When I was a medical student and junior doctor, the terms most commonly used to describe a vaginal birth without the use of instruments such as forceps or vacuum extractor were SVB (spontaneous vaginal birth) or SVD (spontaneous vertex delivery – the vertex is the top of the baby’s head).

Gradually, in the late 1980s and 1990s, there appeared in the lexicon the words “normal birth”. This was part of the reaction against the perceived high rates of interventions in pregnancy and labour, and the desire of women to take more control over their own bodies, something I support.

“Normal vaginal birth” has been polished and praised so much by now that it glows like a lighthouse beacon in much current obstetric and midwifery literature. But what exactly is “normal vaginal birth”?

Often used interchangeably with “natural birth” or “physiological birth”, normal birth is defined by the World Health Organization as a birth that is “spontaneous in onset, low-risk at the start of labour and remaining so throughout labour and delivery. The infant is born spontaneously [without help] in the vertex position between 37 and 42 completed weeks of pregnancy. After birth mother and baby are in good condition.”

Sounds great. Sounds as though if pesky doctors and midwives would just leave women alone they would get on with it. Lambs would gambol in green fields and Judy Garland would sing Over the Rainbow as the baby’s head crowns gently, with nary a tear in the perineum. The concept is espoused by maternity service groups in many countries, including Australia, particularly following the United Kingdom’s 2005 Campaign for Normal Birth initiated by the Royal College of Midwives.

For example, the NSW Health project Towards Normal Birth provides targets for reducing the numbers of caesarean sections, inductions of labour and other interventions, and increasing the number of “normal” births while also making care more women-centred and medical staff happier.

Let’s take a moment to think through the implications in the WHO statement. Pregnant women, to qualify, must not go into labour spontaneously before 37 weeks or have labour induced or a caesarean performed for any reason. Their baby must have a headfirst presentation and must not be too big to fit safely through the mother’s birth canal. No instruments can be used to assist vaginal birth, as happened with countless women I’ve delivered with the vacuum, the forceps or by caesar. They also must not bleed excessively.

Did all of these women, then, have “abnormal” births?

Human pregnancy and childbirth have evolved over millions of years to allow perpetuation of our species. As we were transformed from our primate ancestors, we switched to walking on two instead of four limbs; in the process our ability to give birth was refashioned, and its efficiency compromised. Our pelvises became narrower to accommodate walking upright, and the human foetus, especially the foetal head, became larger, as our brains became (potentially) more sophisticated.

During the later weeks of pregnancy and in the first stage of labour, that foetal head must slowly descend into the mother’s pelvis, gradually moulding and turning forward so that the widest diameter of the head fits through the widest pelvic diameter.

By the end of the first stage, the cervix must be fully dilated – wide open – so that the contractions of labour and the efforts of the mother can deliver the baby. Under the WHO definition, this must all take place without any outside assistance. The WHO definition doesn’t mention the woman’s pelvic floor or perineum, but from the final sentence it appears that these must remain undamaged for the birth to qualify as “normal”.

However, evolution itself, if considered as a process ensuring the survival of the fittest, has left in its wake a significant number of dead or damaged women and babies. For thousands of years childbirth was a very high-risk activity – for the ancient Egyptians, the Romans, the inhabitants of medieval Europe, and much later – and, with no really effective contraception until very recently, it was not a choice for women.

It was only from the 17th century onwards that any significant advance was made in reducing the waste of “natural” childbirth, with the arrival of forceps and ergot. Real progress was not made until the appearance of anaesthesia and antisepsis, a mere 150 years ago. The technical expertise developed in those 150 years – antibiotics, anti-D, ultrasound, safe surgery, oxytocics and many others – has now changed childbirth, at least in high-income countries, into a process that is inherently very safe for both mother and child. There is also the widespread availability of safe and effective contraception and safe legal abortion so that women can largely choose if they wish to bear children and when they wish to do it.

This safety, however, was achieved by the wholesale move of birth from the home into hospitals, and the increasing “medicalisation” of pregnancy and birth. By the middle of the 20th century, women were finding themselves marginalised in a hierarchical and patriarchal system that gave them little autonomy in regard to their own bodies. Part of their response has been the demand for more say in decision making, and for less medical intervention, in pregnancy and birth. The naturalistic and holistic aspects of childbirth, often in places away from hospitals and doctors, have been emphasised by some women and many midwives.

The physiological and psychological benefits of WHO’s “normal birth”, if it can be achieved, are undoubted. However, birth may start out as normal but then very quickly become “not normal”. And even “normal” births may so stretch and damage the pelvic floor or perineum that long-term incontinence and prolapse are the result.

Overzealous pursuit of “normal” birth has, in some instances, led to compromised safety and care of the mother and baby, with far-reaching consequences for the provision of maternity care generally. This certainly happened in the landmark UK case of Nadine Montgomery from Lanarkshire.

Montgomery’s son Sam was born in 1999 with cerebral palsy. Montgomery was awarded £5.25m compensation because doctors did not explain the risk associated with a normal birth in her case – she is small and a type 1 diabetic. Diabetic mothers can give birth to larger babies and one of the risks is shoulder dystocia, when the baby gets stuck during labour and can be deprived of oxygen, and suffer brain damage, which happened in Sam’s case. Her obstetrician did not discuss that risk and did not offer a caesarean section. It was a case that established that, rather than being a matter for the clinical judgement of the doctor, patients should be told whatever they want to know, not what the doctor thinks they should know.

We now have to ask the question: do the carers – midwives and doctors – have a right to promote “normal” birth when informing and counselling women about their birth options? The judges in the Montgomery case felt that this should be balanced by objective information about all of the alternatives to “normal” birth. And their decision to uphold Nadine Montgomery’s claim means that doctors and midwives now need to tell women, objectively, all sides of the story.

Medicine has come to compensate for some of the shortcomings apparent when birth is left entirely to nature. We now have many kinds of birth. Let us embrace them all.

This is an edited extract from The Women’s Doc by Caroline de Costa, Allen and Unwin, $32.99