In order to prevent behavioural and emotional problems in children later in life, British researchers have advised expectant mothers to reduce their anxiety and stress levels during gestation.
The researchers from Imperial College London hope that it will raise families' awareness of the importance of reducing levels of stress and anxiety in expectant mothers.
They say that reducing stress during pregnancy could help prevent thousands of children from developing emotional and behavioural problems.
It can also increase the likelihood of later violent or criminal behaviour.
The findings have suggested that the effects of stress during pregnancy can last many years, including into adolescence.
"We all know that if a mother smokes or drinks a lot of alcohol while pregnant it can affect her fetus," said Glover.
"Our work has shown that other more subtle factors, such as her emotional state, can also have long-term effects on her child.
"Our research shows that stress due to the mother's relationship with her partner can be particularly damaging," Glover added.
The researchers say that the stress hormone cortisol may be one way in which the fetus is affected by the mother's anxiety during pregnancy.
Usually the placenta protects the unborn baby from the mother's cortisol, by producing an enzyme that breaks the hormone down.
When the mother is very stressed, this enzyme works less well and lets her cortisol through the placenta.
The researchers suggested higher the level of cortisol in the womb, the lower the toddler's cognitive development or "baby IQ" at 18 months.