Women have been doing it since the dawn of time, yet at the start of the 21st century we still don't know the risks of the different modes of childbirth.
This matters to the millions of women a year who give birth. A bad experience in childbirth can cast a long shadow over parenthood.
So, which is safest - a caesarean section or a vaginal birth?
The vast majority of women will give birth safely, happily and without incident, whatever the mode of delivery.
Only a minority will suffer side-effects - but these can be serious.
A caesarean involves an abdominal operation which carries risks from the general anaesthetic (if there is one), infection and the long-term psychological and physical effects.
A vaginal birth, with or without intervention such as forceps, carries risks of damage to the pelvic floor, incontinence and loss of sexual function.
This, of course, is to consider only the risks to the mother. Most women would gladly accept an increased risk to themselves if it reduced the risk for their baby.
But, except in very rare cases where the survival of one is incompatible with the survival of the other, the interests of mother and baby are interdependent. A good birth for one will be good for the other.
Good or bad trend?
What, then, is a good birth?
Judging by the statistics, an increasing number of women and their doctors think it requires a Caesarean.
Twenty years ago, fewer than one in 10 births was by caesarean in England (9 percent) according to health department estimates. By 1997, that figure had risen to 17 percent.
The interesting question is whether this trend is good or bad. The answer is that it depends who you ask.
Childbirth is an emotional as well as a physical rite of passage, and it arouses strong passions.
Some see the growth of Caesareans as the worst example of the medicalisation of childbirth, driven by the fear of litigation.
Others argue that it is the modern way to give birth, using technology to provide a safer and pain-free delivery.
There are strong cultural determinants.
Northern European countries tend to have lower Caesarean rates than the UK, while in southern Europe the rates are higher.
Avoid complications
In 1997, when the UK rate was 17 percent, the Netherlands had a rate of 10,4 percent and Norway 12,3 percent. In Portugal the rate was 27 percent.
In South America, where protecting sexual function is a high priority for middle-class professional women, some private hospitals have caesarean rates of up to 80 percent.
In the UK, a survey of female obstetricians in London found that 30 percent would opt for a caesarean to avoid the complications of normal childbirth.
They, however, are the ones who see the complications. It is hardly surprising that the traumatic deliveries they have to deal with drive them to opt for the relative safety of a caesarean in their own case.
A subsequent survey of midwives, who deal with normal births and consequently have a less critical view of the risks, found that 95 percent would opt for a vaginal delivery.
Midwives also care for women who have had caesareans, and witness the problems they face.
Respect womens' choices
Where does that leave pregnant women? Two years ago, Sara Paterson-Brown, consultant obstetrician at Queen Charlotte's hospital, London, suggested in a controversial article in the British Medical Journal that women be given the choice of how they deliver.
Although doctors frowned on the idea of allowing them to choose a caesarean on demand, without any sound clinical reasons, to fit in with busy lives and avoid the pain and unpredictability of labour, there was no reason to resist them.
She argued that government reports such as Changing Childbirth, published in the early 1990s, had urged doctors to respect womens' choices in maternity care, and it was unfair for their choices to be discredited because they were not the ones expected.
"We are at a turning point in obstetric thinking brought about not only by advances that have made Caesarean section safe... but also by the attitudes of society which reflect intolerance to risk.
"We encourage family planning, pre-pregnancy counselling and ante-natal screening... can we do all this and refuse a woman a safe mode of delivery?"
Risks are emerging
But is it safe? The risks of vaginal birth include damage to the pelvic floor and to the urethral and anal sphincters, which can result in incontinence and an increased long-term risk of prolapse of the genitals.
These risks have been hidden for years because women have been too embarrassed to admit to them.
Now they are beginning to emerge, and some doctors claim the scale of the damage caused by childbirth is much greater than has been supposed.
However, it is still unclear whether the damage is caused by the baby coming though the pelvic floor in delivery or whether it is earlier, during labour, when the nerves in the region are squeezed.
If that is the case, only a planned caesarean performed before labour begins would avoid the harm.
Guilt
On the other hand, caesareans carry a 10 times higher rate of hysterectomy due to haemorrhage. There is also a risk of a low-lying placenta threatening any subsequent pregnancy.
In some women, feelings of inadequacy, guilt and failure in not completing a natural process may affect bonding between mother and child, especially if the operation is conducted under general anaesthetic.
Professor James Drife, consultant obstetrician at St James University Hospital, Leeds, said: "We are used to women being fed up at the end of pregnancy and saying to the doctor, please give me a Caesarean and let's get it over with.
"The standard response has been to say hang on a bit and encourage them that they can get through it.
"Now women are coming in with a plan and saying this is what they want. They are becoming empowered and better able to ask for what they want.
They are still a minority and they wouldn't explain the rise in the caesarean rate, but they are one end of the spectrum."
Women who give birth undergo an experience of great emotional intensity. The experience frames their view of motherhood and of the medical profession that helps bring their offspring into the world.
Getting it right matters in every area of medicine, but nowhere more than in the area of childbirth.