Normally during pregnancy, the placenta protects the fetus from the stress hormone cortisol. But when the mother becomes stressed, the placenta’s protection can be compromised and the cortisol may have lasting effect on the fetus.
Researchers at the Imperial College in London looked at how a mother’s stress and anxiety during pregnancy alters brain development in a fetus and later life. They were able to conclude that there was a greater risk of developing a range of problems. These include emotional problems such as anxiety or depression, behavioral problems such as ADHD, and learning disabilities. Other studies have implied that later violent or criminal behavior can be linked to this prenatal stress.
Another study from the University of Miami supports this research - babies of mothers who were stressed during pregnancy demonstrated higher rates of depression, anxiety and were smaller than average.
Similar to English research psychobiologist Miguel Diego and colleagues found that the stress hormone cortisol is the mechanis by which a mother's stress is transmitted to her unborn baby.
Dr. Diego further explained that cortisol can affect the mother's vascular function, thereby reducing blood flow to the fetus, which could affect fetal growth by diminishing the amount of oxygen and nutrients that are delivered.
The researchers made the point though that the effect of stress on a fetus was relevant only to women who were under extreme amounts of anxiety or feeling depressed. Dr. Diego recommended that any mothers who feel that they might be at risk should contact the physician and discuss how to manage the mental state during the course of the pregnancy.