The growing number of extremely obese pregnant woman in New Zealand is a "scary problem'' as new research shows they face a greater risk of complications during pregnancy, an expert says.
The latest findings of the Australasian Maternity Outcomes Surveillance System have found women with extreme morbid obesity are more than twice as likely to need a caesarean section.
They also have higher rates of complications such as gestational hypertension, gestational diabetes and pre-eclampsia.
The study looked at 370 women in Australia who weighed more than 140kg or had a body mass index of greater than 50 _ twice the healthy norm of 20-25.
It found 38 per cent of those women had to have labour induced and 52 per cent needed a caesarean section, compared with 21 per cent and 32 per cent respectively for the general population.
Lead investigator Professor Elizabeth Sullivan, of the University of New South Wales, said she would expect to see similar rates of complications in New Zealand women.
In 2010, there were 749 pregnant women in New Zealand and Australia classed as extremely morbidly obese.
Auckland University Professor Lesley McCowan, an expert in maternal fetal medicine, said national data was only just starting to be collected in New Zealand.
Anecdotally, however, the problem of extremely obese mothers was growing.
"Unfortunately, it looks as if that group with extreme obesity is becoming a bit more common than it used to be,'' she told APNZ.
"It's a scary problem and it's one we've really got to start trying to address early in childhood to reverse the cycle.''
Dr McCowan said very obese women had increased risks of "virtually every pregnancy complication that you can think of''.
"There's a direct correlation between many pregnancy complications and the degree of obesity. So for example, your chance of having a stillborn baby or developing hypertensive problems or gestational diabetes - those risks increase as the maternal body mass index gets higher.''
The risks were higher not only for mothers with extreme obesity, but also those with body mass indices greater than 30.
Dr McCowan said very obese women also faced labour difficulties and were more likely to have big babies, which led to the higher rate of caesarean sections.
"It's not a straightforward delivery for them or for the doctor performing the operation, just because of the technical aspects.
"It's an increasing challenge, so operating theatres are now equipped with beds that can cope with bigger mothers and we've got different types of equipment to be able to deal with these bigger mothers when they're having their babies.''
There were also physical challenges for the staff who provided care during labour and delivery, she said.
Dr McCowan said there was a strong correlation between obesity and social deprivation.
"It's also more of a problem particularly amongst our Pacific mothers, who have higher rates of obesity in their population, and also more common amongst Maori mothers than Europeans.''
Dr McCowan said it was important that appropriate monitoring of obese pregnant women was put in place.
"One of the things we can do is to educate and help mothers to reduce their weight gain during pregnancy, and that appears to reduce the risk of a number of pregnancy complications.''
Australian researcher Dr Sullivan said she was surprised the women in the study had done "remarkably well'' despite the higher rates of complications.
There were no deaths among the women in the survey although 2 per cent were admitted to intensive care - about one in 50.
She said mothers had an increased risk of wound infections after birth, while their babies had higher rates of adverse outcomes.