Hypothyroidism During Pregnancy (cont.)
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.
Next: Hypothyroidism During Pregnancy At A Glance »
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