If the maternal hypothyroidism is secondary to congenital aplasia or hypoplasia of the thyroid gland there should be no significant increased risk to the baby of hypothyroidism and Guthrie test is sufficient.

This can be secondary to:

• Hashimoto’s thyroiditis- the mother may be producing thyroid inhibiting so the baby may develop transient hypothyroidism. Transient hypothyroidism due to blocking antibodies should be picked up by the Guthrie screen.
• Thyroidectomy for cancer- the infant does not require thyroid function tests (other than routine Guthrie).
• Treatment (surgery or radioiodine) for Graves’ disease- the baby is at risk of neonatal thyrotoxicosis and will need to be managed as for maternal thyrotoxicosis.
• MEN (multiple endocrine neoplasia) then the child will require follow-up/screening, but not in the newborn period.

In maternal thyrotoxicosis or history of maternal hyperthyroidism (i.e. previous treatment for hyperthyroidism, thyroidectomy for Graves’ Disease or radio-iodine treatment), all infants should be examined at birth for signs of thyrotoxicosis, including resting heart rate. All mothers should be told what signs and symptoms to look for i.e. irritability, excessive feeding, poor weight gain and should receive a parent information leaflet on ‘Symptoms of thyrotoxicosis in my baby.’

• Maternal TRAB negative – no additional tests required for baby

• Maternal TRAB elevated or unknown:-

1. Cord blood for fT4,TSH and TRAB. ABSOLUTELY ESSENTIAL. The endocrine biochemist should be alerted in advance, and told of anticipated delivery time so that he/she can arrange for the result to be available as soon as possible (expect fT4 and TSH result within 24 hours, TRAB not urgent). If cord blood has not been taken please ensure a Datix form is completed.
2. Examine the infant at birth for signs of thyrotoxicosis (see below).
3. Monitor the resting heart rate on the postnatal ward with pre-feed observations.
4. The infant should be monitored (resting heart rate, feeding) in hospital for 2-3 days, even if appears well, unless a normal TRAB result has been obtained from the cord or infant, in which case no further tests are required.
5. If the infant has signs of thyrotoxicosis, or is tachycardic at any time, the infant should be admitted to NNU for closer monitoring i.e. continuous heart rate and saturation monitoring.
6. There is a risk that the infant may be hypothyroid (or euthyroid) secondary to maternal treatment, but develop thyrotoxicosis as the (maternal) propylthiouracil wears off over the first week (see below).

• If the mother has been on antithyroid treatment during pregnancy (carbimazole, propylthiouracil) and this has been stopped several weeks before delivery, than the infant should be managed as above (see section above ‘maternal TRAB elevated or unknown’).
• If the mother is on antithyroid treatment at delivery the infant may have treated hypothyroidism, and develop thyrotoxicosis over the first week of life as antithyroid drug levels fall. The infant should be managed as for elevated or unknown TRAB, and the infant should also be reviewed clinically and have thyroid function tests done at 7 days of age. The infant should be reviewed again at 10 days of age. Further thyroid function tests will be required at 10-14 days, but the timing of these will depend on the results at 7 days, and the infant’s clinical status. If in any doubt repeat thyroid function test at 10 days/discuss with Paula Midgley.

• Breast feeding is not contraindicated in mothers treated with thionamides after delivery.
• Both propylthiouracil and methimazole (to which carbimazole is metabolized) are detected in breast milk but appear not to affect neonatal thyroid function if mothers dose of carbimazole is < 30 mg/day and propylthiouracil dose is < 300mg / day. Doses greater than this should be referred to the pharmacist for advice, preferably before delivery.
• Rare idiosyncratic reactions (eg agranulocytosis) might occur with either drug, and the infant should be watched for signs of infection and liver disease (jaundice, bruising).
• Monitoring of the infant's complete blood count and differential is advisable if there is a suspicion of a drug-induced blood dyscrasia.