A recent study by Kaiser Permanente Division of Research, which was published in the journal Human Reproduction indicates that depressed women were twice likely to deliver their babies before the term or less than 37 completed weeks of gestation.

The research was conducted on 791 women. More severe the depression, greater the chances of preterm delivery.

Preterm birth is caused due change hormone levels.“What we do know is that a healthy pregnancy requires a healthy placenta, and that placental function is influenced by hormones, which are in turn influenced by the brain,” Dr. De-Kun Li, lead author of the study said.

According to Diana Dell, assistant professor of psychiatry and obstetrics-gynecology at Duke University Medical Center, depression may be the cause of baby being under weight at the time of birth. It can also cause elevated levels of cortisol (a stress hormone) and changes in attention or alterations in electroencephalography (an infant brain test).

Research also shows that certain antidepressants may be risky to the baby but some of the anti depressants given to the mother are safer than others. The expectant mother is unable to take care of herself and the fetus because of depression. An untreated depressed or anxious pregnant woman, says Dell, "generates some pretty noxious chemicals" that are not good for a fetus.