Transient Postnatal Gonadal Activation and Growth Velocity in Infancy

Abstract

BACKGROUND AND OBJECTIVE: Transient activation of the hypothalamic-pituitary-gonadal axis with a sex steroid surge is observed in boys and girls during the first months of life. However, the role of sex steroids in the regulation of growth has not been substantiated in infancy. We tested the hypothesis that testosterone (T) surge, known to be higher in infant boys than in girls during the transient postnatal gonadal activation regulates linear growth in infants.

Is early postnatal growth velocity, a proxy of minipubertal androgen action, related to adult second‐to‐fourth digit (2D:4D) ratios in men? A test in Cebu, Philippines

“…Importantly, weight velocities during the subsequent 8 months of infancy, wherein T levels are no longer elevated, were not related to digit ratios. Given previous evidence for a relationship between early postnatal growth and T levels (both peaking in the first few months of life; Kiviranta et al, 2016;Kuzawa et al, 2010), this suggests, at least in this sample, that lefthand 2D:4D ratios might serve as a proxy for minipubertal androgen action.…”

“…Testosterone production during minipuberty has important effects on sex-typical patterns of development both in terms of somatic growth and neurobehavioral differentiation. In a sample of infants from Finland, boys showed greater linear growth velocities through their first 6 months of life than girls with the greatest difference observed at 1 month of age -the time of peak testosterone production (Kiviranta et al, 2016). Specifically, urinary testosterone levels were positively and significantly associated with linear growth velocities in both sexes through their first five months of life, with the strongest association observed in the second month (Kiviranta et al, 2016).…”

“…In a sample of infants from Finland, boys showed greater linear growth velocities through their first 6 months of life than girls with the greatest difference observed at 1 month of age -the time of peak testosterone production (Kiviranta et al, 2016). Specifically, urinary testosterone levels were positively and significantly associated with linear growth velocities in both sexes through their first five months of life, with the strongest association observed in the second month (Kiviranta et al, 2016). In a separate sample of boys in the Philippines, greater weight velocity from birth to six months of age, but not at later ages, predicted earlier age at puberty, higher adult testosterone levels, stature, muscularity, and grip strength (Kuzawa et al, 2010).…”

“…To examine the possible relationship between postnatal androgen action and adult 2D:4D ratios, here we relate 2D:4D ratios measured in young (25-26 years old) adult males from Cebu, The Philippines, to weight growth velocities measured during the first year of postnatal life, a proxy of androgen action during this period. Because recent work shows that postnatal T peaks between 1 and 4 months (Kiviranta et al, 2016), we predicted that a higher weight velocity from birth to 4 months of age would predict a more masculine digit ratio, while weight velocities after this period -when T is already low or absent-would be unrelated to adult 2D:4D. This hypothesis builds on our previous report from this population that weight velocity at the age of the minipuberty predicts a wide range of adult testosterone-dependent somatic, hormonal and behavioral traits, consistent with organizational effects of T production at this age (Kuzawa et al 2010).…”

Mini-Puberty and Growth

“…Recent evidence suggests that the androgen exposure of mini-puberty also predicts later sex-typed behavior. 4,5 In this issue of Pediatrics, Kiviranti et al 6 describe yet another effect of this neonatal androgen surge: increased skeletal growth. Although sex differences in linear growth in the first year of life have been described previously, this study is the first to link closely the testosterone surge of mini-puberty with the increased growth velocity in boys relative to girls.…”