What is Congenital Hypothyroidism?
Congenital hypothyroidism (CH) is a condition where a baby is born with a shortage of thyroid hormones. Prompt diagnosis is crucial, as delayed treatment could lead to lifelong harm to the nervous system. CH used to be a major cause of preventable intellectual disability in newborns, but newborn screening programs have resulted in earlier identification and treatment, thereby improving children’s development.
The thyroid hormones play a critical role in the body’s energy usage, growth, and nervous system development. These hormones affect brain cell growth, the development of connections between nerve cells, and the process of coating nerve cells with myelin in both unborn babies and newborns. Thyroid hormones are made from amino acids and are produced by the thyroid gland when stimulated by the thyroid-stimulating hormone (TSH) from the pituitary gland. TSH’s production is controlled by the thyrotropin-releasing hormone (TRH) from the hypothalamus, forming a feedback loop known as the hypothalamic-pituitary-thyroid (HPT) axis.
The two main thyroid hormones are thyroxine (T4) and triiodothyronine (T3), both produced by the thyroid gland. However, most circulating T3 comes from the transformation of T4 in other parts of the body. This change is caused by a set of enzymes. Both T4 and T3 can suppress TSH production, either by acting directly on the pituitary gland or indirectly by reducing the production of TRH. Other factors that inhibit TSH production include glucocorticoids, somatostatin, and dopamine. Both T4 and T3 are tightly bound to proteins in the blood, except for a small proportion of “free” T4 and T3, which are biologically active.
What Causes Congenital Hypothyroidism?
Congenital hypothyroidism (CH), or low thyroid hormone levels from birth, can come from several causes. It can either stem from problems with the development or functioning of the thyroid gland itself (primary CH) or issues related to the pituitary gland or hypothalamus — the parts of the brain that manage the thyroid (central CH).
Primary CH accounts for most of these cases, with about 80% of them arising from a failure in the thyroid gland’s development, a condition known as thyroid dysgenesis. This issue can manifest in the lack of thyroid gland formation (agenesis), misplaced gland (ectopic), or underdeveloped gland (hypoplastic). Usually, thyroid dysgenesis happens sporadically and isn’t inherited. However, genetic mutations linked to thyroid gland development can sometimes be found in 2-5% of the cases.
Aside from the genetic issues leading to permanent CH, this disease may also be temporary. For example, if a pregnant mother takes anti-thyroid drugs like methimazole or propylthiouracil, or if she has thyroid-blocking antibodies from an autoimmune thyroid disease, her baby may be born with temporary CH. Other situations, like lacking or having too much iodine, could also contribute to it. Low iodine intake is particularly an issue worldwide, especially in areas where iodine is not readily available. Likewise, exposure to substances with high iodine contents — like certain antiseptics or medical imaging agents — could harm a newborn’s thyroid creating temporary CH due to the Wolff-Chaikoff effect, a process that slows down thyroid hormone production in high-iodine situations.
Central CH, the type arising from brain-related issues affecting the thyroid, is relatively rare. It usually results from abnormalities in the pituitary gland or hypothalamus, where it is referred to as secondary or tertiary hypothyroidism.
Risk Factors and Frequency for Congenital Hypothyroidism
Congenital hypothyroidism (CH), a condition present at birth, varies in occurrence worldwide. It’s typically seen in about 1 out of every 3,000 to 4,000 newborns. Certain ethnicities have higher rates – for example, 1 in 1,600 in Hispanic babies and 1 in 2,380 in Asian babies. In contrast, it’s less common in black babies – about 1 in 11,000.
Furthermore, this health condition is more prevalent in girls than in boys, with ratios of 1.5 or 2 to 1. Other groups with higher incidence rates include twins, multiple births, babies born to older mothers, and preterm infants. Over recent years, the rate of CH seems to have doubled to 1 in 2,000 according to some newborn screening programs in the U.S. and other parts of the world.
This increase in CH occurrence is thought to be due to multiple factors. These may include a change in how we screen for the disease (now detecting milder cases), shifts in ethnic demographics such as more Asian and Hispanic births, and increased screening among babies born prematurely or with low weight.
- Congenital hypothyroidism is generally seen in 1 out of every 3,000 to 4,000 newborns.
- It is more common in Hispanic (1 in 1,600) and Asian infants (1 in 2,380), and less common in black infants (1 in 11,000).
- Girls are more likely to have it than boys, with a ratio of 1.5 or 2 girls for every boy.
- The condition is also more common in twins, multiple births, babies born to older mothers, and premature babies.
- Recently, the detected rate of CH seems to have doubled to 1 in 2,000.
- Factors contributing to this increase may include improved screening practices, changes in ethnic population distribution, and more screening of low-birth-weight or premature infants.
Signs and Symptoms of Congenital Hypothyroidism
Newborns with a condition called congenital hypothyroidism (CH) may show little or no symptoms when they are born. This happens because expecting mothers share some of their thyroid hormone with their babies before they are born. However, as the baby grows, the signs of this condition become more noticeable.
During the early stages, which can become noticeable in the first few weeks of the child’s life, the baby might show signs like:
- Feeling tired
- Low muscle tone
- Large soft spots on the head
- Difficulty feeding
- Extended periods of jaundice
- Weak or horse-sounding cry
- Constipation
- Low body temperature
Usually, after about six weeks, they could display other symptoms, which include:
- Changes in facial features with a lowered nasal bridge
- Puffy eyelids
- Large tongue
- Coarse hair
- Thick, dry and cold skin that might look blotchy
- Swollen abdomen
- Umbilical hernia
- Reduced reflexes
- Slow heart rate
- Low blood pressure
- Anemia
In some cases, respiratory distress may occur due to swelling of the airway. This can be identified by noisy breathing, a stuffy nose and intermittent bluish discoloration around the mouth.
Testing for Congenital Hypothyroidism
Newborn babies are usually screened for congenital hypothyroidism (CH) shortly after birth. These newborn screening (NBS) tests are typically done using blood samples taken from the baby’s heel. The goal of these tests is to catch and diagnose CH early on, usually by measuring levels of thyroid-stimulating hormone (TSH). TSH tests are the most precise, while T4 tests can reveal cases of hypothalamic-pituitary-hypothyroidism, a less common form of CH. The timing of the test, the baby’s age, prematurity, and overall health can all affect the results.
It’s best to do the screening between the second and fourth day of life. If that’s not possible, it should be done before the baby leaves the hospital. There are three methods for this screening. One tests TSH first and then T4 if necessary, another tests T4 first and then TSH if needed, and the third tests both at the same time. While the third option is best, it’s also more expensive.
Sometimes, additional testing may be needed. A baby’s TSH levels can be suppressed due to several reasons, leading to a “masked” or delayed CH diagnosis. Therefore, a second round of testing is recommended particularly for premature babies, babies born with low birth weight, or those who are ill. For these babies, testing should be done multiple times until they are discharged from the hospital.
For babies who have abnormal NBS results, a follow-up blood test for TSH and free T4 is necessary. The treatment should begin immediately, regardless of the results of further tests to find the cause of CH.
There are three common outcomes from these tests. If both free T4 and TSH are high, it confirms primary hypothyroidism. If free T4 is normal but TSH is high, it suggests compensated or subclinical hypothyroidism. Lastly, when both free T4 and TSH are low, it hints at central hypothyroidism, which typically is accompanied by other hormone deficiencies.
Additional testing isn’t usually needed, but if a baby has abnormal thyroid function test results, imaging studies might help to find the cause. For example, an ultrasound can show the size and structure of the thyroid gland. A thyroid scan can show the location and size of the thyroid gland. Tests can also be done for thyroid-blocking antibodies, thyroglobulin levels, and iodine levels in urine.
Radiographs of the knees can indicate the severity of CH and help predict the baby’s future intellectual and motor development.
Treatment Options for Congenital Hypothyroidism
If a baby is born with a medical condition known as congenital hypothyroidism (CH), doctors usually start treatment with a medication named levothyroxine (or L-T4) right away. Starting the treatment early – before the baby is even 2 weeks old – can help prevent learning difficulties and support healthy mental and motor development. It’s best to use levothyroxine by itself for this treatment.
The initial dosage is tailored to how serious the case of hypothyroidism is. For severe cases, the starting dose for infants is often between 10 to 15 micrograms per kilogram per day, or 50 micrograms per day. This higher dose is particularly used for newborns who had very low T4 hormone levels before treatment. Higher starting doses of levothyroxine can bring hormone levels back to normal within 3 days, and the thyroid-stimulating hormone (TSH) levels back to normal within two weeks. After TSH is normal, the dosage is typically reduced to 37.5 micrograms per day to avoid over-treatment.
Levothyroxine is given orally, often crushed and mixed with a small amount (1 to 2 milliliters) of water or breast milk. It can be fed to the infant using a small spoon or a syringe. The medication should be given at the same time every day. It’s also better given at a different time from foods or supplements that contain calcium, iron, or soy, as these substances can interfere with the absorption of the hormone.
Doctors will generally do a repeat blood test to check thyroid hormone levels 1 to 2 weeks after starting levothyroxine. The frequency of the blood tests varies with age: every couple of weeks until TSH is back to normal, then every 1 to 3 months up to 1 year of age, every 2 to 4 months from age 1 to 3, and then every 3 to 12 months until the child’s growth is complete. More check-ups and lab tests might be necessary if there are concerns about medication adherence or if the test results are abnormal. Clearly, these regular clinic visits and blood tests are essential to make sure the dosage of levothyroxine is just right for the child’s needs.
What else can Congenital Hypothyroidism be?
Babies that leave the hospital soon after birth, typically having newborn screening tests done within the first 24 hours, might show increased levels of thyroid-stimulating hormone (TSH), a natural reaction to the cold environment outside the womb. This might give inaccurate results, making a second test necessary. The best time to conduct newborn screening for congenital hypothyroidism, a condition that affects the thyroid gland, is between the baby’s second and fourth day of life when the TSH levels would have decreased.
When considering premature babies, we might observe a situation known as ‘hypothyroxinemia of prematurity’—characterised by lower levels of free T4, a thyroid hormone, and normal TSH due to the underdeveloped Hypothalamus-Pituitary-Thyroid (HPT) axis. Reading the thyroid function test (TFT) in such cases can be tricky, as this pattern may also arise due to central hypothyroidism or further complicated by non-thyroidal illness. It’s suggested to repeat the TFT, as mentioned earlier. Most patients are expected to have a normal TFT within 6 to 10 weeks.
What to expect with Congenital Hypothyroidism
In most cases, kids with congenital hypothyroidism (CH) — a condition they are born with that affects the thyroid gland — do very well. Started early enough, usually before the second week of life, treatment can result in a child having normal intelligence levels. Despite this, minor issues with verbal skills, focus, memory, or physical development might still occur, especially in cases where the CH is severe.
The severity of CH and initial T4 thyroid hormone levels before treatment are major factors in determining whether a child might face cognitive and motor challenges. It’s been found that kids with missing thyroids tend to have a lower IQ compared to those whose thyroid gland didn’t form correctly, probably due to brain injury sustained before birth.
In cases of severe CH, a high starting dosage of L-T4 thyroid medication (10-15 mcg/kg) can speed up the normalization of TSH (a hormone stimulating the thyroid) levels in the blood. This results in a normal global IQ by the time the child is four years old, which continues into young adulthood. However, even with early treatment, kids with CH can have a slight dip in IQ compared to their siblings. This IQ difference can be reduced, to an extent, by using a higher starting dose of the medication. Importantly, this does not interfere with growth or bone development, even with the high dose.
Possible Complications When Diagnosed with Congenital Hypothyroidism
Kids with a condition known as congenital hypothyroidism (CH) are more likely to have other birth defects. These can include heart defects like problems with the wall of the heart, kidney abnormalities, and even the risk of conditions that affect the brain and nerves. It’s important for these children to have a full check-up, including a test of their hearing ability.
The Congenital Conditions Include:
- Heart abnormalities
- Kidney irregularities
- A risk of neurodevelopmental disorders
Recovery from Congenital Hypothyroidism
Babies with a condition known as congenital hypothyroidism, especially those in intensive care who cannot take medications orally due to surgical procedures or other conditions, need to be given their L-T4 therapy through an intravenous line (IV). The IV dosage is typically half to three quarters of the oral dose.
Preventing Congenital Hypothyroidism
Parents and caretakers need to understand the diagnosis of congenital hypothyroidism – an underactive thyroid at birth – and how crucial it is to start treatment early. This early treatment can help avoid negative effects on the child’s brain development. It is very important that clear instructions are given for how to administer the medication, called L-T4. Regular check-ups and blood tests to monitor the thyroid are also vital. For more resources and learning materials on this topic, the Pediatric Endocrine Society website is an excellent reference.
