In this Article

• Introduction
• What is the thyroid gland?
• What happens with thyroid disease?
• How is hypothyroidism treated during pregnancy?
• What are the consequences of hypothyroidism during pregnancy?
• How early does the mother's thyroid hormone affect the unborn baby?
• What can be done to avoid the consequences of hypothyroidism in pregnancy?
• Hypothyroidism During Pregnancy At A Glance
• Hypothyroidism During Pregnancy Glossary
• Hypothyroidism During Pregnancy Index

How early does the mother's thyroid hormone affect the unborn baby?

Before birth a baby is entirely dependent on the mother for thyroid hormone until the baby's own thyroid gland can start to function. This usually does not occur until about 12 weeks of gestation (the end of the first trimester of pregnancy). Thus, hypothyroidism of the mother may play a role early on, before many women realize they are pregnant! In fact, the babies of mothers who were hypothyroid in the first part of pregnancy, then adequately treated, exhibited slower motor development than the babies of normal mothers. However, during the later part of pregnancy, hypothyroidism in the mother can also have adverse effects on the baby, as pointed out by the research described above. These children are more likely to have intellectual impairment.

What can be done to avoid the consequences of hypothyroidism in pregnancy?

A number of medical associations and organizations have made recommendations on screening for thyroid disease. Some of the recommendations are listed below:

• All women who are planning a pregnancy should be considered for screening of thyroid disease.
  
  
• All pregnant women with a goiter (enlarged thyroid), high blood levels of thyroid antibodies, a family history of thyroid disease, or symptoms of hypothyroidism should be tested for hypothyroidism.
  
  
• In women who are borderline, or sub-clinical, hypothyroid (for example, not in the laboratory range for true hypothyroidism, but within the low normal range) and who also have positive antibodies (which may indicate an ongoing autoimmune thyroid destruction), therapy with low dose thyroid hormone at the onset of pregnancy may be beneficial.
  
  
• There is some evidence that the antibodies that may contribute to hypothyroidism can play a role in pregnancy. Data suggest that selenium supplementation may be of benefit in women with high antibody levels at the time of preconception. This should be reviewed with your doctor.
  
  
• Women who are on thyroid hormone replacement before pregnancy should also be tested to make certain that their levels are appropriate. During pregnancy, the medication dose required may increase by up to 50%. Increases may be required as early as in the first trimester.
  
  
• Dosing is dynamic during pregnancy and should be closely monitored by regular blood testing. As the pregnancy progresses, many women require higher doses of hormone replacement.
  
  
• The dosage of thyroid hormone replacement during and after pregnancy should be carefully monitored using the blood thyroid stimulating hormone (TSH) value. The laboratory ranges for normal TSH are quite wide. Most clinicians like to keep women who are pregnant and on replacement in the "hyper" end of the normal range. This usually equates to a TSH of <2.0. Many clinicians prefer TSH in the <1.0 range.
  
  
• In women with hypothyroidism before conception, most go back to their pre-pregnancy dose of thyroid hormone within a few weeks to months.

It must be stressed that these are only guidelines. The management of each woman's situation is considered individually after consultation with her physician. The benefits of treatment extend not only to pregnant women with hypothyroidism, but also to their children.

From the Doctors at MedicineNet.com

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