Fetal lipid metabolism.

The fetus grows at a rate unparalleled by that during any other stage of life. To maintain its rapid growth rate, the fetus requires a significant amount of cholesterol and fatty acids. For structural purposes alone, the fetus requires 1.5 mg of cholesterol per gram of tissue, not including the brain. Cholesterol is also required as a precursor for various steroidogenic hormones that are critical to normal development, such as estrogen, and for metabolic regulators, such as oxysterols. More recently, it was found that cholesterol is necessary for the activation of Sonic hedgehog (Shh) (1), an organizer involved in early spatial patterning of the forebrain (2). Fatty acids are needed as structural components of tissues, as a source of energy, and if metabolic regulation in the fetus is similar to that in the adult, as activators of transcription factors. The fetus, as in any tissue, acquires its cholesterol and fatty acids from two different sources, endogenous and exogenous.