Should mothers be encouraged to follow their instincts during labour, or do the professionals know best?
"Now, when you feel that contraction, I want you to hold your breath and really push ... push hard, right down into your bottom ... right? Keep it going, keep pushing, push, push ... don't waste the contraction! If it's still there, give another push.

"If you give us some nice long pushes, it'll be out in half the time ... "

It's the second stage of labour, just prior to the birth, the midwife is exhorting the mother to take a deep breath, to hold it for as long as she can, and to make huge, expulsive efforts, to "come on and get that baby OUT", as one said to me during the birth of my second child.

Technically, this hold-your-breath-and-push-when-I-say-so technique is known as the Valsalva Manoeuvre, or "directed pushing". Left to follow their own impulses, mothers normally wait until the contraction becomes established, then they push ("bear down") between three and five times during each one. Most of these bearing-down efforts are made with some release of air; any breath-holding is brief.

However, most mothers are not "allowed" to follow these spontaneous urges. Unless you are in the care of a midwife or doctor who has decided to make a break with tradition, and what they have been taught to do, you are told to hold your breath as soon as you're aware of the contraction, put your chin on your chest and push for as long and as hard as you can, as if you were constipated. You are not encouraged to "listen" to your body. In fact, directed pushing masks your own instinctive feelings.

Does it matter? It appears so. There are several studies which monitor the effect of directed pushing on the mother and the baby. Research shows that it:

may predispose to abnormalities of the foetal heart rate, slowing it down, because of the way breath-holding leads to a reduction in the amount of blood pumped out of the mother's heart. In some cases, the foetal heart takes a while to recover from this, leading to hypoxia (insufficient oxygen reaching the baby);

may reduce the baby's Apgar score (the assessment - on a a scale of 0 to 10 - of the baby's condition at birth);

may lead to unnecessary tears to the mother's perineum;

may place too much pressure on the vaginal walls and the supportive ligaments of the bladder (because of pushing before the vagina is ready for it), and this may lead to stress incontinence.

As MIDIRS (Midwives Information and Resource Service, which promotes research-based practice) comments: "No scientific evidence supports directed pushing." And assessing some research which compared a "directed" group of mothers with a "spontaneous" group, MIDIRS adds: "This research confirms [directed pushing] as an unnecessary and probably harmful routine intervention on the part of the midwife."

The bible of research-based care, Effective Care in Pregnancy and Childbirth (Oxford) - the tome for assessing what's helpful and unhelpful in maternity care - has put pushing in the "unlikely to be beneficial" category, along with "advice to restrict sexual activity in pregnancy" and "face masks worn during vaginal examinations".

Pat Thomas, whose book Every Woman's Birth Rights (Thorsons) takes a critical look at many childbirth routines, says most women are marshalled into pushing when and how the midwife tells them, and it's an experience they find unpleasant and oppressive.

"Directed pushing is an intrusion," she says. "What are the professionals worried about? The uterus will get the baby out, together with the woman's own powerful urge to bear down."

So why is directed pushing still the norm? Sometimes, it is thought it will reduce the length of labour. But directed pushing has been shown to have only a marginal effect on the length of the second stage - if anything, it may prolong it a little, though the research is still inconclusive. If the second stage is prolonged, there can be risks to a baby who is already compromised - by being small, short of oxygen, one of twins or more, or in a less than ideal position (such as breech).

But concern about the length of the second stage should not apply to the majority of labours. It's usually unimportant for healthy, full-term babies in a head-down position in the uterus, and the approximate size of the baby, and its position, are normally clear by this point of the labour.

Ms Thomas feels the pressure to at least try to speed up the birth process is a result of the way labour is viewed by many health professionals. "Labour is seen as an inconvenient, value-less stage between pregnancy and birth. One mother said she was told to hurry up and get the baby out, as there was someone waiting for the bed."

Directed pushing, campaigners suggest, is also a reflection of the more subtle issue of control. The second stage allows health care professionals an excellent opportunity to step in and actually do something concrete, rather than watching and supporting. Women in the second stage are, after all, not in a position to argue with anyone. Contractions are very strong, they may be coming as often as every two minutes, and they may last a minute and a half each. It's easier to do as you're told.

Jean Davies, midwife and Northern Regional Officer of the Royal College of Midwives, holds that the situation is, nevertheless, changing. "Younger midwives are much more ready to accept that a woman's body can be trusted to do the work, and that directing her pushing can exhaust her," she says.

In her other work as an NCT teacher, Ms Davies aims to teach women how to make their bodies work for them in second stage. "That means learning about positioning, breathing, relaxation, and pushing when it feels right. Mothers can learn to recognise the muscles involved - telling a woman to `push into your bottom', as is so often done, is anatomically close, I suppose, but that's not where the effort should be aimed."

Ms Davies feels the midwife's role is to encourage and to support, and to get the balance right for the individual woman.

Writing in Modern Midwife, midwife Michele d'Entremont presents an overview of research which shows that the drawbacks of directed pushing have been known for 40 years. "We need to re-evaluate our professional practices and beliefs," she says. "We must look beyond tradition and habit as the basis for our practice, and employ only those methods which ensure the safety of those we care for."

Pat Thomas says women should discuss the second stage and how it's managed in pregnancy. "If you want to make sure you do it your way, get it written in your birth plan that you don't want anyone telling you to push, and understand whyn