The thyroid gland of the fetus starts functioning at about 20 weeks’ gestation to produce thyroxine for general development. About 1 in 3000 babies born in the UK has congenital hypothyroidism (CHT) and lack the hormone thyroxine, which in turn affects their growth and can lead to learning disabilities. However, early detection and treatment with thyroxine allows them to develop normally.

It is important to remember that the routine day 5 test may not identify very preterm babies with this condition. Therefore, all babies born at less than 32 weeks’ gestation are recommended to have a preterm repeat test at 28 days of age or on discharge home, whichever is the sooner, to ensure they are appropriately screened.

Sickle cell disease (SCD) affects haemoglobin and the oxygen-carrying capacity of the red blood cells, hence it is also known as sickle cell anaemia. This is a serious inherited blood disorder in which the normal round flexible disc-like cells change to elongated sickle or crescent-moon shapes when deoxygenated and under stress, forming clusters and blockage, resulting in tissue hypoxia, causing pain and severe anaemia. Babies who have SCD will require specialist care throughout their lives. The incidence in the UK is about 1 in 2000 babies.