Sad mothers-to-be are at greater risk of having small babies that may die soon after birth, a study found.
Being depressed or anxious while pregnant doubled the chances of a woman having a low birth-weight baby, the research showed.
Scientists made the discovery after assessing the mental state of 583 women in the last three months of pregnancy from two rural areas of Bangladesh.
They found that 18pc of the mothers were experiencing depressive symptoms and 26pc suffered from general anxiety.
A total of 19pc of the women went on to have small babies weighing less than 2,500 grams.
Analysis showed that depressed and anxious women were twice as likely to give birth to small babies than those who were mentally healthier.
"These women were much more likely to give birth to very small babies," said lead researcher Dr Hashima-E-Nasreen, from the Bangladesh Rural Advancement Committee in Dhaka, who worked with colleagues from the Karolinska Institute in Sweden.
"This is a worrying problem, since low birth weight is strongly associated with infant death."
The findings were reported in the journal BMC Public Health.
In their paper, the scientists concluded: "The reduction of LBW (low birth weight) at term is an important indicator of the internationally agreed Millennium Development Goals for reducing child mortality and is a key indicator of progress.
"Our study indicates that, in order to achieve this goal, maternal depressive and anxiety symptoms during pregnancy need to be addressed."