOA bs and TSH receptor antibodies, TSHRA bs) does not give any indication of thyroid status, their presence does have important implications for the pregnancy.Pregnancy Serum Units first trimester second trimester third trimester Reference Free T3 pmol/L 3 - 5.7 2.8 - 4.2 2.4 - 4.1 15 Free T4 ng/dL 0.86 - 1.87 0.64 - 1.92 0.64 - 1.92 16 pmol/L 11.1 - 24.1 8.2 - 24.7 8.2 - 24.7 15 ng/dL 0.86 - 1.77 0.63 - 1.29 0.66.
Pregnancy Trimester Three: 6.3 to 9.7 g/dL or 81 to 125 nmol/L Laboratory Values During Pregnancy.Patients on levothyroxine require an increase in dosage during gestation. Areas of controversy are the following: total thyroxine (TT4) versus Free T4 (FT4) assays in pregnancy. Screening for thyroid function in early gestation: should it be routinely performed on everyone?
The resin is counted for labeled T3. The value is usually reported as a percent of the total labeled hormone added. A low resin uptake means that most of the labeled T3 has been taken up by serum proteins.When a total thyroxine blood test is ordered, the ordering physician will also order a free thyroxine and thyroid stimulating hormone test along with other blood tests. If a thyroid stimulating hormone (TSH) test was run earlier and an abnormal result was measured, the doctor may order a total thyroxine and free thyroxine test as.
2 Uncorrected thyroid dysfunction in pregnancy has adverse effects on foetal and maternal well-being. The deleterious effects of thyroid dysfunction also extend beyond pregnancy and delivery to affect neurointellectual development in the early life of the child.J Clin Endocrinol Metab 1993;. 6. Nohr SB et al. Postpartum thyroid dysfunction in pregnant thyroid peroxidase antibody-positive women living in an area with mild to moderate iodine deficiency: Is iodine supplementation safe?
The placenta secretes hCG, a glycoprotein hormone sharing a common alpha subunit with TSH but having a unique beta subunit, which confers specificity. hCG, or a molecular variant, acts as a TSH agonist so that elevated levels contribute to the cause of gestational transient hyperthyroxinaemia seen in about 0.3 of pregnancies.1 In iodine deficient areas, hypothyroxinaemia with preferential T3 secretion may occur accompanied by a rise in median TSH and serum thyroglobulin (Fig. 1 ). View larger version: Fig. 1 Gestational variation in thyroid function in normal women.
Due to their increased serum concentrations, it has been technically easier to develop assays for total thyroid hormones and these are more accurate and valid than free hormone assays. 7 However, the rise in TBG causes total T4 to increase to 1.5 times the concentration typical in the non-pregnant individual.What tests are appropriate? Growing points are the following: physiology of thyroxine delivery to the foetus. Establishment of gestational thyroid hormone reference ranges. Evaluation of strategies to screen thyroid function in early pregnancy.
The T4 Uptake is a similar test 11 FT4 The free T4 (FT4) test measures the concentration of free thyroxine, the only biologically active fraction, in the serum. The free thyroxine is not affected by changes in concentrations of binding proteins.9 Therefore, it is essential to rely on T4 and T3 (either bound or free) to assess thyroid status in early gestation, although TSH will be significantly elevated in overt hypothyroidism.
This review will focus on thyroid function in pregnancy followed by a discussion of thyroid dysfunction and its effects. Thyroid physiology and function in normal pregnancy. Pregnancy has an appreciable effect on thyroid economy.TSH Suppression of TSH with an elevation of free T4 is a common finding during the first trimester of pregnancy 1,11,12. These findings are believed to be caused by stimulation of the TSH receptor by hCG which results in an increase in FT4 and subsequently suppresses TSH levels 11.
For this reason, there is significant method-dependant variation in FT4 measurement in pregnancy. Therefore, it is necessary to use method- and gestation-specific reference intervals for the interpretation of various laboratory results during pregnancy.3 A recommended daily iodine intake of 250 g/day (suggested by a WHO consultation) represents an increase from the previous figure of 200 g/day. In the pregnant woman, a median urinary iodine (UI) of 150 g/l is regarded as insufficient, an excretion of 150249 as adequate, that of 250499 as more than adequate and 500.
Measurement of thyroid-stimulating antibodies and antithyroid peroxidase antibodies is useful for diagnosis of thyroid disease in pregnancy. Treatment of Graves hyperthyroidism should be done with propylthiouracil for first trimester only, then carbimazole or methimazole.What is Total Thyroxine? The total thyroxine test is typically ordered to measure thyroid function. Patients with symptoms of hyperactive or hypoactive thyroid may present with abnormal total thyroxine levels. Goiter and infertility testing may also include total thyroxine blood tests.
Thus conditions associated with an increase in serum proteins such as pregnancy will cause a low resin uptake, because more labeled T3 binds to proteins and less labeled T3 is available to bind to the resin.TPO antibodies are a marker for an increased risk of infertility, miscarriage and preterm delivery. 10 TPOA bs are found in around 10 of women in early pregnancy and are also associated with decreased thyroid functional reserve during gestation with possible development of hypothyroidism.
Data from 606 normal pregnancies showing the rise in TBG (top panel) accompanied by the changes in FT4 and FT3 concentrations throughout gestation in a mildly iodine deficient area (Brussels). The lower 2 panels show the relationship between serum TSH and hCG as a function of gestational age and the relation between FT4 and hCG.Changes in Thyroid Function Test (TFT) Results Due to Pregnancy N ormal changes in thyroid function tests during pregnancy include a transient suppression of thyroid-stimulating hormone and stimulation of triiodothyronine.1,2. Serum total T4 and total T3 steadily increase during pregnancy to approximately 1.5 times the non-pregnant level by mid second trimester 3-6.
Adapted from Glinoer, DG (1997)1 with permission. It is probable that the changes in thyroid hormone during gestation relate to the necessity of delivering thyroxine to the foetal cells, particularly neuronal cells.Circulating T4 and T3 are at equilibrium with free- and protein-bound hormones. The majority of thyroid hormones ( 99) are bound to transport proteins, mainly to TBG and to a lesser extent to transthyretin and albumin.
The resin T3 uptake value is not reduced as it should be in pregnancy, and confirms that the suppressed TSH and elevated thyroxine level are not due pregnancy. Patterns of Thyroid Function Tests TSH FT4 FT3 Possible Etiologies Low Low Central hypothyroidism Euthyroid sick syndrome Normal Normal Subclinical hyperthyroidism Normal High T3 -toxicosis.E-mail:.uk Accepted. November 29, 2010. Abstract Advances in understanding the physiology of thyroid function in normal pregnancy have highlighted the importance of the consequences of abnormal function on obstetric outcome and foetal well-being.
Adequate concentrations of T4 are essential for neural development and this T4 can only be maternally derived from, at least during the first trimester. The placenta plays an important role in T4 transport, although details are still unclear.John H. Lazarus Centre for Endocrine and Diabetes Sciences, Cardiff University School of Medicine, University Hospital of Wales, Heath Park, Cardiff CF14 4XN, UK Correspondence address. Centre for Endocrine and Diabetes Sciences, Cardiff University School of Medicine, University Hospital of Wales, Heath Park, Cardiff CF14 4XN, UK.
J Clin Endocrinol Metab 2000;. 7. Amerlex free triiodothyronine and free thyroxine levels in normal pregnancy. Br J Obstet Gynaecol. 1985;. 8. McElduff A Measurement of free thyroxine (T4) levels in pregnancy.However, in most clinical laboratories total T4 testing has been replaced with free hormone assays. In general, commercial FT4 immunoassays are affected to variable degrees by the physiological increase in the TBG that occur in pregnancy.
Panesar Ns, et al. Reference intervals for thyroid hormones in pregnant Chinese women. Ann Clin Biochem. 2001;. MEDLINE 16. Castracane VD and Gimpel T. Reference Values in Pregnancy for IMMULITE Assays.A longitudinal study of serum TSH and total and free iodothyronines during normal pregnancy. Acta Endocrinol 1982;. 5. Pedersen KM, et al. Amelioration of some pregnancy associated variation in thyroid function by iodine supplementation.
Does the patient have symptoms or signs consistent with the laboratory diagnosis? Consider common etiologies first Example Thyroid Profiles Normal Profile Test Result Units Reference Range T4 Total 15.8 ug/dl 4.5 - 12.0 T3 Uptake 18.5 24.3 - 39.0 FT4 Index 2.9 ug/dl 1.2 - 4.9 TSH 0.923 uIU/ml 0.34 - 5.6 The TSH, and.Areas timely for developing research are the following: placental thyroid hormone physiology, thyroid hormone therapy and screening thyroid function. Introduction During the last 20 years, it has been appreciated that thyroid physiology changes significantly during gestation.