Fertility and pregnancy * Babies and children

The risks of having a big baby

Chun Chun weighs 15.5 pounds Macrosomia can be unexpected

The birth of another super-sized baby - a 15.5 lb boy born in China - casts the spotlight on a relatively common event - large newborns.

The event, also known as macrosomia, takes place in between one and 10 per cent of deliveries, though the size of boy born this week is an anomaly.

But it does happen, and often times parents are caught unaware.

When Karen Gallacher was expecting last year, she was warned that her baby might be large and weigh up to 9 lb. But when Farrah was born, she weighed 12.6 lb, a UK record.

The weight of the average newborn in the UK is around 7.5 lb for boys, and 7.25 lb for girls.

Ms Gallacher is a petite 5ft 2in, and had a normal pregnancy, without particular food cravings.

In other words, while macrosomia can be tentatively diagnosed during pregnancy, it is only confirmed once the baby has been born and weighed.

The factors that are associated with fetal macrosomia can include:

  • Genetics: parental weight and height may play a role in determining newborn birth weight - though this is not always the case.

  • Duration of gestation.

  • Gestational diabetes, a type first diagnosed during pregnancy or having diabetes

Gestational diabetes is a known risk factor for large babies, as well as a number of complications for mother and baby. If a woman has higher than normal levels of glucose in her blood, the excess glucose is passed to the baby via the placenta, causing the baby to make insulin, resulting in growth.

A large baby is more at risk of injury and may need to be delivered by Caesarean section.

Larger-than-average babies born to women with diabetes are also at higher risk of low blood sugar levels, jaundice or breathing problems and are also more at risk of having diabetes themselves later in life.

Ethnicity may also influence birth weight. For instance, Hispanic women in the United States have a higher risk of fetal macrosomia compared to white, African-American and Asian women, even when controlled for diabetes.

Despite the known risk factors, no combination of these can be used to accurately predict macrosomia.

This article was published on Wed 8 February 2012

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