A score of 10 is uncommon, due to the prevalence of transient cyanosis, and does not substantially differ from a score of 9. Transient cyanosis is common, particularly in babies born at high altitude. A study carried out in Peru, that compared babies born near sea level with babies born at very high altitude (4340 m or 14,138 ft), found a significant average difference in the first Apgar score but not the second. Oxygen saturation also was lower at high altitude.