The largest ever survey of maternity care in England has found widespread failings, with services in London criticised as the worst, the government's health watchdog said on Friday.
The Healthcare Commission said many women were receiving inferior screening of their unborn babies. It said there were too few midwives to provide one-to-one care during labour.
Four out of ten pregnant women failed to get all 11 recommended checks on their babies during ultrasound scans, which include tests on the baby's heart, face and lips.
Only 11 percent of hospital trusts said they had met higher quality requirements set for Down's syndrome screening in April last year.
Staffing was found to be below levels recommended by professional medical authorities, who advise that 36 midwives are needed per 1,000 deliveries to meet the government's target of one-to-one care for all women in labour.
The average level of midwife staffing in maternity units was found to be 31 per 1,000 deliveries. Nine trusts had just 26 or fewer midwives per 1,000.
The watchdog surveyed all 148 hospital trusts providing full maternity services in England, responsible for around 600,000 births a year.
The best performing maternity units were in the north of England, with Stockport NHS Foundation Trust the best of all.
Maternity services in London and central England were the lowest rated, with West Hertfordshire Hospitals NHS Trust receiving the worst score.
Health Commission Chief Executive Anna Walker said she was concerned about London's poor performance.
"There are a number of factors that may have influenced these results, such as lower staffing levels and the mobility and mix of the population. But London trusts need to rise to these challenges."
She said low ratings did not mean a maternity service was unsafe.
The Liberal Democrats called for an immediate review of maternity staffing capacity.
"With the birth rate rising, many midwives set to retire and not enough jobs for those newly qualified, the situation will only get worse", said the party's Health Spokesman Norman Lamb.
Births have risen by 72,000 since 2001, while there was a fall in the numbers of midwives last year.
The NHS Confederation, representing 95 percent of National Health Service organisations, said it recognised that the survey had revealed "deep concerns" about maternity services.
