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Circulating sex hormone-binding globulin and testosterone in newborns and infants
N J Bolton1, J Tapanainen, M Koivisto
1Department of Clinical Chemistry, University of Oulu, Finland.
Insights
Newborns have distinct sex hormone-binding globulin (SHBG) and testosterone (T) levels. The free androgen index (FAI) in infant boys is significantly higher than in girls, despite early T elevations lacking biological significance.
Area of Science:
- Endocrinology
- Neonatal Physiology
- Reproductive Biology
Background:
- Sex hormone-binding globulin (SHBG) and testosterone (T) play crucial roles in development.
- Understanding their dynamics in newborns is essential for assessing hormonal health.
- The free androgen index (FAI) provides insight into biologically active testosterone levels.
Purpose of the Study:
- To measure SHBG and T concentrations in cord blood and infant circulation.
- To calculate the FAI and assess its trends in early life.
- To compare hormonal profiles between male and female infants.
Main Methods:
- Blood samples collected from full-term and pre-term newborns' cord blood.
- Venous blood samples analyzed from 100 full-term infants (1-204 days old).
- Quantification of SHBG and T levels, followed by FAI calculation.
Main Results:
- Boys' cord sera showed higher T concentrations (arterial vs. venous) and FAI than girls'.
- SHBG levels were lower in cord sera than maternal circulation but higher in boys than girls.
- Infant boys exhibited a T peak at 1-3 months, but their FAI remained relatively low, though higher than in infant girls.
Conclusions:
- Neonatal androgen levels differ significantly between sexes, with boys having higher FAI.
- Early elevations in infant male testosterone may have limited biological significance due to SHBG binding.
- The FAI is a critical indicator for assessing biologically active testosterone in neonates and infants.
Abstract:
The concentrations of sex hormone-binding globulin (SHBG) and testosterone (T) were measured in the cord blood of full-term newborns (14 boys, 15 girls) and pre-term newborns (10 boys, 5 girls), and in the venous circulation of 100 full-term infants aged 1-204 days. The ratio of T to SHBG (the 'free androgen index', FAI) was calculated to reflect the level of unbound T (the free, biologically active fraction). In boys' umbilical cord sera, T concentrations were significantly greater in arterial than in venous sera, while there was no such difference in the concentration of SHBG. Levels of SHBG in cord sera were considerably lower than those seen in the maternal circulation at term, but they were significantly greater in boys' than in girls' cord sera. Levels of T, and the FAI, were significantly greater in boys' arterial cord sera than in girls'. In early infancy, SHBG concentrations rose in both sexes, the highest values being seen in girls. In infant girls, levels of T and the FAI were constantly low. In infant boys, the expected peak in serum T concentrations was observed at 1-3 months the values approaching those seen in men. In contrast, values of the FAI at this age were relatively low, similar to those seen in women. This suggests that the elevation of male serum T during the first months of life lacks biological significance. However, it is important to realise that the FAI in male infants is about one order of magnitude larger than that in female infants at this time.