Babies that are too small or large near their due date have a greater risk of stillbirth, dying within the first year of life and during hospital admission as they grow older compared with average-weight babies.

Their mothers are also at increased risk of metabolic and cardiovascular disease, with pregnancy outcomes now recognised as an early hallmark of women at risk.

However, there is no agreement on how we define what is a small or large baby, or whether current definitions can accurately predict a baby’s risk of dying, abnormal development or disease.

Currently, babies whose birthweight is in the lowest 10% and highest 10% of a reference chart of birthweights are defined as being too small and too large, respectively. Antenatal care identifies these babies and induction of labour may be advised to prevent death or other risks.

But a study of nearly 1 million pregnancies has shown that the risk of death and poor health at birth is best identified by defining small as the lowest 25% and large as the highest 15% of birthweights at each stage of pregnancy.

Dr Matina Iliodromiti, Reader in Women’s Health and Reproductive Medicine at Queen Mary University of London, and her team want to check the accuracy of their findings in a separate study before suggesting changes to antenatal care for pregnant women and their babies.

The team has also previously shown that mothers of small babies have a greater risk of heart attacks and stroke later in life, and mothers of large babies are at increased risk of diabetes.

So now, they also want to answer the question of whether using these new birthweight thresholds could help to identify which mothers could be at risk of disease better.

To do this, Dr Iliodromiti and her team will analyse data from Scotland for more than a million children over 20 years on events that happened during and after pregnancy, early childhood, their progress at school and possible hospital admissions, as well as childbirth and follow-up data for their mothers.

They are planning to assess how childbirth events and birthweight are associated with developmental milestones and the risk of disease for the children and the mothers.

This information could then be used to guide future care, enabling doctors and midwives to help women and babies at risk to ensure the best possible outcomes.