HYPOTHYROIDISM AND PREGNANCY
Thyroid hormones are necessary for fertility, conception and normal progression of pregnancy. If a woman with hypothyroidism wishes to become pregnant, the thyroid function should be within normal levels (optimal levels of Thyroid-Stimulating Hormone TSH are < 2.5 IU / ml) and if not, then it may be necessary pregnancy should be delayed until they are regulated.
Thyroid hormones of the pregnant woman must also meet the needs of the developing fetus, especially the first half of pregnancy. If pregnant women do not have adequate thyroid hormones, there is high risk of neurodevelopmental delay to the fetus. This means that women with hypothyroidism, should continue thyroxine tablets in pregnancy and they often need to increase their thyroxine dose by 30-50% within the first 6 weeks of pregnancy. If hypothyroidism is inadequately treated in pregnancy, may cause increased blood pressure, anaemia, weakness, muscle pains, premature birth or even miscarriage. The dose of thyroxine should be reduced to the pre-pregnancy levels immediately following childbirth.
Hypothyroidism in early pregnancy
Hypothyroidism is the most common thyroid condition that affects pregnancy in 2-3% women (1:50 subclinical, 1:500 severe clinical hypothyroidism). If it is not diagnosed and treated during pregnancy it may increase the risk of complications such as miscarriage, placental abruption, pre-eclampsia, anaemia, premature birth and postpartum haemorrhage.
The diagnosis is made if, in the first trimester of pregnancy, TSH is found >2.5 IU/ml in two different blood tests, especially in women who are at increased risk for developing thyroid disease. In these cases, thyroid autoantibodies should be checked and evaluated by an endocrinologist to initiate thyroxine treatment. Thyroid functions tests should be performed every 4 weeks during pregnancy until the 24th week and every 6 weeks later on. In women who have not experienced clinical hypothyroidism but only a slight increase in TSH during pregnancy, discontinuation of postpartum therapy and frequent monitoring are usually recommended.
THYROTOXICOSIS AND HYPERTHYROIDISM
Thyrotoxicosis is the condition characterised by the increased levels of thyroid hormones in the body. Pregnancy itself, due to the action of pregnancy hormones such as beta-chorionic gonadotropin, can lead to a relative increase in thyroid hormones in the blood, without the presence of any pathological condition. Hyperthyroidism means autonomous thyroid hyperfunction, i.e., occurs when the thyroid produces too much T3 and T4 hormones and this needs more investigation and possibly initiation of treatment. The overactive thyroid affects the way the body uses energy and can affect both fertility and the progression of pregnancy.
Pregnant women with uncontrolled hyperthyroidism may experience tachycardia, hypertension and heart problems and have an increased risk of miscarriage, premature birth and the birth of a baby with very low weight. Hence, it is really important that women with hyperthyroidism who become pregnant, they should contact their endocrinologist immediately to modify the treatment, especially during the first trimester. Close monitoring should be every 3-4 weeks so that drug therapy is formulated according to the needs of pregnancy.
What can cause thyrotoxicosis or hyperthyroidism during pregnancy?
- Graves ‘ disease. Graves ‘ disease, an autoimmune disease, is the most common cause of hyperthyroidism in women of reproductive age. In this case the autoantibodies produced activate the thyroid, and stimulate the production of more thyroid hormones than the body needs. Most women are usually diagnosed and commence treatment before pregnancy.
- Hyperemesis gravidarum. Women who have severe nausea and vomiting in the first trimester of pregnancy may also have thyroid dysfunction and, sometimes, may develop transient hyperthyroidism of pregnancy. This type of hyperthyroidism is due to the high levels of beta-chorionic gonadotropin (B hCG), one of the main hormones of pregnancy and usually subsides after the 14th-18th week of pregnancy (after the 4th month). It does not need drug therapy but close monitoring. If the TSH hormone remains too low (<0.1 IU/ml) and symptoms of hyperthyroidism coexist, then a real thyroid disease that needs treatment may coexist.
- Thyroid nodules. Sometimes hyperthyroidism in pregnancy can start from a thyroid gland that produces large amounts of hormones.
- Gestational hyperthyroidism is usually mild and transient so it rarely needs treatment.
What are the symptoms of hyperthyroidism?
Pregnant can complain about:
- Excessive heat
- Tachycardia
- Trembling of the hands
- Weight loss or difficulty gaining weight
- Fatigue
- Sleep disturbance
- Irritable mood, severe stress
How can hyperthyroidism be diagnosed in pregnancy?
During pregnancy usually the first suspicion comes with a very low value of TSH at the initial thyroid check. In this case, the blood test measurement should be repeated, as well as other thyroid hormones and should be evaluated by an endocrinologist.
If there are prominent symptoms of hyperthyroidism, treatment with antithyroid drugs and very frequent monitoring may be required. The diagnosis during pregnancy and breastfeeding is based on the clinical examination of the pregnant woman and the repeated thyroid functions tests, as scintigraphy is contraindicated.
Antithyroid drugs should be commenced in women with symptomatic clinical hyperthyroidism. The most preferable drug during the first trimester of pregnancy is propylthiuracil (PTU) and when it is administered frequent liver function tests should be performed every trimester. Methimazole, a common antithyroid drug, is not suitable for the first trimester of pregnancy as it rarely causes genetic disorders, however, it is the drug of choice for the second and third trimesters.
The target of antithydoid drug treatment is to maintain thyroid hormones at higher normal levels because there is a risk of fetal hypothyroidism if thyroid function is significantly suppressed. For this reason, the dosage of medicines may need to be changed both during pregnancy and after childbirth.
In pregnancy, treatment with radioactive iodine is prohibited, so the alternative treatment is the partial or total removal of thyroid gland to improve the disease. Surgery can be done safely during the second trimester (4th-6th month). Finally, antithyroid drugs could be continued in breastfeeding women without any side effects. Treatment with radioactive iodine could be performed when women stop breastfeeding.
Fetal monitoring in women with hyperthyroidism
Maternal hyperthyroidism has an increased risk of fetal complications, therefore fetal growth should be monitored by the obstetrician with growth scans at least every 4 weeks. Also, the fetal heart should be auscultated in every antenatal visit to ensure that fetal tachycardia is excluded.
Will baby need special care after childbirth?
Graves ‘ disease is an autoimmune condition and its autoantibodies can activate the thyroid. These antibodies can cross the placenta and cause hyperthyroidism to the baby. Pregnant women with present or past history of Graves ‘ disease should have thyroid autoantibodies checked during pregnancy, specifically after the 24th week, when the fetal thyroid begins to function. If they are elevated above the threshold, the baby may need special monitoring during pregnancy and for the first 2 weeks after childbirth and, sometimes, may need treatment. Neonatal Graves ‘disease is rare (1: 25000 births, ~ 2% of pregnancies with Graves’ disease) and is a self-limiting disease, lasting 1-3 months.
CHRONIC THYROTOIDITIS AND PREGNANCY
Up to 15% of young women have elevated antibodies against thyroid and chronic thyroiditis. Positive antithyroid antibodies are found in 17-30% of women with recurrent miscarriages in first trimester or infertility. A woman with Hashimoto thyroiditis who wishes to conceive should discuss with her doctor what should be the ideal levels of TSH hormone to favour conception and whether she will need to start treatment with thyroxine before pregnancy. If she becomes pregnant, TSH should be monitored every month because there is an increased risk of developing hypothyroidism during pregnancy; initiation of therapy is recommended if TSH is >2.5 IU / ml.
There is not enough evidence to recommend systematic screening for antithyroid antibodies in early pregnancy. Thyroid antibodies should be checked:
In an individual / family history of thyroid autoimmunity or other autoimmune diseases (especially Type 1 diabetes)
- History of infertility
- History of miscarriages
- Presence of goittre
- TSH >2.5 IU / ml
Women who have elevated antithyroid antibodies before pregnancy have an increased risk of developing postpartum thyroiditis, a relatively acute thyroid disorder that usually occurs 6-8 weeks following childbirth. This can cause changes in hormone levels and intense symptoms in the new mother, such as significant fatigue, depression, breastfeeding disorder etc.
Typically, postpartum thyroiditis has 3 phases: initial hyperthyroidism (6 weeks -3 months postpartum), followed by hypothyroidism (3 – 9 months after) and return to normal function (up to 1 year postpartum), although hypothyroidism may be permanent. The hyperthyroid phase does not require treatment. In contrast, hypothyroidism can be treated with administration of thyroxine tablets. Postpartum thyroiditis may recur in a future pregnancy and 30% of these women may develop permanent hypothyroidism in the future.
THYROID NODULES AND PREGNANCY
Thyroid nodules are small “lumps” within the thyroid gland and are benign (non-cancerous) in 95% of cases. A small percentage of nodules (~10%) can produce increased amounts of hormones and cause hyperthyroidism.
If a nodule is found incidentally during pregnancy during physical examination or if it exists before a thyroid ultrasound should be performed to assess its exact size and whether it is solid or cystic (filled with fluid). Depending on the results of ultrasound, diagnostic biopsy of the nodule should be performed or simply follow-up and re-examination after pregnancy. Usually, thyroid nodules do not affect thyroid function or pregnancy, so their treatment could be postponed until after childbirth. In the event that the biopsy of the nodule is suspicious, surgical removal of the thyroid can be done safely in the second trimester of pregnancy.
What is the treatment for thyroid nodules and cancer?
The treatment of thyroid nodules depends on whether these nodules are malignant (cancer) or not. Surgery to remove thyroid may be needed if:
* one or more nodules are malignant or suspected of malignancy; or
* they grow too fast or
* there are also suspicious lymph nodes in the neck
Surgery in the second trimester is considered safer, however women who want to avoid surgery during pregnancy can wait after childbirth as most types of thyroid cancer progress very slowly and a slight delay in surgical removal does not affect significantly the prognosis. Treatment of thyroid cancer often includes treatment with radioactive iodine to destroy any thyroid residual after surgery. Women who are pregnant or breastfeeding, cannot undergo such treatment.
There is no evidence that pregnancy causes cancer recurrence in women who were successfully treated in the past. If a woman has a history of thyroid cancer and has been treated with radioactive iodine in the past, she should wait a 12-month period before becoming pregnant safely.
