Thyroid disease -a highly vascular organ -a buferfly shape - situated at the front of the neck. - main function is to produce the iodine-rich hormones tri- iodothyronine (T3) and thyroxine (T4). - These hormones are secreted directly into the blood circulation in response to a negative feedback to the hypothalamus which secretes thyrotropin releasing hormone (TRH) that stimulate the anterior pituitary gland to secrete thyroid stimulating hormone (TSH)

- iodine, combines with an amino acid called tyrosine which enables synthesis of the thyroid hormones within the thyroid follicles Once in the blood circulation, 99% of T3 and T4 are bound to thyroxine-binding globulin (TBG) with the remaining 1% unbound or free: e.g. fT3 and fT4 -It is fT3, fT4 and TSH that are measured in thyroid function tests.

Excess T4 is converted to the more potent T3 by deionization in the peripheral tissue -Most body tissue has receptors for fT3, and once bound to the tissue, metabolic activities result. -The thyroid hormones regulate the metabolic rate throughout all body tissue and influence growth and maturity. -In pregnancy, the circulating level of TBG enables increased levels of T3 and T4, so only fT3 and fT4 should be measured by laboratory testing ,The fetus cannot synthesize T3 and T4 until the 10th week of pregnancy and is dependent upon maternal thyroid hormones from placental transfer Normal development of the fetal brain is dependent upon maternally derived T4 which is converted intracellularly to T3

-Thyroid disease is the second most common cause of endocrine dysfunction in pregnancy - is difficult to recognize as the symptoms mimic pregnancy . -The most common thyroid disorders in pregnancy are hypothyroidism and hyperthyroidism (thyrotoxocosis), being of considerable significance due to their effect on both the woman and fetus الجدول مهم .

Hypothyroidism -under-activity of the thyroid gland - with absent or low levels of thyroid hormones T3 and T4 - due to : @ malfunctioning thyroid tissue @ secondary to pituitary or hypothalamic disease. -The most common cause in pregnancy is: @ autoimmune thyroiditis @ goitre may or may not be present Lack of dietary iodine can also cause goitre

Definition of Goitre: is enlarged thyroid tissue due to infiltration of lymphocytes and increase of fibrous tissue; this condition is also known as Hashimoto's disease. -Hypothyroidism : -is familial - may be associated with other autoimmune disease such as type 1 diabetes Symptoms include : -weight gain - intolerance to cold temperature - constipation

- alopecia-dry skin - lethargy - hoarse voice -ataxia - bradycardia - cognitive impairment. - Menstrual irregularities and infertility are common, because TRH stimulation induces hyperprolactinaemia which prevents ovulation.

-Not all women have symptoms and consequently the disease might be first recognized during infertility investigations. - The most serious complication of untreated hypothyroidism is myxoedema coma which presents with hypothermia, hypoventilation and bradycardia, followed by unconsciousness

Pregnancy complications of hypothyroidism are: hypertension low birth weight psychomotor retardation in the fetus. raise concern of the low Intelligence Quotient (IQ) of children born to mothers with untreated hypothyroidism cretinism may result from severe maternal iodine deficiency associated with hypothyroidism.