"It hurts!" wails Karen King, gripping the rim of the birthing pool, her face contorted in agony. The midwife looks up from her file of notes. "I know," she says calmly. "It means you're getting there." From somewhere deep inside, Karen expels a shattering howl. It ricochets around the living room, where the paraphernalia of everyday life has been piled into corners to make space for the business of childbirth: latex gloves draped over a fruit bowl; a gas canister slung on top of a pile of unsent cards.

Water slops from the pool on to the parquet where, in a few days, a baby will hopefully be sleeping in a moses basket. Kevin, Karen's husband, strokes her hair from her eyes. "If I could, I'd swap places with you and take the pain myself," he whispers.

Karen moans. "What the hell was I thinking? I just want an epidural. Or a caesarean." Kevin and the midwives share a glance, unsure whether Karen is serious – which would mean an emergency transfer to hospital.

Between the waves of pain, though, Karen is clearly relieved to be at home and in control, instructing Kevin to get towels from upstairs, cushions from next door and pills from her bag. In the kitchen, champagne and pâté are chilling in the fridge. Upstairs, scented candles surround the bed, ready for when the new family curl up together for the first time.

A week earlier, Karen had been very clear on the reasoning behind their choice: "We're not hippies," she said, "but I'm pregnant, not sick, so why should I go into a hospital? Why go into an unfamiliar, clinical setting where you don't get continuity of care and are at risk of all sorts of other things like MRSA and swine flu?

"The best thing is that, after a home birth, I can shower in my own bathroom, then get into my own bed with my new baby," she added.

Yet there are medical experts who maintain that home births are dangerous and irresponsible. Some believe the practice is so reckless, it amounts to child abuse. So powerful is this anti-home birth lobby that not even Karen's hippies are choosing the option in great numbers any longer.

Until the advent of modern medicine, home birth was the de facto method of delivery. Long acknowledged to be safe for low-risk mothers, it is, when compared with hospital delivery, associated with fewer maternal interventions and a shorter recovery time. Women are less likely to haemorrhage, or to experience lacerations or infections.

Despite this, the practice has suffered a precipitous decline. In 1959, 34% of women gave birth at home in the UK. Last year, just 2.7% made the same decision. In Scotland, 1.2% of births take place at home. In Northern Ireland, this drops to fewer than 0.4%, while in the Republic of Ireland, the nursing and midwifery bill currently going through the Dáil will criminalise any midwife who doesn't take a woman to hospital 24 hours after her waters have broken, even though this can happen up to 12 hours before contractions begin and the labour might be proceeding well, requiring no medical intervention. Even in Wales, which in 2002 became the only country in the world to set a target for home births – 10% by 2007 – local authorities report rates varying between 1% and 3.8%.

Yet, low as they are, rates in the UK are still higher than across most of the developed world. In some US states, rates are down to 0.1%, while in the Netherlands – the country to which home birth campaigners have long looked for support and inspiration – numbers have plummeted from two-thirds in 1965 to less than a quarter today. Supporters of the practice say there is a very real possibility that legal home births will be eradicated in some countries in the very near future.

The overall picture is so bad, says Annie Francis, from Independent Midwives UK, she is tempted to believe there is a "global conspiracy against home birth". "That's probably not the case," she concedes, "but people get so vitriolic and polarised about home births that it's hard to have a sensible conversation. We need to ask the questions: how has medicalised childbirth become the default position? Where has this great fear of childbirth come from in the west?"

Back in Hertfordshire, Karen lies on the sofa, one leg slung over the back cushions, the other foot resting on the floor. "You couldn't, with any degree of honesty, say I'm unstressed or relaxed at the moment," she says, between waves of pain. "But in a hospital there would be beeping machines and strangers. I'm not saying this is great – but that would make it so much worse."

Philip Steer, emeritus professor in obstetrics and gynaecology at Imperial College London, has assisted at around 8,000 births and was an adviser to Nicholas Winterton's committee on health when it undertook an in-depth inquiry into maternity services in 1992. He insists he is not "anti home birth", but admits he "feels slightly frustrated when women's groups say most women should have a natural labour". Human birth is not as straightforward as many claim, he argues. "Over the last half a million years, the pelvis has become much smaller, to adapt to our upright posture. And because being brainy is such an advantage, our baby's heads have become much bigger. In some parts of Africa, this causes the death of one in six women from obstructed labour. In Nigeria alone, more than one million women are waiting for surgery to have their bladder repaired because of damage done by pressure of a prolonged labour during childbirth."

Problems in labour arise far more commonly than many people appreciate, Steer says. Around half of pregnant women in the UK will have or develop a complicating factor – from high blood pressure to diabetes – that makes a hospital birth advisable. Of the remaining half, he says, about 50% develop a problem during labour that may require an emergency transfer to hospital. "That can be very traumatic, even if things end up well."

For a moment last summer, it looked as though a new report would sound the death knell for home birth. The well-respected American Journal of Obstetrics & Gynaecology carried a meta-analysis of studies from several industrialised nations that concluded planned home births carried two to three times more risk of neonatal death than a planned hospital delivery. The findings reverberated across the world. In the UK, an editorial in The Lancet said the study "provides the strongest evidence so far that home birth can, after all, be harmful to newborn babies".

The editorial went on to claim the findings were so unequivocal that women should no longer have the right to choose a home birth: "Women have the right to choose how and where to give birth, but they do not have the right to put their baby at risk."

The reaction of the midwifery community was excoriating. Cathy Warwick, general secretary of the Royal College of Midwives, denounced the research as "flawed". Picking apart the study's methodology and findings, she concluded it was "a deliberate attempt to undermine home births".

The AJOG is now backpedalling. "Due to an enormous amount of correspondence we have received raising concerns over this article, it is undergoing a careful review," says Thomas Garite, the journal's editor-in-chief. "We would prefer not to comment until that review is completed."

The debate is muddied by the fact that evidence for outcomes of newborn babies delivered at home is contradictory: data comes from small, observational studies, and frequently includes misclassified cases – such as the actual rather than the planned delivery location. Even vital facts, such as perinatal mortality or caesarean rates, cannot be compared because of variations in how the data is collated and defined.

In the face of such confusing messages from the medical community, women such as Karen, who choose to have their first child at home, are increasingly rare. Marie Martin's first child, Alexandra, was born in hospital in 2007. "I had wanted the security of a hospital birth, but it turned out to be anything but reassuring," she says. "Instead, I found it very distressing and disempowering. There were lots of drugs involved, and an overwhelming feeling that I was not in control, a feeling that I am certain contributed to the postnatal depression that dogged me for the first year of motherhood."

When it came to giving birth to Alex's brother, Philip, in October, she decided to deliver at home. "I have to admit that the home birth was not the experience I thought it would be, either," she says. "It was really painful and hard work. I didn't feel particularly empowered. But it was miles better than being in hospital – and when we were left alone, minutes after Philip arrived, in our own home, the family bonding was unbelievably intense and wonderful. I have never experienced such unadulterated joy. We were all literally weeping with happiness."

The experience is not always so blissful, however. When Kim Mussell gave birth to Daisy, her second daughter, at home in south London five years ago, she ended up with an infection so serious she nearly died: "The midwife made me give birth in a position I wasn't comfortable in, which meant I tore really badly. She stitched me up, but there was internal damage she missed. I ended up in hospital on a drip for a week and having to undergo reconstructive surgery."

Karen's home birth doesn't go to plan, either. By the time the midwives have been with her for three hours, she is ready to give up. "I can't take this pain. I'm sorry, everyone, but I don't think I'm going to make it. I would rather have the drugs right now than be at home."

Depending on one's interpretation, the midwife is either calming – or reluctant to admit defeat. "Do you really, really want that?" she asks. "Why don't you listen to some music instead?"

Karen doesn't have the strength to argue. They agree to compromise: the baby has two more hours to show up. After that, Karen will go to hospital and take every drug she can lay her hands on.

The decline in UK home births began after the Peel Report of 1970, which said every woman should have the right to give birth in hospital. As Professor Steer says, "I'm old enough to remember the 60s, when women marched in the streets, demanding more places be made available for hospital births." But it took less than a generation for women to realise what they had lost: by 1992, a survey by the expert maternity committee found that 72% of women said they wanted an alternative to a hospital delivery. Of those, 44% were interested in home birth.

The government, the Royal College of Obstetricians and Gynaecologists, and the Royal College of Midwives came out in support of greater choice for women, including access to home births. Britain's maternity services were duly transformed. The conundrum today is why, despite 50% of women regularly polling as being in support of the practice, the take-up is still so low.

"You need three things in order for women to be free to choose home births," says Dr Leonie Penna, a consultant in foetal medicine and obstetrics at King's College hospital. "You need women who want a home birth, you need a supportive infrastructure and you need midwives who are happy to deliver it. Unfortunately, we obstetricians undermine the first two – and sometimes even all three. By our nature, we are very risk averse. Many of us blow out of proportion the risk inherent in home births, counselling women against it in a very paternalistic way. The fewer women chose it, the more the infrastructure is weakened. Then midwives begin to lose confidence, and suddenly the entire structure becomes shaky."

The risks are not just health-related. Disputes involving obstetricians now account for almost two-thirds of the annual £800m NHS medical litigation bill. That means that about 15% of the current maternity budget is going to lawyers and clients: an almost tenfold increase in 11 years. "Cerebral palsy victims – one case in six of which are associated with mistakes during labour – can each get £6m or more, and I know of private sector obstetricians faced with insurance premiums of £100,000 or more a year," Steer says. "It is inevitable that everyone wants to play safe."

Perhaps most crucially in the UK, there simply aren't enough midwives: the small increase in numbers over the past few years has nowhere near kept pace with our historically high birthrate, itself complicated by increasing numbers of obese and older women, who are likely to need more medical attention. Against this backdrop – and despite the onus on trusts to provide home births for any low-risk woman who wants one – women are finding they now have only very limited access to them in parts of Britain, with midwifery services often withdrawn at short notice.

Karen is one of the lucky ones. For her entire labour, she has the dedicated attention of two NHS midwives. Armed with just gas and air and a Tens machine, they respond to Karen's pleas for drugs with the suggestion that she tries a birthing ball – "Or perhaps we could all sing a song?" Karen growls at this suggestion, while Kevin ducks his head to hide a smile.

But this well-staffed, relatively laid-back home birth is not available to every mother. And, according to Mary Newburn, head of research and information at the parenting charity the National Childbirth Trust, unless at least 5% of women choose a home birth, the practice will never gain the momentum required to steamroller the necessary infrastructure into existence.

In the Netherlands, however, where the infrastructure does exist, home birth rates have nonetheless "dropped like a stone", according to Professor Simone Buitendijk, head of the child health programme at the Netherlands Organisation for Applied Scientific Research. Confidence faltered after the death rate among newborn babies failed to decline as fast as in some other European countries. A series of media reports raised questions about the safety of home births, culminating in a leading national newspaper running a front-page splash entitled: "Don't Try This At Home."

"Soon, there will not be enough demand to justify the infrastructure," Buitendijk says. "Then the system will collapse – and let there be no misunderstanding: we won't be able to rebuild it."

In other countries, midwives face prosecution for delivering babies at home. Just last month, Hungarian midwife and home birth expert Dr Agnes Gereb was sentenced to two years in prison for malpractice, after a mother went into early labour in her birthing centre. The judge also found Gereb guilty of medical negligence in two other home births, including one in which the baby died.

The sentencing came just weeks after the Hungarian government finally decided to regulate home births. Until last month, women in Hungary have had the right to give birth at home – but medical professionals were banned from assisting at planned home births. Home births will now be allowed from 1 May, but only under strict safety conditions. Whether, after Gereb's sentencing, there will be any midwives prepared to take the risk is another question.

For a brief period last May, it even became illegal to have a home birth in New York City. Under a "written practice agreement" system introduced in 1992, midwives in New York state are obliged to be approved by a hospital or obstetrician. Only one hospital – St Vincent's in Manhattan – was prepared to do that. When it went bankrupt on 30 April 2010, the city's midwives were unable to find another institution willing to underwrite them.

Overnight, the city – which already had a home birth rate of just 0.48% – was left without a single midwife legally able to help a woman give birth in her own home. A mass public protest led to the passing of the Midwifery Modernisation Act, which allows midwives to work free from the control of obstetricians. But the American College of Obstetricians and Gynaecologists continues to denounce home births. Choosing to have a baby at home, it says, is to show preference for the process of giving birth over the goal of having a healthy baby.

In a statement, it said: "We do not support programmes that advocate for, or individuals who provide, home births. Childbirth decisions should not be dictated or influenced by what's fashionable, trendy, or the latest cause célèbre."

Back in the King house, Karen has managed without drugs – although it has been a close call on a number of occasions. At 2.40pm, almost exactly four hours after Kevin called the midwives, Karen rises from the sofa like Gaia. Throwing her legs apart, she squats with her hands on her hips and turns her face upwards. There is a sudden silence in the room. All attention is focused on Karen but she is elsewhere, straining against the pain of the contractions.

At 3.12pm, the baby's head appears. Beside himself, Kevin rubs Karen's thigh, her shoulder, her forehead: "Hey, baby! Hello. Hello, gorgeous!" he weeps.

Together on the sofa, the new parents look like children themselves: gleeful, astonished and amazed. "Oh dear God," breathes Karen. "I didn't think I was going to make it. Hello, baby. Hello, Agatha Florence Fenella King. It's OK: Mummy's here. Daddy's here."

But that is not the end of the story: an hour after giving birth, Karen has still not delivered the placenta. An injection of syntometrine proves useless. The placenta refuses to appear. Agatha suckles and is weighed – 6lb 9.5oz. She is measured and her temperature taken. But the atmosphere in the room has changed. It is no longer celebratory. At last, an hour later, the midwife gives up hope. The ambulance and paramedics are called.

Karen struggles to take a balanced view. "It seems so unfair that I have to have an epidural now, when I didn't have it when the pain was so indescribably awful," she says weakly.

Seventeen minutes later, an ambulance pulls into the driveway. The front door bangs open and a blast of cold air accompanies the bustling paramedics into the room. They immediately take control.

Still bloodied and dazed, Karen must hand over her baby and be led outside. As she lies alone in the back of the ambulance – parents are not allowed to make emergency transfers with their babies – there is a second flurry of panic in the house. Unbeknownst to Karen, Agatha has stopped breathing.

In the living room, Kevin stares mute and helpless as his child turns blue on the sofa in front of him. The midwife swiftly resuscitates the baby and, as colour floods back to her face, a second ambulance is called. Agatha is out of danger, but will be checked over at the hospital, just in case.

A paramedic goes outside to tell Karen what has happened, speaking so skilfully she barely has time to register that her daughter was in danger before understanding that she is now safe. Her ambulance speeds away into the night, leaving an ashen-faced Kevin tightly clutching his daughter – a tiny bundle, swaddled in thick, red blankets.

While the paramedics and midwives exchange notes back in the house and quickly clear up their equipment, Kevin is left alone to climb into the back of another ambulance. There he waits, until the doors are closed and he, too, speeds away.

Distressing as it might be, this is not an unusual outcome for home births: around 40% of first-time mothers who plan to deliver their child at home end up being transferred to hospital.

It is for this reason that some experts, including Professor Steer, believe home births are suitable only for those who have previously had an uncomplicated pregnancy and a healthy baby: about a quarter of pregnant women. There is, however, no evidence that emergency transfers put the mother or baby at any risk. The Confidential Enquiry by the National Birthday Trust into every UK home birth in 1994 found that, though the 769 mothers and babies who were transferred included two stillbirths and two neonatal deaths, "the outcome was satisfactory for the baby in the vast majority of cases".

Back at home, the day after the birth, the Kings are exhausted and dazed, but don't regret their decision. "At least we had a chance of experiencing what would have been, for us, the perfect birth," Karen says. "We lost nothing by trying: we ended up in hospital, which is where we would have been had we opted for that in the first place."

In fact, the few hours Karen spent in hospital merely confirmed her suspicions. "I was right: hospitals stress me out. Despite everything, I'd try for a home birth again next time."

Agatha shifts in her cot and lets out a contented sigh. Her parents look over at the sleeping child, almost in surprise. "I keep forgetting that she's actually here: that we've really got this wonderful, beautiful baby," says Karen. "We've finally got our family."