UPBEAT: how to tell which babies are too large for their gestational age?

Dr Dharmintra Pasupathy, Professor Lucilla Poston, Dr Matias Vieira, SCOPE collaborators, UPBEAT collaborators

Researchers have studied over 1,000 women who took part in the UPBEAT trial to try and find out more about babies that are heavier than normal.

In developed countries, more and more babies are being born heavier – the number of babies with a high birth weight has increased by 25% over the last 20 years. However, a high birthweight can mean problems for the baby. These include injury at birth, a higher chance of childhood obesity, and at worst, can result in death.

To stop this from happening, we need to understand when a heavy baby is too heavy.

When a baby is unusually large for its age in the womb, it is called large for gestational age or LGA. At the moment, deciding when a baby is too large doesn’t take into account factors that can affect how the baby grows. These are things like a mother’s ethnicity, height and weight, and the sex of the baby. Significantly, these could be used to tell when a large baby might cause complications. In an earlier study funded by Tommy’s, we managed to accurately say which factors were related to health problems, and tell which babies were affected.

Women who are obese before pregnancy are more likely to have babies that are LGA, so it makes sense to focus on this group to study large babies. Researchers supported by Tommy’s looked at over 1,200 obese women who took part in the UPBEAT study to find out why some babies grow too much, and when this can be harmful.

Around 10% of the babies in the study were LGA. The results suggest that the reasons for babies growing too much aren’t the same in women who get diabetes during pregnancy, and those who don’t. Even before 20 weeks of pregnancy, there were differences in LGA babies depending on if their mothers had diabetes.

In women who don’t have diabetes, it appears that the size of the baby might be to do with its parents’ genetic makeup. These women tended to be lighter early in pregnancy, but put on more weight later on. Women who later got diabetes showed signs of unusual chemical reactions in the body from as early as 15 weeks.  

The results of this study are vital to understand why some babies grow more than others. The fact that the reasons for LGA babies are different in women with and without diabetes will help us to pick out early on babies that are at risk. 

In future studies, we would like to find out if we can see the same patterns in non-obese women.

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This study takes place in a Tommy's centre and is funded by Tommy's, the National Institute for Health Research and the CAPES program (Brazil)

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