Differential Effect of Sex in Newborn Vertebrae and Risk of Osteoporosis

Presentation Number: LB-OR01-2
Date of Presentation: March 5th, 2015

Skorn Ponrartana*1, Patricia C Aggabao1, Naga L Dharmavaram1, Carissa L Fisher1, Philippe Friedlich1, Sherin U Devaskar2 and Vicente Gilsanz1
1Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, CA, 2Mattel Children's Hospital, UCLA, Los Angeles, CA


Background: The cross-sectional area (CSA) of the vertebra is smaller in females than in males throughout childhood, adolescence, and at the timing of peak bone mass – a major determinant of osteoporosis and future fracture risk. We examined whether these sex-related differences in the development of the axial skeleton are also present at birth.

Methods: Vertebral CSA, vertebral height, and intervertebral disc height were measured from the sixth thoracic to the fifth lumbar vertebrae using magnetic resonance imaging (MRI) in 70 healthy full-term newborns (35 male and 35 female). Additionally, measures of the length and CSA of the humerus, musculature, and adiposity were obtained.

Results: Weight, body length, head and waist circumferences, and MRI measures of musculature and adiposity did not significantly differ between sexes (all P’s ≥ 0.060). Compared to newborn boys, girls had significantly smaller vertebral cross-sectional dimensions (1.465 ± 0.11 vs. 1.309 ± 0.12; P < 0.0001) – a disparity that was independent of gestational age, birth weight, and body length. In contrast, sexes were monomorphic with regard to vertebral height, intervertebral disc height, and spinal length (all P’s ≥ 0.108). There were also no sex differences in the length or cross-sectional dimensions of the humerus (both P’s ≥ 0.151).

Conclusions: Factors related to sex influence fetal programming of the axial skeleton. The smaller vertebral CSA in females is associated with greater flexibility of the spine that could represent the human adaptation to fetal load. Unfortunately, it also imparts a mechanical disadvantage that increases stress within the vertebrae for all physical activities and the susceptibility for fragility fractures later in life.


Nothing to Disclose: SP, PCA, NLD, CLF, PF, SUD, VG