Many expectant mothers are not getting the best possible care during childbirth, experts said after research showed wide variations in maternity care practice.
The number of women who have to undergo induced labour or instrumental deliveries is twice as high in some hospitals compared to others, figures show.
The Royal College of Obstetricians and Gynaecologists (RCOG) along with the London School of Hygiene and Tropical Medicine examined data concerning English hospitals in 2011/12.
They found that among women giving birth for the first time, there was a two-fold difference between hospitals with the highest and lowest rates of induction of labour, with the lowest having 17% of new mothers being induced and the highest having 38%.
The figures also show that in some areas 20% of first time mothers had to have an emergency caesarean section after induction of labour compared to 40% in other areas.
And they found that the number of new mothers who had instrumental deliveries varied from 16% to 32%.
The RCOG said the variation may be a "source of concern" as it could suggest that "not all women are getting the best possible care", or that NHS resources are not being used in the most efficient way.
But the report's authors cautioned against over-interpreting the findings because the variations could be accounted for by other variables or the quality of data submitted by the hospitals.
"The initial set of indicators suggests wide variation in both practice and outcomes between maternity units which is a source of concern for the specialty as we cannot be sure that every woman is getting the best possible care," said RCOG vice president Dr David Richmond.
"It highlights that specialist-delivered care must expand so that for women with complex obstetric needs - which may only become apparent during labour - care can be provided by trained clinicians 24 hours a day and seven days a week.
"There is a need to improve the completeness and consistency of routine maternity data and we hope that this report will act as a stimulus for clinicians and units to improve their data collection activity which will ultimately lead to improving the quality of patient care."
Mervi Jokinen, practice and standards development adviser at the Royal College of Midwives (RCM), said the report "gives professionals working in maternity services useful comparative data of current variations in performance".
She added: "Such data encourages maternity professionals to look at the way they are working and to consider how they can improve the services they provide for women.
"The report is open and transparent about its limitations which should drive all involved in maternity care to improve data collection and agree on universal data definitions.
"We will be looking at the report carefully and considering how the RCM can help to ensure that women receive the same quality of care and the best possible outcomes wherever they deliver."
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