Long-Term Course of Hypothyroidism Detected through Neonatal TSH Screening in a Population-Based Cohort of Very Preterm Infants Born at Less than 32 Weeks of Gestation

Newborn screening for primary congenital hypothyroidism: past, present and future

This manuscript reviews the evolution of newborn screening for primary congenital hypothyroidism (CH) and explores future strategies to enhance diagnostic accuracy. Over the past few decades, newborn screening has expanded globally, significantly reducing the incidence of severe forms of the disease. However, challenges persist, especially regarding the overdiagnosis of mild cases of primary CH, which may not require treatment. Omic sciences may help researchers to enhance the understanding of primary CH and to uncover new biomarkers to identify mild cases with altered proteomic and/or metabolic profiles associated with the need for treatment. Record-linkage studies can help deepen knowledge on the long-term outcomes of affected children identified through newborn screening. Nevertheless, despite 50 years of newborn screening for primary CH, a minority of newborns currently benefit from this critically important public health intervention. Efforts should be done to expand access to newborn screening globally, especially for those born in developing countries.

The prevalence of hypothyroxinemia in premature newborns

Congenital hypothyroidism diagnosed by TSH assessment in bloodspot screening may be overlooked in preterm newborns due to immaturity of the hypothalamus-pituitary-thyroid axis in them. The purpose of the study was to determine the prevalence and causes of hypothyroxinemia in preterm newborns, determined by TSH and FT4 serum concentration measurement, performed on the 3-5^th day of life. We assessed TSH, FT4 and FT3 serum concentration on the 3-5^th day of life in preterm children born at our centre within three consecutive years. We assessed the incidence of hypothyroxinemia, and its cause: primary hypothyroidism, secondary hypothyroidism or low FT4 syndrome - with normal TSH concentration, its dependence - among others - on gestational age (GA), birth body weight (BBW) and being SGA. A total of 525 preterm children were examined. FT4 concentration was decreased in 14.9% of preterm newborns. The most frequent cause of hypothyroxinemia was low FT4 syndrome (79.5%). More than 92% cases of hypothyroxinemia occurred in children born before the 32^nd week and/or with BBW below 1500 g. Thus, every fourth child in these groups had a reduced FT4 concentration. Neonates with hypothyroxinemia were significantly lighter than those with normal FT4. In older and heavier neonates with hypothyroxinemia, serious congenital defects were observed. Neither IVH nor SGA nor twin pregnancies predispose children to hypothyroxinemia. Among newborns with untreated hypothyroxinemia in whom TSH and FT4 assessment was repeated within 2-5 weeks, a decreased FT4 concentration was confirmed in 56.1% of cases. As hypothyroxinemia affects 25% of newborns born before the 32^nd week of gestation and those in whom BBW is less than 1500g, it seems that in this group of children the newborn screening should be extended to measure serum TSH and FT4 concentration between the 3-5^th day of life. In older and heavier neonates, additional serum TSH and FT4 assessment should be limited to children with severe congenital abnormalities but not to all SGA or twins. Despite the fact that the most common form of preterm hypothyroxinemia is low FT4 syndrome, it should be emphasized that FT4 remains lowered on subsequent testing in more them 50% of cases.