The government has guaranteed to employ an extra 3,400 midwives
Many health authorities are not on track to provide the midwives needed for one-to-one care, figures obtained by the midwives' trade union suggest.
The Royal College of Midwives wants one midwife for every 28 births, but says only four Strategic Health Authorities (SHAs) will hit or better this by 2012.
Four of England's 10 SHAs will still have more than 32 births per midwife by that time, NHS workforce figures show.
NHS guidelines stress all labouring women should have a dedicated midwife.
In order to achieve this, the RCM believes a full-time midwife is necessary for every 28 births per year.
It says that while the government has guaranteed to employ an extra 3,400 midwives by 2012, in fact an extra 5,000 are needed "to deliver safe, high quality care".
This would ensure cover for antenatal and postnatal support - including help with breastfeeding - as well as delivering babies. It would also account for sick and maternity leave, the college states.
Other unofficial calculations have said a maximum of 32 births per midwife is acceptable, but four SHAs look likely to exceed this.
They include Yorkshire and Humber - with 33.8 by 2012 , East Midlands - with 33.9, East of England - with 35.2, and London - with 33.6.
With the exception of Yorkshire and Humber, these are nonetheless an improvement on current ratios.
There has however been growing pressure on maternity services due to the rising fertility rate - the result in part of women having babies older and immigration levels. At the last count, nearly 25% of live births were to mothers born outside the UK.
RCM general secretary Cathy Warwick said: "We know the government is making a big effort to recruit more midwives and are putting money into maternity services.
"Their policies are good and are going in the right direction. However, these figures show that although the situation for most regions will be better, it will still not good be good enough to deliver the quality of care women need."
She called for a "step change" at regional level to recruit more midwives, adding: "We hope that decision makers at regional level will take responsibility for this, treat it as a priority and put money they have been given for maternity services into maternity services."
Caroline Waterfield, deputy head of employment services at NHS Employers, said: "It is important that Royal Colleges and professional bodies issue expected standards required by both clinical staff and NHS trusts to ensure the safety of patients.
"However, while ratios recommending appropriate staffing levels are a helpful guideline for those providing midwifery care there needs to be local flexibility for employers to take into account local need and the intensity of individual units."
A Department of Health spokesman said: "The government is committed to the provision of high-quality, safe maternity care for women and their babies.
"In 2007-08, we invested £1.78 billion on maternity services. In January 2008, we announced a further £330 million for maternity services for the next three years.
"We are aware that different parts of the country face different challenges, and that some areas have further to go than others, but expect to see real improvements in maternity services across the country over the next year."