Mothers-to-be with lower levels of the vitamin folate in their body during early pregnancy are more likely to have babies with lower, or less healthy, birth weights, a study has revealed.
Conversely, researchers from the University of Newcastle upon Tyne, UK, who examined nearly 1,000 women and their newborn babies, found that higher levels of folate (found in some vegetables, fruits and cereals, and also known as vitamin B9, or folic acid) were linked with increased birth weights.
Expectant mothers who smoked were more likely to have lower levels of folate in their blood, which might explain why women who smoke often have lighter babies.
The health benefits of folic acid for babies are already known but this is the first time that folate levels commonly seen in UK mothers in early pregnancy have been linked with birth weight. The study is published in the British Journal of Nutrition.
Seven per cent of all babies born are low birth weight (less than 2.4kg or 5.5lbs) and they have a 50 per cent chance of having a severely disabling condition as a result of being too light. Healthy birth weights are a marker for good health in infancy and later life.
Researchers say that current NHS policy is to advise women to take folic acid at their first pregnancy check-up but this means that many mothers-to-be miss out on taking the vitamin in the crucial, early stages of gestation.
They also say the findings have implications for health promotion policies, adding weight to arguments in favour of fortifying everyday foods like bread and cereals with folic acid.
For the study, Dr Caroline Relton, of Newcastle University's School of Clinical Medical Sciences, and colleagues studied 998 expectant mothers attending a hospital in North West England (West Cumberland Hospital, Whitehaven, Cumbria) and their newborn babies.
The team analysed blood samples that the women gave during their routine antenatal visits (averaging 11.5 weeks gestation) and recorded the amount of folate in their red blood cells - these cells show activity over the previous three months. They gathered lifestyle information, such as smoking habits, from a questionnaire, and also recorded the weight of each baby when born.
Medical evidence suggests that folic acid influences birth weight because it is an essential nutrient for growth and gene expression in the foetus. Smoking is likely to reduce a women's folate levels because it is a significant source of oxidative stress and may alter the ability of the cell to metabolise and ultimately store the vitamin.