Of all the conditions a paediatric endocrinologist treats, congenital hypothyroidism is the one where timing changes a life most decisively, and where a simple test, done in the first week, does almost all of the work.
What the test is looking for
Roughly one baby in every 1,000 to 1,500 in India is born with a thyroid gland that is missing, misplaced or unable to make enough thyroid hormone. The incidence here is higher than in many Western populations.
Thyroid hormone is essential for brain development in the first months of life. A baby with untreated congenital hypothyroidism looks entirely normal at birth, and this is the crucial point, because they were supplied by their mother’s thyroid hormone across the placenta. The visible signs appear over weeks to months, by which time irreversible damage to brain development has begun.
Treated within the first two to four weeks with a daily tablet, the same baby has an essentially normal developmental outcome. There are very few interventions in medicine with that ratio.
How it is done
A few drops of blood from the baby’s heel, on to a filter paper card, ideally at 48 to 72 hours of age, after the normal newborn TSH surge has settled, before discharge if possible.
Screening in India is not yet universal. It is government-mandated in some states and offered by most private hospitals, but plenty of babies still leave hospital without it.
An abnormal screen is not a diagnosis
This is the part that causes the most distress, so it is worth being clear.
A screening test is deliberately set to catch every affected baby, which means it also flags babies who turn out to be fine. A raised screening TSH means one thing: a confirmatory test is needed, quickly.
Confirmation is a venous sample for TSH and free T4. If those are abnormal, treatment begins, usually the same day the result arrives. Imaging to determine the cause (an ultrasound, sometimes a thyroid scan) is useful but must never delay starting treatment.
What treatment involves
Levothyroxine, once a day, by mouth. The tablet is crushed and given in a small amount of water or breast milk on a spoon.
Some practical points that matter more than they sound:
- Give it on an empty stomach, roughly 30 minutes before a feed where feasible.
- Do not mix it into soy formula, iron drops or calcium, all of which reduce absorption. Space them apart by a few hours.
- Never adjust or stop the dose based on how the baby seems. Thyroid dosing is guided by blood tests only.
- Monitoring is frequent at first, every two to four weeks initially, then progressively less often as levels settle.
- Babies grow fast, and the dose changes with them. This is expected, not a sign that anything has gone wrong.
Around the age of three, when the critical window for brain development has passed, some children with a normally positioned gland are given a supervised trial off treatment to see whether the hypothyroidism was transient. A meaningful minority turn out not to need lifelong therapy.
The signs to know
If screening was missed or unavailable, these are the features that should prompt a thyroid test in an infant:
- Prolonged jaundice beyond two weeks
- Constipation, poor feeding, unusual sleepiness, the “such a good baby, never cries” pattern
- A large tongue, a hoarse cry, cold and mottled skin
- An umbilical hernia
- A large anterior fontanelle, or a posterior fontanelle still open
- Poor weight gain or slow growth
Any one of these alone is common and usually innocent. Several together deserve a test the same week.
The one thing to take away
If you have a newborn: ask whether the heel-prick screen was done, and ask for the result. Do not assume it was done because you were in a hospital, and do not assume no news is good news.
If you have a baby already on levothyroxine: give it every single day, keep the follow-up appointments, and know that the outlook, with treatment started early and maintained properly, is excellent.
General information. Any concern about a newborn’s thyroid should go to your paediatrician promptly.