15/07/2014
HYPOTHYROIDISM IN PREGNANCY
Hypothyroidism in the mother and/or the unborn baby can have significant adverse health effects on the unborn baby, and so maternal hypothyroidism should be avoided.
If a woman is diagnosed with hypothyroidism prior to pregnancy, her thyroid medication should be adjusted so that the TSH level is no higher than 2.5 µU/ml prior to becoming pregnant.
If a woman is diagnosed as hypothyroid during pregnancy, she should be treated without delay, with the goal of restoring her thyroid levels to normal as quickly as possible. During the first trimester, the TSH should be maintained at less than 2.5 µU/ml (and less than 3.0 µU/ml in the second and third trimesters.) After initial diagnosis, thyroid function tests should be reevaluated within 30 to 40 days.
By the time a woman is four to six weeks pregnant, her dose of thyroid medication will usually need to be increased, potentially by as much as 30 to 50 percent.
A woman with thyroid autoimmunity (such as she has previously tested positive for thyroid antibodies) who has normal TSH levels in the early stages of her pregnancy is still at risk of becoming hypothyroid at any point in the. She should be monitored regularly through the pregnancy for elevated TSH.
Subclinical hypothyroidism – a TSH level above normal, with normal free T4 levels – is associated with negative health outcomes for both the mother and baby. Treatment of the mother has been shown to help ensure a healthier pregnancy. Treatment has not, however, been proven to affect the baby’s long-term neurological development. The experts believe that the potential benefits of treatment do outweigh any potential risks, however, and recommend treatment in women with subclinical hypothyroidism.
After childbirth, most women with hypothyroidism will need their dosage of thyroid hormone replacement reduced.
All pregnant women with hyperemesis gravidarum (severe morning sickness that includes substantial weight loss and dehydration) should have their thyroid function evaluated.
Overt hyperthyroidism due to Graves’ disease, and gestational hyperthyroidism with significantly elevated thyroid hormone levels -- free T4 above the reference range and TSH < 0.1 µU/ml -- and may require treatment.
Normal TSH Levels DURING PREGNANCY
According to research, during a normal pregnancy, the following are the TSH normal ranges for an iodine-sufficient population without autoimmune antibodies...
First Trimester: 0.24 - 2.99
Second Trimester: .46-2.95
Third Trimester: .43 - 2.78
Women who are on thyroid hormone replacement should plan to increase their dosage by 30% to 60% during the first few weeks of pregnancy, and ultimately are likely to need to have their thyroid hormone dosage increased by as much as 50% during pregnancy.
How does pregnancy normally affect thyroid function?
Two pregnancy-related hormones—human chorionic gonadotropin (hCG) and estrogen—cause increased thyroid hormone levels in the blood. Made by the placenta, hCG is similar to TSH and mildly stimulates the thyroid to produce more thyroid hormone. Increased estrogen produces higher levels of thyroid-binding globulin, a protein that transports thyroid hormone in the blood. These normal hormonal changes can sometimes make thyroid function tests during pregnancy difficult to interpret.
Thyroid hormone is critical to normal development of the baby’s brain and nervous system. During the first trimester, the fetus depends on the mother’s supply of thyroid hormone, which it gets through the placenta. At 10 to 12 weeks, the baby’s thyroid begins to function on its own. The baby gets its supply of iodine, which the thyroid gland uses to make thyroid hormone, through the mother’s diet.
Women need more iodine when they are pregnant—about 250 micrograms (μg) a day. In the United States, about 7 percent of pregnant women may not get enough iodine in their diet or through prenatal vitamins.1 Choosing iodized salt—salt supplemented with iodine—over plain salt is one way to ensure adequate intake.
The thyroid gland enlarges slightly in healthy women during pregnancy, but not enough to be detected by a physical exam. A noticeably enlarged gland can be a sign of thyroid disease and should be evaluated. Higher levels of thyroid hormone in the blood, increased thyroid size, and other symptoms common to both pregnancy and thyroid disorders—such as fatigue—can make thyroid problems hard to diagnose in pregnancy.
How does hypothyroidism affect the mother and baby?
Some of the same problems caused by hyperthyroidism can occur in hypothyroidism. Uncontrolled hypothyroidism during pregnancy can lead to
• congestive heart failure
• preeclampsia
• anemia—a disorder in which the blood does not carry enough oxygen to the body’s tissues
• miscarriage
• low birthweight
• stillbirth
Because thyroid hormones are crucial to fetal brain and nervous system development, uncontrolled hypothyroidism—especially during the first trimester—can lead to cognitive and developmental disabilities in the baby.
How is hypothyroidism in pregnancy diagnosed?
Like hyperthyroidism, hypothyroidism is diagnosed through a careful review of symptoms and measurement of TSH and T4 levels.
Symptoms of hypothyroidism in pregnancy include extreme fatigue, cold intolerance, muscle cramps, constipation, and problems with memory or concentration. High levels of TSH and low levels of free T4 generally indicate hypothyroidism. Because of normal pregnancy-related changes in thyroid function, test results must be interpreted with caution.
The TSH test can also identify subclinical hypothyroidism—a mild form of hypothyroidism that has no apparent symptoms. Subclinical hypothyroidism occurs in two to three of every 100 pregnancies.4 Test results will show high levels of TSH and normal free T4. Experts have not reached a consensus as to whether asymptomatic pregnant women should be routinely screened for hypothyroidism. But if subclinical hypothyroidism is discovered during pregnancy, treatment is recommended to help ensure a healthy pregnancy.
How is hypothyroidism treated during pregnancy?
Hypothyroidism is treated with synthetic thyroxine, which is identical to the T4 made by the thyroid gland. Women with pre-existing hypothyroidism will need to increase their prepregnancy dose of thyroxine to maintain normal thyroid function. Thyroid function should be checked every 6 to 8 weeks during pregnancy. Synthetic thyroxine is safe for the fetus and necessary for its well-being if the mother has hypothyroidism.
Points to Remember
• Pregnancy causes normal changes in thyroid function but can also lead to thyroid disease.
• If uncontrolled during pregnancy, hyperthyroidism—too much thyroid hormone in the blood—can be dangerous to the mother and cause health problems such as congestive heart failure and poor weight gain in the baby.
• Mild hyperthyroidism in pregnancy does not require treatment. More severe hyperthyroidism is usually treated with drugs that interfere with thyroid hormone production.
• If uncontrolled during pregnancy, hypothyroidism—too little thyroid hormone in the blood—also threatens the mother’s health and can lead to developmental disabilities in the baby.
• Hypothyroidism in pregnancy is safely and easily treated with synthetic thyroid hormone.
• Postpartum thyroiditis—inflammation of the thyroid gland—causes a brief period of hyperthyroidism, often followed by hypothyroidism that usually resolves within a year. Sometimes the hypothyroidism is permanent.
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DR AMITABH KHANNA
• SENIOR CARDIODIABETOLOGIST
ROCKLAND HOSPITAL,DWARKA
ARTEMIS HOSPITAL,DWARKA
• FOUNDER PRESIDENT, IMA DWARKA
• PRESIDENT,DWARKA DIABETE ASSOCIATION
