Experimental removal of fetal adrenal glands in sheep reduces mitochondrial content and oxidative phosphorylation capacity in skeletal muscle at term, while cortisol infusion before term prematurely increases these parameters, indicating a direct association between glucocorticoid exposure and fetal mitochondrial development.

When the fetus is exposed to rising levels of cortisol, it triggers the production of more energy-making structures inside muscle cells, called mitochondria, and makes them better at producing energy. This happens because cortisol directly activates genes inside the mitochondria and also boosts another hormone that does the same thing. Without enough cortisol, these energy factories don't develop properly, and the muscle cannot make enough energy for life after birth.