Why we're having bigger babies (and what it means for you)

There’s a ‘big baby’ boom in Australia as diet and lifestyle factors seem to be leading to bigger newborns. Here’s what you need to know about having a larger baby.

If you’re having a heavy baby, what does this mean for your health, during and after pregnancy and labour? 
Dr Ronald McCoy, spokesperson for the Royal Australian College of General Practitioners, explains why we seem to be  having bigger babies and what you need to know if you’re expecting a larger baby. 
The average newborn baby’s weight is around 3.4kg however over the past decades this average seems to have increased. Researchers have found the proportion of babies born larger than average increased by 18 per cent for boys and 21 per cent for girls between 1990 and 2005. 
If your baby weighs more than 4kg at birth, your GP or midwife may say they have macrosomia, which means ‘large body’. Almost 1 in 6 boys and 1 in 10 girls now weighs more than 4kg at birth, due to a number of factors. 
As the age of women having babies has increased (the average maternal age was 29.9 years in 2008, compared to 29 years in 1999), this is thought to have an effect on newborn weight. According to a report by the Australian Institute of Health and Welfare, larger birth weights are believed to be linked to a rise in maternal age and an increased number of gestational diabetes cases. The decreased number of women smoking during pregnancy is also believed to be a contributing factor. 

Your pregnancy

During your pregnancy, you will usually have regular check-ups, which include measuring your baby's growth. These measurements can give you and your midwife or GP an indication if how big your baby is, however there can be a difference of up to 15 per cent between your baby’s predicted weight and its actual birth weight. 
If your scans indicate that your baby is larger than expected, your blood sugar levels may be monitored. High blood sugar levels can be an indication of gestational diabetes.

Why is my baby heavy?

You may be more prone to have a large baby if you have gestational diabetes or pre-existing diabetes. Research has found that there is a link between gestational diabetes, being overweight or obese during your pregnancy, and heavier babies. Having a high body mass index (BMI) or excess weight gain during pregnancy can also influence your baby’s weight. Going over your due date may also affect your baby's birth weight.
Chubby baby holding mother's hand

The birth

Giving birth to a larger baby can have an effect on the type of labour and birth you have. 

  • Almost two thirds of very big babies (4.5kg or more) are born vaginally, but this may be difficult for the mother and child 
  • Labour may take longer
  • There may be an increased risk of heavy blood loss
  • Possible risk of perineal tear
  • 1 in 13 babies born heavier than 4.5kg are likely to experience shoulder dystocia during birth. This occurs when your baby's shoulder becomes stuck in the birth canal. The medical team may need to intervene to help free its shoulders
  • A larger baby may mean you need an induction or Caesarean

Will a heavy baby have health problems?

Research at the University of Exeter Medical School recently found that, “Being born very large or very small can carry health risks for a newborn baby, particularly when that’s at the extreme end of the spectrum. Higher and lower birth weights are also associated with conditions such as type 2 diabetes later on in life".

If your midwife or GP think you are having a heavier than normal baby and you and/or they are concerned about the birth, it's important to discuss the options and any fears you have.
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