A high-profile obstetrician and gynaecologist who is also a professor with the University of Sydney made remarks to peers attending a medico-legal conference in Melbourne that were so sexist and condescending that some attendees were in tears and conference organisers vowed never to invite him back.

Prof Hans Peter Dietz, an internationally renowned pelvic floor expert, has been the subject of numerous complaints to his employers, the Nepean hospital and the University of Sydney.

Numerous women, including midwives and professors, have separately expressed serious concerns about Dietz’s behaviour.

Three health professionals who spoke to Guardian Australia said Dietz told attendees at medical conferences that women should be forced to sign a consent form if they wanted to give birth vaginally, to confirm that they were aware of the risk that their bodies might be left with tears and other complications if they did not get a caesarean instead.

‘Midwives are incompetent’

The director of midwifery studies at the University of Technology Sydney, Dr Christine Catling, attended the Annual Obstetric Malpractice Conference in Melbourne in August 2018 and was asked to speak about midwifery continuity of care and the management of large babies.

While on a panel, Catling spoke of the importance of not scaring women if there were concerns about vaginal delivery and to instead discuss different options and risks. Dietz stood up and interrupted her. “He declared that it was his job to scare the bejesus out of women,” Catling said.

She said Dietz then said that the practice where he previously worked in New Zealand had changed policies since he left, which meant around 50% of women were now seen by midwives rather than obstetricians, a change he said would affect the quality of documentation.

“I grabbed the microphone and said that there was no reason that the documentation would be affected as the midwives are competent at their jobs,” Catling said. “It was then that he stated that midwives are incompetent.”

The conference organiser apologised profusely to Catling during the break.

“The next day I found the conference organiser in tears in the bathroom after she had asked him to pay some respect to the speakers,” Catling said. In a subsequent email between the event organiser and Catling, seen by Guardian Australia, the organiser said she had been involved in the conference since its inception.

“I have never encountered a delegate/speaker who is so extreme in their views and was not aware of this prior to the event,” she wrote to Catling. “I will not be including him in any of my events moving forward. There is no place for aggression and disrespect at our events.”

Prof Hannah Dahlen, who in June was made a member of the Order of Australia for her research in midwifery, said Dietz refused to use her “professor” title and had criticised her work publicly at conferences.

“I met Dietz in early 2000 and went to him with my PhD idea to do a large randomised controlled trial on the application of warm compresses to a woman’s perineum during the late second stage of labour to see if it reduced tearing and increased comfort for women,” Dahlen said.

“He told me it was rubbish and not science and I would be laughed out of town for such a stupid idea.”

Dahlen went on to do the world’s largest randomised control trial on warm compresses during late-stage labour, which is now recommended practice and the only treatment proven to make a moderate difference to comfort during late-stage labour. The evidence is used in guidelines around the world.

“I then debated him at a medical conference and realised how angry he was with midwives as he screamed at me, and it was clearly personal,” Dahlen said.

Bashi Hazard, a lawyer and the director of Human Rights in Childbirth, said she was invited by the Australian and New Zealand Journal of Obstetrics & Gynaecology to contribute a piece about Dietz’s stance that all women should sign a form saying they understood the dangers of vaginal birth before choosing to give birth that way.

“My legal argument was how can women consent to what is a natural bodily function they can’t control?” she said. “You can’t force women to do that.”

Hazard said she sent the article to some lawyer peers and consumers for their feedback before sending it to the journal for review and publication. She was shocked to receive a response from the journal accusing her of breaching their guidelines by disseminating the article widely ahead of publication.

“I found out one of the people I consulted with on the article took the article without telling me and gave it to Dietz, which would have been fine,” Hazard said. But he then forwarded it to other people, she said, which had led to the journal’s response.

Hazard was so rattled by the potential ramifications to her professional reputation that she went to the police. She also complained to the University of Sydney, Dietz’s employer. In response the university said Hazard had not provided it with enough evidence to take the complaint further.

The university declined to answer specific questions from Guardian Australia, but said it was “aware of certain complaints” about Dietz and was “making inquiries as a matter of priority”.

“We are unable to make further comment while the process is ongoing,” a spokeswoman said.

“While our academics are entitled to express their own opinions, and would defend their right to do so, we consider recently reported statements from Dr Dietz to be unacceptable and in conflict with the university’s own position, policies and practices. We are absolutely committed to our ongoing work to achieve a positive workplace culture and gender equity in Stem, including medicine and health.”

A Nepean Blue Mountains local health district spokesman did not answer questions from Guardian Australia about the number of complaints received about Dietz or whether they supported his comments at medical conferences.

“Almost 74% of our staff are female,” the spokesman said. “They are valued members of our clinical and professional teams.”

‘Offensive language’

SBS news first reported that Dietz sent an email to committee members of the NSW medical union stating the workforce was “increasingly vulnerable because it’s increasingly female and not exactly prepared for adversity because school and uni are ‘safe spaces’ [sic].”

“Suicides are one result,” he wrote. “Inability to cope with everyday nastiness is another.”

Further reports have since emerged.

Dr Aimee Sing, a consumer advocate with Homebirth Access, complained to numerous bodies about Dietz after he had a letter published in a Blue Mountains local newspaper accusing her of taking a 1:100 risk of her or her baby dying by choosing to have a home birth for her second child, given she had a caesarean for her first.

Peer-reviewed journal articles report that women with a prior caesarean scar are at some risk of uterine rupture, but a much lower risk than that described by Dietz. .

Midwife Oceane Campbell also told Guardian Australia she had been disrespected by Dietz, this time at a medical seminar in Newcastle in 2017 where he was a guest speaker. She said she was “really shocked about the offensive language he used around women’s bodies and birthing”.

“He was referring to different perineal tears and showing diagrams of tears, and he referred to one third-degree tear as a ‘bomb site’.”

When Dietz showed attendees a graph detailing tear rates following vaginal birth, Campbell asked a question, which she said prompted Dietz to begin shouting at her.

“I said my understanding is the weight of the pregnancy on the pelvic floor increases the risk of incontinence after a certain number of pregnancies, [and] this is the case whether you have a caesarean or vaginal birth,” Campbell said.

“He snapped at me. He looked angry … he [was] nearly frothing at the mouth. He was red-faced and was so hostile and he said ‘you don’t know what you’re talking about’. He called my intelligence and profession as a midwife into question. In the end the host had to ask him to stop.”

A midwife who attended an obstetrics conference in Sweden that Dietz also attended told a similar story of Dietz’s attitude. “The thing that startled me most and upset the doctors as well was that he said that it was not good to be a female obstetrician working with female midwives,” she said.

“He said this would lead to a competition between the two professions as they both want to care for the woman in labour. It was so strange that he said this with an audience of almost only women gynaecologists and obstetricians. And in Sweden where almost all women call themselves feminists, where we try really hard to collaborate.”

While women who have risk factors such as overweight, diabetes and previous caesareans are at higher risk of complications and therefore are not recommended to pursue home-births, there is increasing evidence that healthy, low-risk women with no risk-factors are receiving too many interventions such as cesarean and forceps. There is debate between health professionals as to whether these healthy women can be as safe receiving midwife-led care or by giving birth at home.

The president of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, Dr Vijay Roach, criticised Dietz’s comments.

“RANZCOG unequivocally refutes the recent comments made by Prof Dietz,” he said. “The workplace only benefits from the full and equitable participation of women, and any vulnerabilities requires attention to underlying systemic inequities. Prof Dietz’s language has no place in the speciality of obstetrics and gynaecology or medicine more broadly.”

Dietz did not respond to requests for comment.

• After the publication of this article Prof Dietz told the Sydney Morning Herald that he considered a number of the accusations in this article to be defamatory and others nonsensical: “Several of the allegations, some dating back almost 20 years, are patently untrue and have already been rejected by the bodies involved,” he said. “I consider this a form of public bullying intended to silence criticism of natural childbirth ideology and activism”.

• Do you know more? melissa.davey@theguardian.com

• This article was amended on 8 November 2019 to clarify claims around the risk of vaginal delivery for a second birth after having had a caesarean.