The Medical Director of the March of Dimes, Nancy Green, MD, discussed the guidelines issued by the American College of Obstetricians and Gynecologists (ACOG) in 2002, which she noted were based primarily on consensus and expert opinion. ACOG stated at that time that there were insufficient data to warrant routine screening of asymptomatic pregnant women for hypothyroidism. ACOG recommended that testing of thyroid function may be performed in women with a personal history of thyroid disease or symptoms of thyroid disease.
The March of Dimes, said Dr. Green, appreciates the ATA's current review of the issue, which is in consideration of whether routine maternal thyroid screening and treatment – before conception and/or in early pregnancy – improves child cognitive development. The March of Dimes is focused on this issue primarily if it helps prevent pediatric harm. In addition, the March of Dimes is currently conducting a national campaign to prevent preterm birth, a side effect of maternal hypothyroidism.
Preterm birth, as Brian M. Casey, MD, Associate Professor of Obstetrics and Gynecology at the University of Texas Southwestern Medical Center at Dallas, pointed out, is the most common recognized cause of neuropsychological dysfunction in children. After reviewing the association of subclinical hypothyroidism with preterm birth, he concluded that "Prematurity may explain some of the neurodevelopmental abnormalities associated with maternal thyroid insufficiency."
The ATA statement emphasizes this research finding, stating that "pregnant mothers with overt or subclinical hypothyroidism are at an increased risk for premature delivery."
Other important research findings highlighted by the ATA statement include –
- 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% to 50% 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% 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.
