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Low Thyroid Level in Newborns: New Clues on How Long to Treat

Some babies born with congenital hypothyroidism may need lifelong treatment to support normal growth and development but others will likely outgrow the condition.

With Carole Saba, MD, and Luis Gonzalez-Mendoza, MD

When a baby is born with abnormally low thyroid function, known as congenital hypothyroidism (CH), parents are understandably worried. Normal thyroid hormone levels are needed to assure that growth and develop occur normally and that the heart, muscles and other organs are working correctly.

Once parents hear the diagnosis, they all have the same question, says  Carole Saba, MD, a pediatric endocrinologist at Publique-Hopitaux de Paris, the Robert Debre University Hospital in Paris, France. "The main question is, how long do we treat?"

The newborn who has abnormally low thyroid levels (measured by a blood test 1 to 2 days after birth) is easily treated with the most common form of supplemental thyroid hormone, levothyroxine, in tablet form.

Researchers have new insights to care for babies born with low thyroid function.

More than Half of Babies Born Hypothyroid Grow Out of It

Some children will need lifelong treatment, while others require only short-term hormone supplementation. Figuring out which child has transient congenital hypothyroidism and who has the permanent hormone condition is the ongoing question.

To address this clinical concern, Dr. Saba and her team evaluated 92 children at age 3 who were diagnosed with congenital hypothyroidism at birth. All the toddlers had an anatomically normal thyroid when they were born in Paris between 2002 and 2012.2 All were treated with levothyroxine.

The researchers found that more than half the children no longer had a low thyroid level by the time they turned 3 years of age; these toddlers were determined to have a transient (short-term) form of the condition.1 The thyroid hormone levels in these babies had normalized so the doctor was able to discontinue the levothyroxine supplementation.

At the median age of 18 months, this proved the midpoint for babies needing levothyroxine replacement therapy—with half of them no longer needing the hormone above this age, and the other half stopping the medication even earlier).1

Predictors of Transient Congenital Hypothyroidism

Children who had the lower increases in their blood levels of thyroid stimulating hormone (TSH)—which controls thyroid gland activity—when diagnosis at birth, were more likely to outgrow the condition,1 the researchers found.

TSH tells the thyroid gland how much hormone to produce so if levels are high, it is an indication of hypothyroidism. Those who no longer had the hypothyroidism were also more likely to need lower doses of levothyroxine initially and again at 6 and 12 months.1 These babies were also less likely to have a hereditary or genetic form of this hypothyroid condition

While the usual routine generally is to treat children until they reach 3 years of age because the time to that point is very important for brain development, Dr. Saba says her findings suggest that it may not be necessary to continue treatment out that long in every baby, and that treatment may often be safely stopped at six months, based on the blood test results for the thyroid levels. She cites the benefits of potential cost savings in being able to stop the levothyroxine sooner whenever possible.

Luiz Gonzalez-Mendoza, MD, pediatric endocrinologist and director of the division of endocrinology at Nicklaus Children's Hospital in Miami, Florida who was not involved, reviewed the study findings for EndocrineWeb, and recommended a bit of caution.

Congenital Hypothyroidism is Very Manageable 

It is better to err on the side of caution, said Dr. Gonzalez-Mendoza. He says he has noticed some predictors of transient congenital hypothyroidism in his own practice.

“Typically, as a child with this condition grows, the dose of levothyroxine has to be adjusted to maintain normal blood levels of thyroid hormone. If that [correction] does not happen, then it usually means the condition is transient," he tells EndocrineWeb.

What Do Parents Need to Know about Hypothyroidism in Newborns?

When they first hear the diagnosis, ''parents are usually upset," he says. They tend to calm down when he explains that congenital hypothyroidism is really very easy to treat. “Parents simply need to crush the tablet and mix into breast milk or add to formula once a day to treat the child,” he says.

Most babies have no obvious signs or symptoms of low thyroid levels at birth. Some may have either at birth or soon after, a puffy face, a hoarse cry, a large and thick tongue, or a distended stomach.2

Left untreated, hypothyroidism in babies can lead to ''all sorts of neurological issues and mental deficits," he says. Dr. Gonzalez-Mendoza tells parents that treatment is critical to prevent cognitive loss and developmental delays.

That's why the blood test to screen for congenital hypothyroidism is done within 48 hours of birth, he says; sooner will not give valid results. Sometimes, if the initial blood test is not definitive, the test may be repeated to confirm the presence of congenital hypothyroidism, he says.

In the US, it is common for pediatricians to treat newborns who have been diagnosed as having hypothyroidism with levothyroxine until they are two or three years old. During treatment and after, patients are monitored to check that their blood levels of thyroid hormone remain in the normal range, especially if the levothyroxine is stopped; as such, the baby’s blood levels will guide treatment decisions, says Dr. Gonzalez-Mendoza says.

Neither Dr. Saba nor Dr. Gonzalez-Mendoza has any relevant financial conflicts.