Thyroxine is very important for fetal development, especially for neurological development of the fetus. It is especially important during early pregnancy. Hypothyroidism can cause embryonic abortion, known as recurrent miscarriage, in about 60% of pregnancies. Even in those who are lucky enough not to have a miscarriage, there is a risk of preterm birth, low birth weight, gestational hypertension, fetal death, and mental retardation, which must be taken seriously!
Physiological changes of thyroid hormone during pregnancy
During pregnancy, thyroxine and related factors in the body undergo a series of changes, with total T4 (TT4) being 1.5 times higher than normal, TSH dropping to a minimum between 8 and 10 weeks of pregnancy and returning to normal at 12 weeks of pregnancy, and FT4 generally remaining unchanged. Due to the physiological changes in thyroid function during pregnancy.
Therefore, using normal human standards to measure thyroid function during pregnancy can easily lead to underdiagnosis of hypothyroidism .
Reference values of thyroid hormones during pregnancy
In October 2011, the American Thyroid Association issued new guidelines for the management of thyroid disorders in pregnancy and the postpartum period, which include the following recommendations.
1. The main indicators of thyroid disorders during pregnancy are TSH and T4.
2. The standard values usually used are: 0.1-2.5 mIU/L in early pregnancy, 0.2-3.0 mIU/L in mid-pregnancy, and 0.3-3.0 mIU/L in late pregnancy.
If each laboratory has its own pregnancy-specific standard values, they should be considered first.
Hypothyroidism-related diseases during pregnancy and diagnostic criteria
The disorders associated with hypothyroidism during pregnancy are
1. clinical hypothyroidism. (hypothyroidism)
2, Subclinical hypothyroidism (SCH).
3. normal thyroid function but positive thyroid antibodies: positive thyroid peroxidase enzyme antibodies (TPO-Ab) positive thyroglobulin antibodies (TG-Ab.)
4. Hypo-T4emia .
Diagnosis of various diseases.
1. Diagnosis of clinical hypothyroidism: TSH>2.5 mIU/L, and decreased T4 level. Or TSH>10.0 mIU/, with or without T4 decrease.
2.Diagnosis of subclinical hypothyroidism: TSH between 2.5-10 mIU/L, without T4 decrease.
3. Hypotensive T4emia: TSH is normal, but T4 level is below the 5th or 10th percentile of the reference range.
Management of hypothyroidism-related diseases during pregnancy
1.Clinical hypothyroidism drug treatment.
①L-T4 (levothyroxine) is recommended, T3 or dry thyroid tablets are not recommended.
②Patients with hypothyroidism who are on L-T4 therapy should have their TSH adjusted to less than 2.5 mIU/L before pregnancy and increase L-T4 by 25-30% immediately after pregnancy. This is done by increasing the dose from once a day to 9 times a week.
③The frequency of TSH check after pregnancy in hypothyroid patients is at least once a month and at least once during 26-32 weeks of pregnancy.
④In addition to regular testing of maternal thyroid function after pregnancy in hypothyroid patients, there is no need to add other additional tests if there is no other pregnancy pathology.
2 .Treatment of subclinical hypothyroidism.
Subclinical hypothyroidism during pregnancy should be treated with L-T4 intervention. The goals of treatment, medication and testing methods are the same as those for clinical hypothyroidism. It is important to pay attention to the possibility of subclinical hypothyroidism to develop into clinical hypothyroidism. TSH and T4 values should be tested every 4 weeks at 16 weeks of pregnancy and at least once at 26 weeks of pregnancy and 32 weeks of pregnancy.
3. Treatment of simple hypo-T4emia.
There is no conclusive evidence on the adverse effects of pure hypo-T4 on pregnancy, and no clinical trials have demonstrated the benefit of L-T4 therapy, so the Guidelines do not recommend treatment for this group of patients.
4. Treatment of positive thyroid antibodies.
Positive thyroid antibodies are associated with miscarriage, preterm birth, perinatal death, and offspring development of mental and motor skills. Treatment with selenium may be beneficial for those with positive thyroid antibodies prior to pregnancy. One study suggests that 200ug of selenium per day before pregnancy may not only result in a lower rate of postpartum thyroid abnormalities, but may also reduce thyroid antibody levels during pregnancy. The use of selenium during pregnancy has not been well evaluated and is not currently recommended for pregnant women with positive thyroid antibodies.
Antibody-positive pregnant women are prone to clinical or subclinical hypothyroidism during pregnancy. Therefore, thyroid function should be tested at least once a month during the first 5 months of pregnancy. Thyroid function is checked at least once during the second half of the pregnancy cycle between 26-32 weeks. When hypothyroidism or subclinical hypothyroidism occurs during pregnancy in this group of patients, the treatment is the same as above.