A new study involving Australian researchers has linked caesareans with a range of long-term risks, including miscarriage.

Women who have caesareans appear to have an increased risk of future miscarriages, stillbirths and placenta problems, scientists say.

University of Western Australia researchers helped their Scots colleagues analyse data from 80 different studies involving almost 30 million women to try to establish the long-term risks and benefits of caesareans compared to natural births.

And it's a mix of good and bad news for mums, babies and future pregnancies.

The researchers found caesareans were associated with a decreased risk of urinary incontinence and pelvic prolapse for mums.

But women who went on to have further pregnancies appeared more at risk of miscarriage, stillbirth and a host of placenta problems.

And children born by caesareans appeared to have an increased risk of asthma for up to 12 years, and of obesity up to five years of age.

The researchers can't definitively say caesarean deliveries cause certain outcomes.

But they do say women and doctors should be aware caesareans have been associated with long-term risks, including future pregnancies.

"The significance that women attribute to these individual risks is likely to vary," the researchers said.

"But it is imperative that clinicians take care to ensure that women are made aware of any risk that they are likely to attach significance to."

Previous studies have looked at short-term health risks associated with caesareans, including surgical complications, increased likelihood of hysterectomies and death from blood clots.

This study attempted to plug a gap in knowledge about the longer-term risks, as caesareans delivery rates rise worldwide.

The study, which also involved the MRC Centre for Reproductive Health at the University of Edinburgh, and published in the journal PLOS Medicine.