NSW babies are getting heavier

A recent study (1) has shown that newborn babies in NSW are getting heavier, raising questions about the possible long term health effects. Similar trends have been seen in Sweden and Canada.

Babies (single, live and delivered at term) born between 1990 and 2005 were included in the study. Information was obtained from NSW Midwives Data collection reports. Birth size was assessed using mean birth weight, number of babies weighing over 4000g and/or 4500g and number of babies born large for gestational age (LGA). LGA was defined as more than the 90th centile for sex and age using Australian birth centile charts. 

Over the 16 years, birthweight increased by 23g for boys and 25g for girls. There was a 10.5% increase in boys and a 15.2% increase in girls weighing over 4000g at birth and a 17.9% increase in boys and 20% increase in girls weighing over 4500g. Boys born LGA increased by 17.9% and girls by 21%.  During this time, mothers also changed - they smoked less, were older at delivery and more had  gestational diabetes.

The study showed there is a trend of babies being born heavier. Nearly 1 in 6 boys and 1 in 10 girls now weigh more than 4000g at birth. Having a baby born LGA was most strongly associated with the mother having gestational diabetes, having had more than one child, being older ( >35 years) and from Polynesia. Ethnicity is an important factor in birth weight and growth. Other factors included not smoking, pre-exising diabetes and hypertension. 

The  adverse health effects of having bigger babies include an increased risk of overweight/obesity,cancer, asthma, and type1 diabetes in later life. For the mother during delivery, there is an increased risk of injury to both herself and baby and possibly the need for a caesarian section.

Reference:

Hadfield RM, Lain SJ et al. Are babies getting bigger? An analysis of birthweight trends in New South Wales 1990-2005. MJA 2009;190(6):312-315