The babies of women who are overweight or obese during pregnancy have an increased risk of dying, with babies born to severely obese mothers facing the biggest risk, a new study has found.

According to Swedish researchers, overweight and obesity are common among women of childbearing age and previous studies have suggested a link between a mother's obesity and an increased risk of infant mortality. However to date, findings have been inconsistent.

They decided to look into this further. They analysed the birth records of more than 1.8 million births that were recorded in Sweden between 1992 and 2010. During this time, almost 5,500 infant deaths occurred, two-thirds of which occurred in the neonatal period - the first 28 days of life.

The study found that infant mortality rates increased in line with the mothers' increasing body mass index (BMI) during early pregnancy. In other words, the bigger a mother was in early pregnancy, the greater the risk to her infant.

Among overweight and mildly obese mothers, the risk of infant mortality increased modestly, however among more obese mothers, the risk of infant mortality was more than double.

The researchers noted that in most cases, the child had been born at full term and had died in the neonatal period. Only severe obesity was also linked to deaths in very premature and moderately premature babies.

Causes of death among the infants who had died included sudden infant death syndrome (SIDS), congenital abnormalities, infections and birth asphyxia.

The infants of overweight and obese mothers were found to have an increased risk of death due to birth asphyxia and other neonatal conditions, when compared with the infants of normal weight mothers. Meanwhile, the infants of very obese mothers were found to have an increased risk of death due to SIDS and congenital abnormalities.

The researchers estimated that 11% of infant deaths in the study were due to mothers being overweight or obese during pregnancy.

While they acknowledged that further studies are needed to confirm this link, they insisted that public health officials must now ‘act against the obesity epidemic to promote infant health'.

Details of these findings are published in the British Medical Journal.

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