In a 2009 study, researchers at Harvard's MassGeneral Hospital for Children as well as other institutions analyzed the blood
oxygen levels of newborns when they were placed in cribs versus car seats and found that nearly one - quarter of the time that the babies were in car seats, their
oxygen saturation levels (the ratio of
oxygen - saturated hemoglobin to total hemoglobin in their blood) dropped below 95 percent, the cutoff for what is considered
normal.