Women in labour are being made to feel like cattle or like they are on a conveyor belt due to midwife shortages, a new report warns.
A lack of staffing leaves some women frightened and half experience at least one "red flag" event such as not getting timely access to pain relief.
The study, from the National Childbirth Trust (NCT) and the National Federation of Women's Institutes (NFWI), is based on a survey of 2,500 women who have given birth since 2014.
It found that, since a similar report four years ago, there has been "scant progress" in women's experiences of giving birth on the NHS.
Half of all women surveyed experienced at least one "red flag" problem, which is defined by the National Institute for Health and Care Excellence (Nice) as being a "warning sign that something may be wrong with midwifery staffing".
Problems include delays of 60 minutes or more in washing or suturing, medication doses being missed, delays of 30 minutes or more in getting pain relief, or when one midwife is not able to provide continuous one-to-one care and support to a woman during established labour.
The new report found that 17% of women did not get such one-to-one care from midwives. Some 31% of women who required or received pain relief experienced a delay of 30 minutes or more, and 15% said there were delays in their immediate post-birth care, such as washing or suturing.
Meanwhile, 28% of women who needed medication either during or following the birth experienced a delay.
The survey also found that 89% of women saw between one and six midwives during their pregnancy, with most seeing between one and four.
Some 88% of women had never before met any of the midwives who looked after them during their birth, although 52% said this did not make a difference to them, mainly due to the professionalism of the midwives caring for them.
But 12% said this made them feel alone and vulnerable, and 6% said it made them feel unsafe.
Several women wrote about feeling like "cattle" or "a machine".
One said: "I received a very 'robotic' care. It wasn't very personal and I felt like just another person on the conveyor belt."
Another said: 'I wasn't treated as a human. I was just a product on a conveyor belt. I was not respected and my birth has left me suffering post traumatic stress disorder."
Another pointed to staffing issues, saying: "My chosen hospital ward and adjoining birth centre were extremely busy, or so I kept being told on the phone, which resulted in me having an unplanned home birth."
One said: "There was no room for me on the delivery ward. I ended up giving birth in the antenatal ward, which meant I couldn't get either a water birth or an epidural. Disappointed not to have had the labour I wanted because of staffing issues.'
Once women had given birth, almost one in five (18%) said they did not see a midwife as often as they needed.
Of these, 36% said it caused them great concern and a further 32% said it caused them a small amount of concern.
Some 31% of women said the diagnosis of a health problem was delayed due to lack of care after birth, while 29% had to go to their GP, A&E, or walk-in centre instead.
Issues with feeding the baby was the most-cited concern, followed by a woman's desire to speak to a midwife about her own emotional and mental wellbeing, followed by issues with stitches and sore nipples.
Marylyn Haines Evans, chairwoman of public affairs at the NFWI, said: "The findings from this report show that chronic midwife shortages, an estimated 3,500 in England alone, continue to undermine the delivery of high-quality care for women and their families.
"Half of the women we spoke to reported red-flag events during their care, suggesting that staffing levels are at crisis point."
Elizabeth Duff, senior policy adviser at the NCT, said: "Our research has exposed a crisis in maternity care. No women should have to suffer a red flag event when bringing a baby into the world. Severe staffing shortages must be acted on so that every family receives an acceptable level of care."
Louise Silverton, director for midwifery at the Royal College of Midwives (RCM), said the report should be a "red flag event for this Government".
She said: "The fact that half of women have experienced a red flag event is hugely worrying. It is a sign of services under too much pressure, with too few resources and not enough staff.
"This ongoing shortage of midwives and underfunding of services is not delivering the service that women and their families need, and it is storing up health problems for the future that could be prevented."
Professor Mary Ann Lumsden, senior vice president of the Royal College of Obstetricians and Gynaecologists, said: "Stretched and understaffed services affect the quality and safety of care provided to both mothers and babies and this report highlights the extreme pressures faced by our maternity services.
"Currently there are serious shortages of maternity doctors due to gaps in middle grade rotas approximately 30% of the time, which means that many units are dangerously stretched presenting risks of burnout.
"Further investment in maternity services will help ensure that women have access to comprehensive services from pre-conception to motherhood and beyond."
A Department of Health spokesman said: "We want the NHS to be one of the safest places in the world to have a baby.
"There are over 1,500 more midwives on our maternity units since 2010, and more than 6,300 currently in training, with our changes to student funding creating thousands more training places by the end of this parliament."