SCREEN, CONFIRM, AND START TREATMENT INSIDE THE FIRST TWO WEEKS
Congenital Hypothyroidism - StatPearls (NCBI Bookshelf NBK558913) - https://www.ncbi.nlm.nih.gov/books/NBK558913/
The whole value of this diagnosis is in its timing. The baby usually looks normal, the screening test finds it, and the intellectual outcome depends on treatment starting before the second week of life. So the primary-care job is to make sure the heel-prick was done, chase the result, and get the confirmatory thyroid function test and the first dose arranged without waiting for a clinic slot.
- THE BABY LOOKS WELL - a newborn with congenital hypothyroidism frequently has no symptoms at all, and it is the newborn screen (NBS) that finds them. There is no examination finding to wait for. A normal-looking newborn does not exclude it and never has.
- TIME THE HEEL-PRICK - the screen is best taken somewhere between 2 and 4 days of life; failing that, take it before the baby leaves hospital. A sample taken too early misleads: where a baby went home early and the screen was taken inside the first 24 hours, the TSH may read high simply because it surges after delivery in response to the cold. That is a false positive, and it means screening a second time.
- TREAT BEFORE TWO WEEKS - screening programmes, and starting L-T4 before 2 weeks of life, are what prevent intellectual damage and give the best neurodevelopmental result. Start early enough and at a large enough dose - before the 2nd week - and global intelligence comes out where it should. This is the whole reason the pathway is urgent.
- THE DECISION RESTS ON THE BLOOD TEST, NOT ON A SCAN - imaging is not advised routinely, because what it shows changes nothing about the treatment. What decides whether therapy starts is the abnormal thyroid function test, and nothing else. Do not let a waiting list for an ultrasound or an uptake scan delay the first dose.
- A PREMATURE BABY'S RESULT IS HARDER TO READ - a preterm infant may have the hypothyroxinaemia of prematurity: a low free T4 with a normal TSH, from a hypothalamic-pituitary-thyroid axis that has not matured. Most such babies have normal thyroid function by 6 to 10 weeks. Repeat rather than treat or dismiss on one abnormal preterm sample.
- EXAMINE FOR THE THINGS THAT TRAVEL WITH IT - other congenital malformations turn up more often in these children: cardiac ones above all, septal defects among them, along with renal abnormalities, and a raised risk of neurodevelopmental disorder. Examine the baby thoroughly, and include a hearing screen.
- IODINE CUTS BOTH WAYS - too much iodine can cause it, and so can too little, in a baby born where goitre is endemic or iodine is scarce. Ask what was applied to the mother's skin or the cord, and what the family's salt is.
- TELL THE PARENTS WHY THE FOLLOW-UP MATTERS - the parents need to understand what congenital hypothyroidism is, and why treating it early and at the right dose is what keeps the child's development on course. A family who stop the syrup when the baby "seems fine" is the commonest way this goes wrong.