Expressing milk late in pregnancy before the baby is born is safe for diabetic women, a landmark study has found.

A landmark study has shown it's safe for diabetic women to express breastmilk during late pregnancy, dispelling fears it can lead to early labour.

Nearly half of all babies born to a mother with diabetes will develop potentially dangerously low blood sugar levels, known as known as hypoglycaemia, soon after birth.

This can affect a baby's brain development and lead to seizures and even brain damage.

The best way to stabilise blood sugar levels is feeding the baby breast milk, says Professor Della Forster from La Trobe University's Judith Lumley Centre and the Director of Midwifer and Maternity Services Research at the Royal Women's Hospital.

However for many women who experience diabetes during pregnancy their milk comes in late.

Despite widespread enthusiasm for antenatal expressing, previous studies had suggested the practice posed potential harm for the baby and mother.

But Professor Forster says they can now "confidently" say it is safe for low-risk diabetic pregnant women.

"Our research fills a significant global gap in knowledge and provides much-needed guidance to pregnant women around the world and those providing maternal care," Prof Forster said.

According to the study published in The Lancet, most of the 600 participants safely expressed milk from 36-37 weeks of pregnancy and produced enough milk ahead of the birth to feed their baby adequately.

The mothers expressed an average 20 times before birth and on average produced 5mls of milk each time in total for the whole time of expressing.

Expressing also led to an increased proportion of mothers who exclusively used breast milk to feed their child for the first seven days after birth.

This is very positive, says Professor Forster, because it reduces the child's risk of developing diabetes later in life.

"If your mother's had diabetes during pregnancy then your're more likely to develop diabetes later in life and if you have exposure to formula early in life that makes you more likely to develop diabetes later in life," she said.

Sue Walker, Professor of Maternal Fetal Medicine at the University of Melbourne and Director of Perinatal Medicine at Mercy Hospital for Women, says the findings allay any fears the practice puts the mother or their baby at risk.

"These findings do not apply to higher risk women, but provide invaluable data that could be used for further research," Prof Walker added.