Scientists at the University of Helsinki asked 300 women to record their chocolate consumption and stress levels during pregnancy. Those that treated themselves regularly reported more smiling and laughter in their babies when questioned six months after birth, they write in the Feburary issue of Early Human Development (vol 76, issue 2, pp 139-145).
The scientists also found that stressed women who ate chocolate were more likely to say their babies were less fearful in new situations.
"Maternal prenatal stress predicted more negatively tuned ratings of the infant temperament, particularly among those who reported never/seldom chocolate consumption. However, this effect was not observed among the mothers reporting weekly or daily chocolate consumption," noted Katri Raikkanen and her colleagues.
While they propose that chemicals in chocolate previously shown to alter mood could be passed on to the baby in the womb however they could not rule out the impact of other potential factors on the babies' behaviour.
Chocolate manufacturer Cadbury's told the BBC Online that the chemical in chocolate thought to boost mood, phenylethylamine, is found in much smaller quantities in chocolate compared to other foods like tomatoes and fruit.
"We think the mood altering effects of chocolate are more to do with psychology rather than chemicals. When chocolate melts in the mouth, it has a soothing, pleasurable quality and people feel happy about it."