Obstetricians in NSW public hospitals will receive strict guidelines this week about when they should induce labour, after a state-wide surge in the practice that may be responsible for a continuing rise in caesarean births.

Among women aged 20 to 34 who had their first baby in 2009, 34 per cent were induced - a record high which represents nearly 3 per cent more women than the previous year.

And for the first time, three hospitals induced more than half of mothers in this category, according to new figures released on the Ministry of Health's website.

Overall, more than a quarter of all deliveries were induced, using techniques that raise the risk of needing a caesarean section because they speed the birth process and make it more difficult.

The Chief Health Officer, Kerry Chant, said the directive would establish ''clinical parameters around the use of oxytocin'' - the hormone that triggers contractions and is the most widely used form of birth induction - for women of different ages with a range of medical conditions. But doctors would still have discretion in individual cases.

The move comes as the statistics show the state has failed to rein in the rate of caesarean births, which in 2009 escalated to 30.2 per cent of all deliveries, from 29.5 per cent the previous year - about an extra 700 babies.

Forceps and vacuum extraction deliveries have also increased, accounting for 11.2 per cent of all births in 2009, while normal vaginal deliveries fell to 58.2 per cent.

Private hospitals' induction rates were generally higher than in the public system and their caesarean rates were dramatically higher, especially among younger, first-time mothers - more than 40 per cent of whom underwent surgical birth at two hospitals.

The president of the Australian College of Midwives, Hannah Dahlen, said 55 per cent of first-time mothers who were induced would then require a caesarean or forceps delivery, and the chance of delivering vaginally in future was dramatically reduced.

Caesareans are recognised to cause complications for babies and to make subsequent pregnancies more dangerous. A policy introduced in public hospitals last year to promote normal births might turn the trend around.

''I hope what we're seeing in 2009 is the worst it's going to get,'' Associate Professor Dahlen said. But it did not apply to private hospitals.

Women who chose private hospitals were rarely aware of the impact on their chance of delivering naturally. ''I don't think women know these figures exist,'' she said. ''They look for [a hospital] nearby and they think about how the room looks and the environment.''

Alec Welsh, the chairman of the NSW regional committee of the Royal Australasian College of Obstetricians and Gynaecologists, said some hospitals had become less inclined to let women aged over 40 wait even a day beyond their due date, as research indicated this might increase the risk of stillbirth. But women were not always advised that the absolute risk was still very low, Professor Welsh said.

As well, some hospitals had begun to induce women with moderately high blood pressure, in the absence of other complications.

Professor Welsh said doctors needed to be alert to circumstances in which induction was safer but should not ''change practice too easily in the light of isolated publications and [research] trials … it's hard to see how 50 per cent [of women in some hospitals] could be sufficiently outside the norm to warrant induction''.