"I was mortified and cried, because I had prepared myself for a natural birth" ... Tracy Hart cradles her son Saxon, who was born by caesarean section. Photo: Steven Siewert

"I was mortified and cried, because I had prepared myself for a natural birth" ... Tracy Hart cradles her son Saxon, who was born by caesarean section. Photo: Steven Siewert

Tracy Hart had intended to have her first child, Ariane, now 2½, naturally. But when Ariane failed to move into the normal birth position, Mrs Hart was told that a caesarean was the safest option.

Second time around, Mrs Hart, 35, was eager to try again for a natural birth, but at 41 weeks and two days into her pregnancy, she still had not gone into labour. A caesarean was ordered - because doctors thought an induction might have been too hard on her scarred uterus - and four days ago son, Saxon was born at Royal North Shore Hospital.

Though delighted with her ''happy and healthy'' 4.6-kilogram son, Mrs Hart said, ''I was mortified and cried, because I had mentally prepared myself for a natural birth. A lot of women who don't have any problems giving birth don't realise some women just don't have a choice.''

First-time mothers with no obvious health problems, and subsequent births like Mrs Hart's where the first was by caesarean, are overwhelmingly the biggest contributors to the NSW epidemic of caesarean births, state data shows for the first time.

Twins, and babies in the breech or other difficult positions in the uterus, account for a much smaller proportion of the one in three babies now born by caesarean section, according to the University of Sydney study of all 244,822 caesareans conducted in all state hospitals in an 11-year period to December 2008.

During that time, the overall caesarean rate increased from 19 to 30 per cent of all births. But subsequent caesareans increased much faster, at an average 5.3 per cent a year during the study period.

Among first-time mothers, caesareans grew fastest - on average 6.8 per cent a year - among those who did not go into labour or whose labour was induced, suggesting a big rise in planned procedures. Among first births where the woman went into labour and later delivered surgically, the increase was only 3.5 per cent a year.

Jonathan Morris, a study leader and professor of obstetrics and gynaecology at the university, said the new data provided the first comprehensive state-wide picture of factors behind the surge in caesareans, which NSW Health has pledged to bring back to 20 per cent of all births by 2050. It suggested that concentrating on promoting normal birth among first-time mothers would have the biggest impact on reducing the overall rate, Professor Morris said.

The research, published in the journal BMC Pregnancy and Childbirth, showed it was highly unlikely the increase in caesareans could be legitimately attributed to complications such as the older age and the increase in overweight mothers, he said - because most of the rise had occurred in women with apparently few medical risks.

The president of the Australian College of Midwives, Hannah Dahlen, said ''we need to dramatically improve the evidence-based advice given to mothers after they've had a caesarean section [to] emphasise the risks rather than just the benefits of repeat [surgery]''.