The functioning of the thyroid gland is significantly altered by pregnancy. The production of thyroxine (T4) and triiodothyronine (T3) increases 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 the functioning of the thyroid gland during pregnancy. Thyroid dysfunction during pregnancy is widespread. This is why thyroid function is commonly assessed during pregnancy. Clinical features Symptoms of hypothyroidism during pregnancy and in the non-pregnant state are similar. Manifestations can range from tiredness, hair loss, dry skin, cold intolerance, weight gain and constipation. Many of these symptoms commonly occur in pregnancy, and identifying hypothyroidism based on symptoms can be misleading. Pregnant women with hypothyroidism often do not experience any symptoms. Subclinical hypothyroidism (SCH) is usually asymptomatic and is detected only by laboratory tests. Laboratory Results To meet metabolic demands during pregnancy, the physiology of the thyroid is modified, which is manifested in changes in thyroid function tests. Changes include elevated levels of T4-binding globulin (TBG), which increase total T4 and T3 levels 1.5 times higher than in the non-pregnant state. Furthermore, elevated serum levels of human chorionic gonadotropin (hCG), particularly in early pregnancy, result in decreased serum thyroid-stimulating hormone (TSH) levels in the first trimester. If the population- and trimester-specific reference range for TSH is not available, a higher reference cut-off of approximately 4 mU/L can be used. Quarterly 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 Shouldn't Be Banned"? Get an original essay Elevated levels of bound T4 in pregnancy can make FT4 assessment difficult. Tests based on separation methods such as equilibrium dialysis or ultrafiltration are laborious, time-consuming, expensive, and not widely available. Measurement of FT4 is performed using indirect analog immunoassays by most clinical laboratories, largely due to its ability to be performed rapidly on automated platforms. Total T4 measurement may be superior to immunological FT4 measurement in pregnant women. However, reference intervals should take into account the 50% increase in TBG that occurs in pregnancy. Thyroid peroxidase (TPO) antibodies are elevated in 30-60% of pregnant women with elevated TSH. The risk of complications is greater in women with SCH and positive TPO antibodies than in those with negative TPO antibodies. If serum TSH is >2.5 mU/L, TPO antibody estimation should be performed. TPO antibody positivity may influence the decision to initiate T4 treatment in pregnant women with TSH between 2.5 and 4.0 mU/L and may also help predict the risk of postpartum thyroid dysfunction. Diagnosis The diagnosis of primary hypothyroidism during pregnancy is based on the finding of an elevated serum TSH level, calculated using population- and trimester-specific TSH ranges for pregnant women. All women with symptoms suggestive of hypothyroidism should have their TSH measured. There is insufficient evidence to recommend or against screeningroutinely for thyroid dysfunction in asymptomatic pregnant women, but in clinical practice TSH estimation is commonly performed in the first trimester of pregnancy. According to the recommendation of the 2017 American Thyroid Association (ATA) guidelines, the following trimester-specific ranges and cutoffs may be considered when local assessments are not available. In the first trimester, the lower TSH reference range can be reduced by 0.4 mg/l, while the upper reference range can be reduced by 0.5 mU/l. This usually corresponds to an upper TSH reference limit 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, FT4 or total T4 should be estimated to differentiate between SCH and overt hypothyroidism. Pregnancy Complications Hypothyroidism can have adverse effects on pregnancy outcomes, depending on the severity of the problem. biochemical abnormalities: Overt hypothyroidism Subclinical hypothyroidism Maternal hypothyroxinemia (isolated low maternal FT4) Overt hypothyroidism: Uncorrected overt hypothyroidism in pregnancy is unusual (0.3-0.5% of women screened). Anovulation in hypothyroid women and increased rate of miscarriage in the first trimester (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 tracking Preterm birth, including very preterm birth (before 32 weeks) Low birth weight Increased frequency of cesarean sections Postpartum hemorrhage Perinatal morbidity and mortality Neuropsychological and cognitive impairment in the infant Subclinical hypothyroidism: SCH is more common than overt hypothyroidism. In iodine-deficient areas, 2.0 to 2.5% of women screened have SCH. Women with SCH are less likely to develop complications than those with established disease. In some, but not all studies, women with SCH were reported to be at greater risk of severe preeclampsia, preterm birth, placental abruption, and/or miscarriage compared to euthyroid women. It is unclear whether children of women with SCH are at risk for neuropsychological deterioration. Observational studies suggest a possible association between SCH in pregnancy and impaired cognitive development in children. Women with SCH and positive TPO antibodies have a tendency for a higher risk of adverse pregnancy outcomes. The risk of complications increases in TPO-positive women with TSH > 2.5 mU/L, but was not consistently demonstrated in TPO-negative women until TSH values ​​exceeded 5-10 mU/L. Pregnancy outcome for women undergoing IVF may be worse among those with preconception TSH values ​​greater than 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 percentile of the reference range along with a TSH concentration in the normal range. Isolated maternal hypothyroxinemia has not been clearly demonstrated to be associated with worsening perinatal and neonatal outcome. In a multicenter study conducted in women with isolated maternal hypothyroxinemia, T4 supplementation showed no significant differences in neurodevelopmental or behavioral outcomes in children five years of age. Furthermore, no significant differences were found in the frequency of.