Experts say there should be a greater focus on encouraging overweight women to lose weight before they get pregnant.

Researchers have analysed data for 42,582 first-time mothers with singleton pregnancies who gave birth at the Royal Prince Alfred Hospital in Sydney between January 1990 and December 2014.

They found that the prevalence of overweight among first-time pregnant women increased from 12.7 per cent in 1990–1994 to 16.4 per cent in 2010–2014; the prevalence of obesity rose from 4.8 per cent to 7.3 per cent over the same period, while the proportion of women with a normal range body mass index (BMI) fell from 73.5 per cent to 68.2 per cent.

The researchers estimated population attributable fractions (PAFs) - the proportional reduction in population disease that could be achieved were exposure to overweight and obesity reduced to a more desirable level.

They found that the PAFs for adverse maternal and neonatal outcomes increased across the study period; during 2010–2014, 23.8 per cent of pre-eclampsia, 23.4 per cent of foetal macrosomia, and 17 per cent of gestational diabetes were attributable to overweight and obesity.

The authors write that if overweight and obese women were to have moved down one BMI category during 2010–2014, 19 per cent of preeclampsia,15.9 per cent of macrosomia, 14.2 per cent of gestational diabetes, 8.5 per cent of caesarean deliveries, 7.1 per cent of low for gestational age birthweight, 6.8 per cent of post partum haemorrhage, 6.5 per cent of admissions to special care nursery, 5.8 per cent of prematurity, and 3.8 per cent of foetal abnormality could have been averted.

“Expert national and international consensus statements support improving pre-conception health and detailed prevention strategies,” the report says.

“They recommend reducing obesity as a means for improving reproductive health outcomes, and potentially also reducing societal costs. The National Health Summit on Obesity called for federal support for life course strategies that incorporate pre-conception care.

“We found that a substantial proportion of the burden of adverse perinatal outcomes for Australian women is linked to maternal overweight and obesity, and that this proportion has steadily increased over the past 25 years.

“Importantly for practice and policy, our results indicate that the frequency of adverse perinatal outcomes could be reduced by shifting the distribution of overweight and obesity among first-time mothers by a single BMI class.

“Investing in obesity prevention strategies that target women prior to their becoming pregnant is likely to provide the greatest benefit,” they concluded.

The study is accessible here.