Thyroid Disease in Pregnancy Linked to Birth Defects

Risk Is Higher

Pregnant woman holding belly, outdoors, mid section
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According to research presented at the 2001 Society for Maternal-Fetal Medicine's annual meeting, women with thyroid disease are at a higher risk of having infants who have birth defects – including abnormalities affecting the heart, kidney or brain as well as other defects, such as cleft lip and cleft palate – than previously thought.

In a prepared statement, David A. Nagey, MD, Ph.D., of Johns Hopkins University says, "We already knew that there was an increased risk of problems, mostly intellectual or developmental, in children as a result of hypothyroid pregnancies, but the link with birth defects is new and unexpected. If these results are confirmed, it could lead to routine testing of women for thyroid disease prior to pregnancy and for (heart defects) in the fetuses of women with hypothyroidism."

Typically, the problems tended to most often affect the heart, but other defects, such as kidney and nervous system problems, cleft foot and cleft palate, were more common in women who were hypothyroid during pregnancy.

Eighteen percent of the infants studied had birth defects. Among their mothers, 13 were hypothyroid during pregnancy, and 8 were hyperthyroid during pregnancy. This compares to a general rate of approximately 3% of all infants with birth defects.

The medical world did not accept these results without question. Speaking to HealthScoutNews, endocrinologist Loren Wissner-Greene indicated that large trials had shown that babies born to mothers with thyroid disease were primarily at risk of some slight developmental delays – and not major birth defects. She questioned whether the results may have been due to some other factor, and suggests that the subject warrants further research before women become too concerned.

Dr. Nagey, however, believes that his research points to several key recommendations for women with a thyroid condition:

  • women with thyroid conditions require the care of a high-risk obstetrician
  • women who are hypothyroid should give birth at a hospital that is experienced in the postnatal care of babies with the types of birth defects seen in this study

Other Implications for Patients

In addition to Dr. Nagey's recommendation that thyroid patients see high-risk obstetricians and deliver at hospitals that have specialized neonatal care capabilities, there are some other important implications.

While different doctors will suggest different points at which to have your thyroid tested, I prefer to err on the side of too often. Many obstetricians will not even want to see you until you are six to eight weeks pregnant, and that is already beyond the point at which the body's increasing demands may have caused your TSH to elevate and jeopardize your pregnancy. Personally, I suggest that you get a home pregnancy test, and test as early as possible. Get in to have your TSH, T4 and T3 tested as soon as you have a positive pregnancy test (usually around the time of your missed period – or what they would consider 4 weeks pregnant.)

When I was pregnant, I began the pregnancy at a TSH of 1.2. Some endocrinologists believe that a woman would start the pregnancy – and be maintained throughout – at the lower end of the normal range in order to ensure a better outcome. I was tested every month during the first trimester (even more frequently if you have any abnormal results), and then every six weeks or so during the remainder of the pregnancy. The only adjustments I needed were during my first trimester.

The first trimester is really one of the most critical times for frequent testing and sufficient treatment. During that first trimester, the baby's growth and development depends on the mother's ability to increase her own thyroid output. At the end of the first trimester, the baby's own thyroid becomes active and able to produce thyroid hormone on its own. This is probably why many women, myself included, find that they need to up their levels during that first trimester, but they become stabilized after the first trimester.

Note: While a high-risk obstetrician is optimal, many women with thyroid dysfunction are followed by a regular obstetrician and an endocrinologist. Endocrinologists and obstetricians tend to be the most knowledgeable about managing thyroid disease in pregnancy. Studies have shown, however, that as many as a third of all doctors are misinformed about managing thyroid disease in pregnancy, so it's crucial that you find a practitioner or team of doctors with the expertise to properly manage thyroid disease during pregnancy.

View Article Sources
  • Nagey, David, MD. Society for Maternal-Fetal Medicine Annual Meeting Statement, 2001, Online