The placenta plays a key role in programming Compensation carries a price. In an unfavorable environment, the developing baby makes attempts to compensate for deficiencies. However, the compensatory effort often carries a price Attempts made after birth to reverse the consequences of programming may have their own unwanted consequences. Problems may arise when postnatal conditions prove to be other than those for which the fetus prepares. Fetal cellular mechanisms often differ from adult processes .
Fetuses react differently to sub-optimal conditions than do newborn babies or adults.
The effects of programming may pass across generations by mechanisms that do not involve changes in the genes. Programming has different effects in males and females .