Daily chocolate consumption by pregnant women could have a positive effect on placenta and foetal growth and development by improving blood flow, scientists say.

Research to be presented to the Society for Maternal-Fetal Medicine examined whether high-flavanol chocolate could reduce pre-eclampsia, a late-term disorder that can result in a range of serious health problems for both the mother and the foetus.

Chocolate has been shown to improve risk of pre-eclampsia but results have been conflicting, so the present study set out to examine the role of flavanols.

Flavanols are compounds found in cocoa that are commonly found in dark, bitter chocolate and have been linked to numerous health benefits including reduced blood pressure and improved mental function.

The study recruited 129 women between 11 and 14 weeks' gestation and randomly separated them into two groups given 30 grams per day (about the same as a small bar of chocolate) of either low-flavanol or high-flavanol chocolate for 12 weeks.

Pre-eclampsia, gestational hypertension, placenta weight and birth weight were measured, while measurements of blood flow were taken at the start and after 12 weeks.

No significant difference between the two groups were found on any measure, but both groups showed an improvement in blood flow much greater than expected in the general population.

"This study indicates that chocolate could have a positive impact on placenta and foetal growth and development and that chocolate's effects are not solely and directly due to flavanol content," researcher Emmanuel Bujold said.

The study did not have a control group consuming no chocolate, so further research will be needed to confirm the finding and to test the effect of different quantities of chocolate.