Quantitative ultrasound (QUS) measurement of tibial speed of sound (SOS) can be used to determine bone strength. Children conceived with assisted reproduction treatments (ART) are taller than naturally conceived (NC) children, so we hypothesized that these infants would have higher SOS levels than NC infants. Thirty-seven ART (ART group) and 51 NC neonates (NC group) were included in the study. Tibial initial SOS (iSOS) was measured within 96 hours of birth using QUS. Measurements were performed weekly until the infant was discharged from the hospital. The iSOS levels of the ART group (2823.41 +/- 110.8 m/sec) were lower than those of the NC group (2917.14 +/- 145.6 m/sec) (p=0.001). A decrease in SOS levels was observed in 39 of 53 infants who had serial scans. The difference in SOS levels between the first and last scan was significant (p<0.02). In vitro manipulation during the periconceptual period can result in metabolic alterations in bone mineral content. Contrary to our null hypothesis, bone SOS of infants in the ART group was found to be lower than in the NC group. Moreover, bone SOS decreases in early postnatal life. This result emphasizes the fact that even with advances in nutritional care, the ex utero environment remains a poor substitute for in utero development.