Hypothyroidism in pregnancy,:
Hypothyroid women often present with anovulatory menstruation, infertility, and, less commonly, combined pregnancy. The most common form of hypothyroidism in pregnancy is autoimmune thyroid disease – chronic lymphocytic thyroiditis. It is caused by a diffuse lymphocytic infiltration in the thyroid tissue due to antibodies produced by the body’s immune dysfunction, resulting in an enlarged thyroid gland and hypothyroidism. Normal maternal thyroid function is very important for both the mother and the developing fetus, especially in early pregnancy, when the mother is the sole source of thyroid hormones for the fetus. Disorders of thyroid function can have serious adverse consequences for the mother and the fetus. Therefore, laboratory evaluation of maternal thyroid function during pregnancy is essential for the accurate diagnosis and timely treatment of thyroid disorders.
Causes of hypothyroidism in pregnancy
1. Thyroid hypothyroidism.
2, hypothyroidism secondary to hypothalamic or pituitary lesions.
3, thyroid hormone resistance syndrome.
4.Gestational combined hypothyroidism
(1) Hypothyroidism originated in early childhood or adolescence, and pregnancy after treatment.
(2) Hypothyroidism originated in adulthood, and pregnancy after treatment.
(3) Hypothyroidism secondary to hyperthyroidism or adenoma after radiotherapy or surgery, and pregnancy after treatment. About 1% of women with hypothyroidism can become pregnant after treatment.
The risks of hypothyroidism in pregnancy
Clinical hypothyroidism during pregnancy in fertile women can lead to reduced fertility, gestational hypertension, placental abruption, spontaneous abortion, fetal distress, preterm birth and low birth weight babies. In early pregnancy, the fetus is completely dependent on the mother for thyroid hormones. The fetus requires T4 for normal brain and neurological development as well as for the development of other organ systems. Fetal thyroid function is not fully established until mid-gestation. A decrease in maternal thyroid hormone may result in incomplete differentiation and development of the parts of the cerebral cortex responsible for speech, hearing and intelligence during fetal development.
There are conflicting conclusions as to whether the risk of pregnancy complications is increased in subclinical hypothyroidism.
Symptoms of hypothyroidism in pregnancy
The most common symptoms of hypothyroidism in pregnancy include fatigue, weakness, weakness, drowsiness, apathy, depression, and slow response. Hair loss, dry skin, low sweating, and weight gain despite poor appetite may also occur. There may be painful muscle tonicity, pain and burning sensation in the fingers and hands, or abnormal tingling-like sensation, slow and weak heartbeat, reduced heart sounds, a few palpitations, shortness of breath, low or hoarse voice, and prolonged delayed deep tendon reflexes. The physical signs are slowness of movement and speech, pale, dry, inelastic skin, sunken edema in the late stage, thin and dry hair, and no luster. The thyroid gland is diffusely or nodularly enlarged.
Subclinical hypothyroidism has no obvious clinical symptoms. Laboratory tests show elevated serum TSH and normal FT4 and TT4. Isolated hypo-T4emia is defined as a normal TSH during pregnancy with only a decrease in T4 or FT4. The consensus view on TSH is that the TSH reference range should be lower in early pregnancy than in the non-pregnant population, and TSH 2.5 mIU/L is currently recommended as a conservative upper limit in early pregnancy.
Screening for hypothyroidism in pregnancy
1.Serum TSH test
It is the best indicator to diagnose hypothyroidism. An increase in TSH level combined with serum free thyroxine index (FT4I) and thyroid peroxidase antibodies or other antibodies detection; FT4I is lower than normal, suggesting a deficiency of biologically active thyroid hormones in the body.
2.Serum T4 test
The abnormal results such as lower than normal serum T4 value and significantly lower resin T3 uptake ratio (RT3U) are often obtained before the appearance of clinical symptoms.
3. Routine blood tests
Patients with hypothyroidism often have anemia (30%-40%). Because of the decrease of red blood cell production rate, most of them are orthocytic anemia; there are also megaloblastic anemia due to vitamin B12 or folic acid deficiency; if small cell anemia is present, it is mostly due to the presence of iron deficiency at the same time. The white blood cell and platelet counts are basically normal, but occasionally bleeding may occur due to abnormal platelet function.
4.Other biochemical tests
Elevated lipid, creatinine and phosphokinase concentrations are often found. Liver function tests may have mild reversible abnormalities.
Diagnosis of hypothyroidism in pregnancy
Mild hypothyroidism is difficult to diagnose during pregnancy because the symptoms are not obvious and non-characteristic. However, if symptoms are obvious (fatigue, coldness, edema, dry hair, rough skin, etc.), the diagnosis is not difficult when combined with history, physical signs and laboratory tests. Women treated with antithyroid drugs for hyperthyroidism during pregnancy should also be tested for goiter in the fetus. Amniotic fluid levels of iodothyronine and TSH reflecting fetal plasma levels are useful in the diagnosis of prenatal hypothyroidism. Cord blood specimens are more accurate in making a diagnosis.
Treatment of hypothyroidism in pregnancy
Women diagnosed with hypothyroidism before pregnancy who are on levothyroxine therapy should have their levothyroxine dose adjusted before pregnancy to keep TSH below 2.5 mIU/L.
1. Thyroxine tablets, adjust the dosage according to thyroid function.
2. Levothyroxine tablets (levothyroxine) (L-T4), a synthetic hormone with easily standardized doses, is superior to thyroxine tablets and thus has the potential to replace them. The drug is best taken in the early morning on an empty stomach. During early pregnancy, it is often not easily tolerated on an empty stomach, so it can be postponed until there is no nausea and vomiting. Ferrous sulfate and T4 taken together can form insoluble iron thyroxine complexes, reducing the absorption of thyroxine, so the two must be taken separately at intervals of more than 2 small handsets.
3, in the T4 replacement therapy at the same time, should strengthen nutrition, pay attention to rest, do not overwork.
4. Do regular prenatal checkups, pay attention to the growth of weight, abdominal circumference and uterine height, and use ultrasound to monitor fetal growth and development, so as to detect intrauterine growth retardation in time and give appropriate treatment as early as possible. During delivery, the mother was given oxygen inhalation, encouraged to eat, infused with fluids if necessary, and monitored the fetal heart during labor. During the second stage of labor, most women with congenital hypothyroidism have insufficient strength of the rectus abdominis muscle, and are often unable to hold their breath and push downward, and cannot increase abdominal pressure well. Make good preparation for neonatal resuscitation. The mother with Hashimoto’s disease should keep the umbilical cord blood to check the anti-thyroid antibodies. After the third stage of labor, pay attention to postpartum bleeding and give uterine contraction agents.
5, the treatment of neonatal hypothyroidism, the incidence of neonatal hypothyroidism is 1 / 4000, the problem is congenital hypothyroidism, no clinical manifestations at birth, often in later growth and development gradually appear symptoms of hypothyroidism, more serious is the emergence of mental retardation, many regions of the world have carried out research on the prevention of neonatal hypothyroidism, and began to screen newborns for hypothyroidism. Infants with congenital hypothyroidism have low T4 levels and high TSH levels, and blood tests are easy to diagnose and monitor.
6. During pregnancy, if thyroid function is stable under levothyroxine treatment, it is recommended that TSH be measured every 6 to 8 weeks. if the levothyroxine dose is adjusted, it should be measured every 4 to 6 weeks. Mothers who have not been adequately treated in early pregnancy need to have their TSH measured every 2 weeks.
Treatment of subclinical hypothyroidism during pregnancy
(i) Subclinical hypothyroidism: increased serum TSH and normal FT4;
②Low T4emia: normal serum TSH and reduced FT4;
③TPOAb positive. The three conditions, which can exist alone or overlap, can be present.
The effect of untreated subclinical hypothyroidism on the intellectual development of offspring has been reported. A recent evidence-based study recommended levothyroxine treatment for pregnant women with subclinical hypothyroidism. The dose of levothyroxine given to pregnant women with subclinical hypothyroidism should be lower than 2.5 mlU/L of TSH as soon as possible, and thyroid function should be monitored every 4-6 weeks during treatment to adjust the dosage of the drug in a timely manner.
Prognosis of the newborn
Numerous studies have shown that untreated hypothyroidism is associated with stillbirth, preterm birth, congenital anomalies and reduced intelligence quotient (IQ). Neonatal mortality and reduced IQ do not differ from normal neonates when treated with levothyroxine replacement therapy and targets are met.