The functioning of the thyroid gland is considerably altered by pregnancy. The production of thyroxine (T4) and triiodothyronine (T3) increases by almost one and a half times during pregnancy. In healthy women, these changes occur seamlessly as part of the normal physiology of pregnancy, but many women with borderline thyroid status develop abnormalities in thyroid gland function during pregnancy. Thyroid dysfunction during pregnancy is widespread. This is why thyroid function is commonly assessed during pregnancy. Clinical features The symptoms of hypothyroidism during pregnancy and outside pregnancy are similar. Manifestations can range from fatigue, hair loss, dry skin, cold intolerance, weight gain and constipation. Many of these symptoms occur frequently during pregnancy, and identifying hypothyroidism based on symptoms can be misleading. Pregnant women with hypothyroidism often have no symptoms. Subclinical hypothyroidism (SCH) is usually asymptomatic and detected only by laboratory tests. Laboratory Findings To meet metabolic demands during pregnancy, thyroid physiology is altered and is manifested by changes in thyroid function tests. Changes include elevated T4-binding globulin (TBG), which increases total T4 and T3 levels 1.5 times higher than in a non-pregnant state. Furthermore, elevated serum human chorionic gonadotropin (hCG) levels, particularly in early pregnancy, lead to reduced serum thyroid-stimulating hormone (TSH) levels during the first trimester. If the population- and trimester-specific reference range for TSH is not available, an upper reference threshold of approximately 4 mU/L can be used. Trimester-specific reference values ​​for free T4 (FT4) should be provided with the test kits. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get an original essay High levels of bound T4 during pregnancy can make assessment of FT4 difficult. Tests based on separation methods such as equilibrium dialysis or ultrafiltration are laborious, time-consuming, expensive and poorly available. Measurement of FT4 is performed by indirect analog immunoassays by the majority of clinical laboratories, largely due to its ability to be performed rapidly on automated platforms. Total T4 measurement may be superior to FT4 immunoassay measurement in pregnant women. However, reference ranges must take into account the 50% increase in TBG occurring during pregnancy. Anti-thyroid peroxidase (TPO) antibodies are elevated in 30-60% of pregnant women with elevated TSH. The risk of complications is higher in women with positive SCH and TPO antibodies than in those with negative TPO antibodies. If serum TSH is >2.5 mU/L, an estimate of TPO antibodies should be performed. TPO antibody positivity may swing the decision to initiate T4 therapy in pregnant women with a TSH between 2.5 and 4.0 mU/L and may also help predict the risk of postpartum thyroid dysfunction. Diagnosis Diagnosis of primary hypothyroidism in pregnancy is based on the finding of an elevated serum TSH level, calculated using population- and trimester-specific TSH ranges for pregnant women. Any woman with suggestive symptomshypothyroidism should have a TSH assessment. There is insufficient evidence to recommend or against routine screening for thyroid dysfunction in asymptomatic pregnant women, but TSH estimation is usually performed during the first trimester of pregnancy in clinical practice. As recommended by the 2017 American Thyroid Association (ATA) Guidelines, the following trimester-specific ranges and thresholds may be considered when local assessments are not available. During the first trimester, the lower reference range of TSH can be decreased by 0.4 mg/L, while the upper reference range is reduced by 0.5 mU/L. This generally corresponds to an upper reference limit of TSH of 4.0 mU/L. Women with central hypothyroidism due to pituitary or hypothalamic disease will not have elevated TSH concentrations during pregnancy. For women in the first trimester of pregnancy with a TSH greater than 4.0 mU/L, the FT4 or total T4 value should be estimated to differentiate SCH from overt hypothyroidism. Pregnancy Complications Hypothyroidism may have adverse effects on pregnancy outcome, depending on the severity of the pregnancy. biochemical abnormalities: Overt hypothyroidism Subclinical hypothyroidism Maternal hypothyroxinemia (low isolated maternal FT4) Overt hypothyroidism — Overt uncorrected hypothyroidism during pregnancy is unusual (0.3 to 0.5% of women screened). Anovulation in hypothyroid women and increased rates of first trimester spontaneous abortions (often undetected) are responsible for this finding. In continuing pregnancies, hypothyroidism has been associated with an increased risk of several complications, including: Preeclampsia and gestational hypertension Placental abruption Non-reassuring fetal heart rate monitoring Premature delivery, including very preterm delivery (before 32 weeks) Low birth weight Increased rate of cesarean sections Postpartum hemorrhage Perinatal morbidity and mortality Neuropsychological and cognitive impairment in children Subclinical hypothyroidism - SCH is more common than overt hypothyroidism. In areas where iodine is sufficient, 2.0 to 2.5% of women screened have SCH. Women with SCH are less likely to develop complications than those with overt disease. In some, but not all, studies, women with SCH were at increased risk of severe preeclampsia, preterm delivery, placental abruption, and/or miscarriage compared to euthyroid women. It is unclear whether children of women with SCH are at risk for neuropsychological impairment. Observational studies suggest a possible association between SCH during pregnancy and impaired cognitive development in children. Women with SCH and positive TPO antibodies tend to have a higher risk of adverse pregnancy outcomes. The risk of complications increases in TPO-positive women with TSH > 2.5 mU/L, but is not consistently demonstrated in TPO-negative women until TSH values ​​exceed 5 to 10 mU/L. Pregnancy outcomes in women undergoing in vitro fertilization may be worse in those with preconception TSH values ​​above 2.5 mU/L. Low Maternal Free T4 — Isolated maternal hypothyroxinemia is defined as a maternal FT4 level in the lower 2.5 to 5 percentiles of the reference range as well as a TSH concentration in the normal range. It has not been clearly demonstrated that isolated maternal hypothyroxinemia is associated with worsening of..