The government has guaranteed to employ an extra 3,400 midwives
Maternity services in England are at a critical point, the leader of the midwives' union says.
Speaking ahead of the Royal College of Midwives' annual conference, Cathy Warwick said progress was being made.
But she added the target to give women a choice of where to give birth looked like it would be missed, while there were signs budgets were being squeezed.
The government said extra money was being invested and staff recruited, proving maternity care was a priority.
Labour's manifesto promise at the last general election was that by 2009 all women would have a choice over where and how they have their baby and what pain relief to use.
The party also said that every woman should be supported by the same midwife throughout her pregnancy.
While some aspects of this look like being met, choice of a home birth, hospital delivery or midwife-led birth unit was proving more difficult, Professor Warwick said.
She said surveys suggested full choice was only offered in about 50%of cases.
She said services were also struggling to cope with the spiralling birth rate - it has jumped by 20% since 2001.
Staffing numbers have also increased, but by less than 10%, leaving the health service short of 5,000 in total, the union believes.
The government has promised to recruit an extra 3,400 midwives in the coming years, but Professor Warwick said: "I think we have reached a critical point. Extra money has trickled down, but not enough.
"We need to make sure we get extra midwives into the NHS, but some places are seeing budgets cut and staffing shortages.
"The rising birth rate means that services are struggling to develop and maintain a range of care."
She said ante-natal and post-natal care were particularly vulnerable at a time when the NHS budget was likely to see a freeze or even a cut in the coming years.
But she also pointed out that students were struggling to find jobs - a survey carried out for the conference revealed 75% were not confident of finding a position.
Her comments come as nearly 1,000 midwives gather in Manchester for the two-day conference.
Also attending will be Health Secretary Andy Burnham and shadow health secretary Andrew Lansley, who will set out their visions for future care.
Mr Lansley, in his speech on Thursday, is expected to promise more funding for community services and rural areas as a whole.
He will also say the NHS funding system has created a perverse incentive to encourage hospitals to carry out Caesarean sections instead of natural births.
He will say: "Labour haven't delivered on their promises to give women real choice, to provide proper care during pregnancy and following birth."
But the government defended itself against criticisms.
Health minister Ann Keen said an extra £330m - about a sixth of the overall maternity budget - was being invested into services.
"All women can expect individual support from a midwife, supported by a wider maternity team throughout her labour and birth."