It also contains calcitonin (a hormone produced in the thyroid gland involved in the regulation of calcium levels), T1 and T2; these are not present in synthetic hormone medication. This extract was once a mainstream hypothyroidism treatment, but its use today is unsupported by evidence; British Thyroid Association and American professional guidelines discourage its use, as does NICE. Subclinical hypothyroidism
There is no evidence of a benefit from treating subclinical hypothyroidism in those who are not pregnant, and there are potential risks of overtreatment. Untreated subclinical hypothyroidism may be associated with a modest increase in the risk of coronary artery disease when the TSH is over 10 mIU/L. A 2007 review found no benefit of thyroid hormone replacement except for "some parameters of lipid profiles and left ventricular function". There is no association between subclinical hypothyroidism and an increased risk of bone fractures, nor is there a link with cognitive decline.Since 2008, consensus American opinion has been that in general people with TSH under 10 to 20 mIU/L do not require treatment.American guidelines recommend that treatment should be considered in people with symptoms of hypothyroidism, detectable antibodies against thyroid peroxidase, a history of heart disease or are at an increased risk for heart disease, if the TSH is elevated but below 10 mIU/L. NICE recommends that those with a TSH above 10 mIU/L should be treated in the same way as overt hypothyroidism.
Hypothyroidism in early pregnancy, even with limited or no symptoms, may increase the risk of pre-eclampsia, offspring with lower intelligence, and the risk of infant death around the time of birth. Women are affected by hypothyroidism in 0.3–0.5% of pregnancies. Subclinical hypothyroidism during pregnancy is associated with gestational diabetes, low birth-weight, placental abruption, and the birth of the baby before 37 weeks of pregnancy. Children
Newborn children with hypothyroidism may have normal birth weight and height (although the head may be larger than expected and the posterior fontanelle may be open). Some may have drowsiness, decreased muscle tone, a hoarse-sounding cry, feeding difficulties, constipation, an enlarged tongue, umbilical hernia, dry skin, a decreased body temperature, and jaundice. A goiter is rare, although it may develop later in children who have a thyroid gland that does not produce functioning thyroid hormone. A goiter may also develop in children growing up in areas with iodine deficiency. Normal growth and development may be delayed, and not treating infants may lead to an intellectual impairment (IQ 6–15 points lower in severe cases). Other problems include the following: difficulty with large scale and fine motor skills and coordination, reduced muscle tone, squinting, decreased attention span, and delayed speaking. Tooth eruption may be delayed.In older children and adolescents, the symptoms of hypothyroidism may include fatigue, cold intolerance, sleepiness, muscle weakness, constipation, a delay in growth, overweight for height, pallor, coarse and thick skin, increased body hair, irregular menstrual cycles in girls, and delayed puberty.