Babies born to fatter mothers are not only fatter themselves, which we already knew, but also have more fat in their livers, which we didn’t know, according to a new study published in the September 2011 issue of the journal Pediatric Research. The researchers, from Imperial College London, also found that the babies were not only fatter, but had more fat around the abdomen, and this, together with the amount of fat in the liver, increased across the whole range of their mothers’ pre-pregnancy BMI.

Study leader Neena Modi, a professor from the Department of Medicine at Imperial College London and a Consultant Neonatologist at Chelsea and Westminster Hospital, told the press that:

“This study demonstrates that a woman’s BMI, even in the normal range, affects the amount of fat in her baby at birth. Fatter women have fatter babies and there is more fat in the babies’ livers.”

“If these effects persist through childhood and beyond, they could put the child at risk of lifelong metabolic health problems,” she added.

The link between overweight and obese mothers having fatter babies who carry a higher risk of health problems, such as obesity and type 2 diabetes, in later life is already well established, but we don’t know very much about the underlying biology, Modi and colleagues write in their background information.

And so, to test the idea that this could be due to events taking place before birth in the uterus, they studied the body composition of 105 newborn babies at Chelsea and Westminster Hospital and checked it against the BMI of their mothers before they got pregnant.

They used proton magnetic resonance imaging and spectroscopy to scan the babies while they slept. From the scans they measured the total body fat (adipose tissue), where it was distributed, and the fat in the liver cells (intrahepatocellular lipid content).

In adults, high levels of fat in liver and body fat correlate strongly with impaired control of blood sugar.

The results showed that:

  • The pre-pregnancy BMI of the mothers ranged from 16.7 to 36.0.

  • After adjusting for the babies’ weight and sex, there was an increase in their total, abdominal and non-abdominal fat for each unit of increase in their mothers’ BMI.

  • And, for each unit of increase in the mothers’ BMI, there was an increase of 8.6% of fat in the babies’ liver cells , after adjusting for babies’ sex and postnatal age.

  • These increases in abdominal fat and liver fat were also seen across the normal range of maternal BMI.

The researchers concluded that these effects may put babies on a lifelong path that damages their metabolic health.

Modi said:

“There is growing evidence that a baby’s development before birth has a major impact on their health in later life. This means that the prevention of obesity needs to begin in the womb.”

About half of the women of childbearing age in the UK are either overweight or obese, said Modi. But it is also important to note that the link between the amount of fat in the baby and the mother’s BMI is spread across the whole range of BMI, “meaning it’s not just an issue for overweight and obese mums,” she stressed.

“We need to identify what the optimal BMI for the mother is so we can help women ensure that their bodies are in the best possible condition before they get pregnant,” suggested Modi.

BMI, or Body Mass Index, is the person’s weight in kilos divided by the square of their height in metres. According to the World Health Organization system, a BMI of 18.5 to 25 is normal, 25 to 30 is overweight, and over 30 is obese.

In this study, 5 of the mothers had a BMI in the underweight range, 69 were in the normal range, 23 were overweight, and 8 were obese.

Funds from the Medical Research Council and Chelsea and Westminster Hospital NHS Foundation Trust paid for the research.

Written by Catharine Paddock PhD