Sexual Dimorphism in Newborn Vertebrae and Its Potential Implications

Area of Science:

• Developmental biology
• Pediatric orthopedics
• Skeletal biology

Background:

• Sex-related differences in vertebral cross-sectional area (CSA) are known in children and at peak bone mass.
• These differences are significant determinants of osteoporosis and future fracture risk.

Purpose of the Study:

• To investigate if sex-related differences in vertebral CSA are present at birth.
• To understand early developmental influences on the axial skeleton.

Main Methods:

• Magnetic resonance imaging (MRI) was used to measure vertebral CSA, height, and intervertebral disc height in 70 healthy newborns (35 males, 35 females).
• Humerus length and CSA, musculature, and adiposity were also assessed.

Main Results:

• Newborn girls exhibited significantly smaller mean vertebral CSA compared to boys (1.31 ± 0.12 vs 1.47 ± 0.11, P < .0001).
• Sex was identified as an independent predictor of vertebral CSA, regardless of gestational age, birth weight, or body length.
• No significant sex differences were observed in vertebral height, disc height, spinal length, humerus dimensions, musculature, or adiposity.

Conclusions:

• Sex-related factors influence the fetal development of the axial skeleton.
• Smaller vertebral CSA in females may enhance spinal flexibility for fetal positioning but could predispose to increased vertebral stress and fragility fractures later in life.