- Pregnant mothers with detectable thyroid autoantibodies and normal thyroid function are at an increased risk for miscarriage and for postpartum thyroid disease,
- Pregnant mothers with thyroid hormone deficiency or TSH elevation during pregnancy may have children at risk of mild impairment in their intellectual function and motor skills, and
- Pregnant women being treated with thyroid hormone replacement often require a 30-percent to 50-percent increase in their thyroid hormone dose.
P. Reed Larsen, MD, a Professor of Medicine at Harvard Medical School and Chief of the Endocrinology Division at Brigham & Women’s Hospital in Boston, asserted that there is not yet data that backs up the need for population-wide screening; however, he emphasized that the "threshold should be low for identifying at-risk women for screening. These factors include women who have a family or personal history of thyroid disease, goiter, diabetes, history of miscarriage, or symptoms suggesting hypothyroidism." The ATA also makes this assertion.
As for women who have known hypothyroidism before conception, Dr. Larsen strongly advised that physicians should provide pre-pregnancy counseling about the risks and changes in therapy that are needed. It is also important that these women have their thyroid hormone levels – TSH, in particular – checked as soon as pregnancy is confirmed. He and his colleagues have shown that many of these women will need to increase their thyroxine replacement as much as 50 percent in the first trimester.
"With these steps, as well as careful monitoring of TSH, we should be able to maintain normal thyroid hormone availability to the fetus during this critical period of development before fetal thyroid maturation occurs," added Dr. Larsen.
John H. Lazarus, MA, MD, Professor of Clinical Endocrinology at the University of Wales College of Medicine, Llandough Hospital in Cardiff, Wales, United Kingdom, added that there is substantial evidence from both retrospective and prospective studies suggesting that early gestational low maternal circulating thyroxine – a thyroid hormone, also known as T4 – concentrations adversely affect neonatal and child development at least to age 7.
Acknowledging the current lack of clinical trial data, he presented preliminary information about a current randomized, prospective study called CATS (Controlled Antenatal Thyroid Screening), which aims to ascertain if screening for thyroid function in early pregnancy is justified. The study plans to enroll 22,000 women when they are less than 16 weeks gestation and will look at whether treating thyroid disorders with thyroxine therapy during pregnancy can prevent adverse outcomes. Following delivery, the children will be tested with appropriate psychological evaluation at ages 2 and 5.
Paul Ladenson, MD, Director of the Division of Endocrinology and Metabolism at Johns Hopkins Medical School in Baltimore reviewed the benefits and costs of identifying pregnant women at risk of hypothyroidism. He concluded that "gestational hypothyroidism probably occurs with a significant incidence; TSH testing can diagnose the condition and thyroxine can treat it; and maternal and fetal consequences appear to be clinically significant based on anecdote and small clinical trials, and reversibility could be predicted." However, he added, "Evidence from definitive prospective, randomized clinical trials is lacking, and the cost of this new preventive medical intervention would be substantial."
" While most of the experts agreed that current scientific data falls short of supporting immediate widespread population screening for thyroid disease and thyroid autoimmunity," said Gregory Brent, MD, of the UCLA School of Medicine and the ATA Secretary, "there is sufficient information to recommend some interim measures and guidance for additional data that is required to design an effective screening program."
The ATA statement includes a "plan for action" that calls on governmental institutions, such as the Centers for Disease Control and Prevention; professionals organizations, such as the ATA and AACE; and nongovernmental groups, such as the March of Dimes, to implement a coordinated program of patient education, practice review, and research on the impact of maternal thyroid status on pregnancy and fetal and childhood development.
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More information on the ATA statement and guidelines is available online.
For more information on having a safe pregnancy with thyroid antibodies or thyroid conditions, read the Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success
