While these interventions can be harmful if overused, people working in the private sector have argued they have resulted in better health for babies. Research using a large population-based sample shows this is not so.

Birth interventions include labour being induced, the mother being given an epidural, birth by caesarean section, the use of forceps or a suction cup on the baby's head for delivery, and a surgical cut to the perineum to make the vaginal opening wider.

Such interventions should only be used where there is a medical need. And since they create new risk, women should be told about the benefits and risks of the intervention before it takes place.

In 2012, we published research showing low-risk women having their babies in private hospitals in NSW had much higher rates of obstetric intervention than those giving birth at a public hospital.

Expecting mothers are categorised as low-risk if they are under 35 years of age, have a full-term baby (37 to 42 weeks) with normal birth weight, do not smoke and have no medical or obstetric complications. The latter include high blood pressure, diabetes, a previous caesarean section, twins or breech birth, among other things.

Looking at data from 2000 to 2008, we found only 15 per cent of low-risk first-time mothers in private hospitals had a normal vaginal birth without intervention compared with 35 per cent in public hospitals. Overall, first-time mothers had a 20 per cent lower chance of having a normal birth in private hospitals compared with public hospitals. When we published our findings, privately practising obstetricians defended their intervention rate, recognising it was high, but noting it was worth doing to save babies' lives. This makes perfect sense, but we wanted to know whether there was any evidence for this position.

The result was a paper we have just published in BMJ Open. We looked again at low-risk women giving birth in NSW between 2000 and 2008. This time, we examined problems that required medical attention following birth and re-admission to hospital within 28 days, as well as the rate of intervention at birth. We also looked at stillbirths and infant deaths up to 28 days following birth.

We found babies born in private hospitals were more likely to be born before 40 weeks gestation (as they are more likely to have their labour induced or have an elective caesarean section before 40 weeks) and they were more likely to have some form of resuscitation at birth.

They were also more likely to have a problem following birth and to be readmitted to hospital in their first 28 days for birth trauma, hypoxia (lack of oxygen during birth) jaundice, feeding, sleep or behavioural difficulties, and breathing problems.

All may be associated with higher rates of medical intervention. They also lead to a longer stay in hospital following birth, and separation of mother and child.

There was no difference in the death rates between babies born in the two types of hospitals.

But why had the obstetricians responding to our 2012 report thought their higher rates of intervention had been saving babies' lives?

Part of the reason might be a 2009 paper that concluded better health for babies born in private Australian hospitals. This research had only looked at one data set (we looked at five) and did not control for important risk factors, such as low birth weight, which can lead to more deaths and medical problems in the baby.

And there is an even bigger problem with wider ramifications. A recent Queensland study showed a significant number of pregnant women are not consulted in decision-making about the medical procedures they undergo, or informed of their risks and benefits.

This can lead to trauma and disempowerment and can affect how mothers connect with their newborn babies. Some women are so traumatised, they become depressed and even develop post-traumatic stress disorder.

Women about to give birth should question interventions to assess whether they are necessary. For those with low-risk healthy pregnancies, private obstetric care in a private hospital, with higher rates of intervention, may lead to avoidable problems for babies.

Hannah Dahlen is professor of midwifery at the University of Western Sydney. Sally Tracy is professor of midwifery at the University of Sydney. This article ran on The Conversation