In addition, the ATA statement called for prospective studies looking at population screening and treatment of asymptomatic -- or subclinical –- hypothyroidism, also known as an underactive thyroid. The organization of thyroid specialists also proposes public education initiatives, including messages about maternal thyroid health in over-the-counter pregnancy test kits.
The April 2, 2004 symposium in Alexandria, VA, titled "The Impact of Maternal Thyroid Status on Pregnancy and Fetal and Childhood Development," brought together top researchers and clinicians in obstetrics and gynecology, neonatology, and thyroid diseases to explore important clinical and policy issues to educate caregivers about the best diagnosis, treatment, and monitoring strategies as well as public policy issues that influence how care is provided.
According to Stephen LaFranchi, MD, of the Oregon Health & Science University in Portland, Ore., a co-chair of the symposium:
Maternal hypothyroidism and autoimmune thyroid disease – like Hashimoto's thyroiditis, a type of hypothyroidism, or underactive thyroid – increase the risk of pregnancy complications, such as miscarriage, prematurity, gestational hypertension, and pre-eclampsia, as well as deficits of intellectual development in children. The symposium tackled many unresolved issues, such as whether it is time to consider pilot screening programs of women for maternal hypothyroidism as a preventive measure, just as we screen newborns for congenital hypothyroidism to prevent the condition’s harmful effects.The experts described why maternal thyroid hormone is so important to the developing fetus. Gabriella Morreale de Escobar, MD, of the Instituto de Investigaciones Biomedicas, "Alberto Sols," in Madrid, Spain, explained that the fetus depends solely on the mother in the first half of gestation for thyroid hormone, especially thyroxine, needed for the developing brain. She added that pregnant women who are underproducing thyroxine are, therefore, at risk of having children with lower IQs and learning problems, such as attention-deficit hyperactivity disorder (ADHD), whether or not their circulating thyroid-stimulating hormone (TSH) concentrations are increased.
The most frequent cause of the inability of the maternal thyroid to produce enough thyroxine for fetal brain development is an inadequate supply of iodine. Amounts of this micronutrient, a necessary component of thyroid hormone, are needed with the onset of pregnancy and are almost double those needed by children and non-pregnant adults. "Intellectual impairments of many children could be easily prevented by promoting the use of iodine supplements taken before pregnancy throughout gestation and lactation," Dr. Morreale said.
The ATA statement concurs, emphasizing that pregnant and nursing women should take daily vitamin supplements that contain iodine, at least 220 micrograms a day for pregnant women and 290 micrograms daily for lactating women. Experts caution that only 35% of prenatal vitamins contain iodine. Worldwide, iodine deficiency remains the major factor responsible for intellectual impairment, although, in the United States, says the ATA statement, iodine nutrition is adequate. Even so, the statement goes further to say that new data indicate that some American women of reproductive age may be at risk for slightly deficient intake. Furthermore, the ATA believes there is a need for research to clarify the iodine nutrition status of pregnant women in the United States, including measuring iodine levels in breast milk and correlating with maternal iodine nutrition and factors such as smoking.
The effect of environmental agents on thyroid function and iodine nutrition was another important topic discussed at the symposium. R. Thomas Zoeller, PhD, Professor of Biology at the University of Massachusetts in Amherst, said that ammonium perchlorate (a contaminant in some water supplies) is known to reduce the ability of the body to use existing iodine. Moreover, PCBs (polychlorinated biphenyls) are known to influence thyroid function and thyroid hormone action, which can alter iodine uptake during pregnancy and lactation. PCBs also appear to influence thyroid hormone action in tissues, including the developing brain. Thiocyanates in cigarette smoke are as a negative factor as well. "Chemicals in the environment can affect thyroid function in the mother and fetus and thyroid hormone ‘signaling action’ in the developing brain," concluded Dr. Zoeller.
Another potential problem related to hypothyroidism was described at the symposium by Daniel Glinoer, MD, PhD, who heads the Thyroid Investigation Clinic & Endocrine Section at the University Hospital Saint Pierre in Brussels, Belgium. "Five percent to 8% of women carry thyroid autoantibodies," he stated. These autoantibodies are strongly linked to the occurrence of miscarriage as well as a condition that occurs after delivery, called post-partum thyroiditis. Symptoms include depression, fatigue, and difficulty nursing. "Subclinical hypothyroidism – when the person has no visible symptoms and the condition is only detectable through laboratory tests – is often undiagnosed, and the severity of hypothyroidism increases with gestational time." He estimated, "Five percent to 10% of the young female population could be affected, which has negative public health consequences.” Dr. Glinoer also discussed hyperthyroidism – an overactive thyroid – explaining that it is “relatively uncommon in pregnancy but can be severe if untreated."