Risks to the Baby in a Hashimoto's Pregnancy
Can this Autoimmune Thyroid Condition Harm Your Baby?
Jun 9, 2009
Women with Hashimoto's autoimmune thyroiditis often find that their condition improves during pregnancy, due to the change in the status of their normally-overactive immune condition. But any hypothyroid symptoms are a threat to the baby’s wellbeing, and thyroid function testing is essential at every trimester.
How Pregnancy Affects the Thyroid
Even normal, fully-functioning thyroids are affected by pregnancy. This is because two hormones that are closely associated with pregnancy also affect the thyroid: human chorionic gonadotropin (hCG) and estrogen.
- HCG is the hormone that is measured in the pregnancy test. It has a low-level thyroid-stimulating activity, and so as levels rise during the first trimester, the body slightly lowers its level of TSH (it “thinks” it doesn’t need as much of the Thyroid Stimulating Hormone, as it seems to already be stimulated). This situation leads to a condition of lower TSH but raised Free T4 levels (1) during the first trimester, but all hormone levels return to normal for the second and third trimesters.
- The second important hormone is estrogen, the main female hormone. This increases the total thyroid hormone levels in the blood (because it increases the amount of thyroid hormone-binding proteins in the serum, and >99% of the thyroid hormones in the blood are bound to these proteins). But the levels of ‘free’ or active hormones (Free T4 and Free T3) usually remain normal, as the free hormones are not bound to proteins.
In other words, in a normal pregnancy, the thyroid is considered to be functioning properly if the TSH, Free T4 and Free T3 remain at normal, healthy levels.
However, women with Hashimoto’s may enter a pregnancy with almost any level of thyroid hormones: some may have normal TSH and T4, T3 readings but high antiperoxidase antibody levels, while others may have raised TSH and lowered T4 and T3. It’s important to know where the levels stand as soon as you are pregnant, so any changes can be modified and treated. (Read more about how the thyroid works)
Does the Thyroid Itself Change During a Normal Pregnancy?
The thyroid gland can increase in size during an otherwise problem-free, healthy pregnancy, but this tends to occur more frequently in iodine-deficient areas of the world. A goitre is also very often a symptom of autoimmune thyroiditis, and this can cause concern to a mother-to-be who also has Hashimoto’s disease. However, in Hashimoto’s the goitre is likely to be due to the autoimmune nature of the disease, rather than an iodine deficiency, and is therefore unlikely to pose the same kind of risk as those due to iodine deficiency. It is advisable, though, to have any goitre thoroughly checked before becoming pregnant if you have Hashimoto’s, because the disease can cause a problem with iodine uptake (too much or too little), and this would impact on the pregnancy and the baby’s development if it remains untreated.
Why is Iodine Important?
The baby is completely dependent on the mother for the production of thyroid hormone during the first trimester, after which the baby’s thyroid begins to produce thyroid hormone on its own. But even then the baby continues to depend on the mother for iodine (in order to make the thyroid hormones). During pregnancy women need about 250 micrograms (μg) of iodine a day, and it is important that this is correctly utilized within the mother’s body, so women with Hashimoto’s need to be sure that their treatment is correct during the time they are pregnant.
Thyroid hormone is critical for a baby’s brain development. Children born with no thyroid function at birth (congenital hypothyroidism) can have severe cognitive, neurological, and developmental abnormalities if the condition is not recognized and treated promptly – but many of these developments can be avoided with prompt treatment. Most developed countries (including the US) routinely screen babies for congenital hypothyroidism immediately after birth.
How Else is the Baby Affected if the Mother has Hashimoto’s?
Anyone with a hypothyroid condition is more likely to experience problems in becoming pregnant than people with a normal-functioning thyroid, and risks suffering recurrent miscarriages. Untreated hypothyroidism of all sorts increases the risk of coronary artery disease, as it is closely associated with a prevalence of lipid disorders. In women with Hashimoto’s, this is most likely to emerge as antiphospholipid syndrome; this is easily tested, and the dangers overcome by simple aspirin and Heparin treatment. Untreated, it can cause blood-clotting problems as the placenta develops, and later complications such as premature birth, and low birthweight.
Other risks to the baby mirror those of any hypothyroid condition, and include placental abruption and pre-eclampsia (pregnancy-induced hypertension). Mild brain developmental abnormalities may also occur in children born to women with untreated hypothyroidism for reasons other than iodine deficiency (see above), so any form of hypothyroidism must be identified and treated. The key advice seems to be “test and test again” to make sure any variation in thyroid levels is accounted for, and the baby receives all the iodine necessary.
What Tests Should I Have if I’m Pregnant and Have Hashimoto’s?
If you have Hashimoto’s and wish to become pregnant, make sure your treatment is adequate pre-pregnancy; test again once pregnant, and then again every 8–10 weeks during the pregnancy. Discuss the appropriate number of scans with your physicians after making them aware of your condition; some doctors prefer to take regular scans throughout the pregnancy. Antiphospholipid syndrome can be diagnosed by testing for lupus anticoagulant (LAC) and anticardiolipin (aCL) antibodies.
References
- Management of high-risk pregnancy”, Queenan & Spong, Wiley-Blackwell, 2007.
- The National Endocrine and Metabolic Diseases Information Service (USA), Pregnancy and Thyroid Disease
- The American Thyroid Association, “Thyroid Disease and Pregnancy”, Patient Brochure 2008.
- Journal of Medical Screening, November 2000.
