The care that pregnant women receive depends upon where they live, a new report has concluded.
There is a "substantial variation" in practice between NHS maternity units in England, the Royal College of Obstetricians and Gynaecologists (RCOG) found.
The variation between different maternity units may suggest that not all women are getting the best possible care, according to the review conducted by RCOG and experts from the London School of Hygiene and Tropical Medicine.
The review highlights different rates of emergency caesarian sections, instrumental deliveries and episiotomy.
In some maternity units 8% of mothers needed emergency c-sections but in others the figure was 15%.
Almost one in five first-time mothers gave birth naturally but needed help with instruments in some units but in other units this figure rose to almost three in 10.
The number of women who needed an episiotomy ranged from 29% to 44%.
"We are concerned about the amount of variation identified in this report," said RCOG president Dr David Richmond.
"Although the exact causes are difficult to establish, it is paramount that maternity units have information about their services, as well as the ability to compare themselves to the national average and to their peers.
"The RCOG is dedicated to creating a culture of openness and transparency within maternity and gynaecological care. With this information, maternity services, alongside commissioners, will be able to move towards identifying priority areas for reducing variation and further improving the safety and quality of care provided to women and their babies."
Commenting on the report, Louise Silverton, director for midwifery at The Royal College of Midwives, said: "This latest report shows that there are still concerns about variation between maternity services and the care they provide.
"It is unfortunate that this continues and is mirrored in outcomes of still birth rate and perinatal deaths.
"While it is normal to see some variation in clinical practice, it must be remembered that it is women and babies who experience these variations in practice and there needs to be more information provided for women to enable them to choose where they want to have their care."
Health Minister Ben Gummer said: "Mothers and their babies deserve the very highest standards of care regardless of where they live.
"The NHS is already a safe place to give birth and by being open and honest about variations in care RCOG's report will help the NHS to improve the care it provides and build a safer NHS seven days a week."