High Altitude Impact on Fetal Growth

Observing growth of embryo chicks in the egg at sea level and altitude shows us that the level of oxygen available to chick embryos as well as their ancestry combine to determine the chicks’ size at birth.

Low oxygen availability at  altitude for the chick embryo impairs  the chick’s growth -  but the mother hen’s life history also plays a part in determining her chick’s size.

In contrast to  studies in mammals, hypoxia effects on chick embryo growth can be assessed directly by studying the fertilized egg without accounting  for changes in the mother or  placenta - See chapter 3 .

When eggs of sea level hens  are  incubated at sea level, chicks are much  larger at birth than  when  the same eggs are  incubated at  high altitude. The difference  shows  that low oxygen at altitude  (represented by the height of the oxygen level column - O) suppresses chick growth.  When  eggs  laid by high  altitude hens are incubated at sea level the chick is larger at birth than when that egg is incubated at altitude – again showing that low oxygen  at  high altitude suppresses chick growth. 

We can make another important and interesting observation. When both sea level  hens’ eggs and high altitude  hens’ eggs are incubated at  the same oxygen  level  at sea level, the chick from   the  high  altitude hen is larger. The same occurs when both sea level  and high altitude  hens’ eggs are incubated at  the same oxygen  level  at high altitude,  the chick from   the  high  altitude hen is again larger than the sea level chick. Clearly many generations of  life at high altitude has made the high  altitudes hens’ eggs grow better at the same oxygen level. See Chapter 12 for similarities in human birth wight at altitude. Picture kindly  provided by Dino Giussani.  Itani N, et al. The highs and lows of programmed cardiovascular disease by developmental hypoxia: studies in the chicken embryo. J Physiol . 2018;596(15):2991. Available from: http://www.ncbi.nlm.nih.gov/pubmed/28983923

For more information of models of growth restriction see chapter 12 in Life Before Birth.