Hypothyroidism is what is usually called hypothyroidism, which is a disease caused by a decrease in the level and role of thyroid hormones (T3 and T4), often manifested as fear of cold, swelling, bloating, constipation and weakness, and thyroid function tests show elevated serum thyrotropin (TSH) and low T3 and T4 levels. What is the effect of subclinical hypothyroidism on pregnancy? Some studies have shown that subclinical hypothyroidism can also have an adverse effect on the fetus. Hypothyroidism can lead to increased miscarriage and neonatal mortality, and surviving offspring are prone to mental retardation even if they have normal nail function. Overseas people observed more than 25,000 pregnant women’s serum specimens, and found that 62 children with subclinical hypothyroidism were born normal, but 7-9 years later, their intelligence, attention, language expression, reading ability, school performance and vision were lower than normal in 15 indicators, and all IQ scores were 7 points lower than those of the control group, 19% of which had IQ scores below 85. All IQ scores were 7 points lower than the control group, with 19% of the IQ scores below 85, compared to 5% in the control group. Since subclinical hypothyroidism during pregnancy can cause a decrease in the child’s intelligence, it is advisable for women who are planning to become pregnant to undergo TSH screening for early detection of hypothyroidism and to treat it before pregnancy. Once subclinical hypothyroidism is detected, thyroid hormone replacement therapy should be given before pregnancy so that the effects on the child’s intelligence can be avoided, although medication should be continued during pregnancy and changes in thyroid function should be monitored. People with goiter, elevated autoantibodies to the thyroid, other autoimmune endocrine disorders or symptoms suggestive of hypothyroidism, or people with thyroid disease in their family should have TSH testing before planning a pregnancy, as there is evidence that these people are more likely to develop hypothyroidism than the general population. There are many causes of hypothyroidism, but the most common one is autoimmune thyroiditis. Because of genetic susceptibility, people with a family history of the disease are prone to it, and these people should be vigilant and try to avoid triggers that aggravate the onset of the disease, such as a low-iodine diet, avoiding excessive stress and mental stimulation, and refraining from smoking, all of which are measures that are beneficial in preventing the onset of the disease.