Cooks River, Earlwood: Disturbing new theory on missing mum and baby - after umbilical cord was dumped on a riverbed

A criminal psychologist has shared his disturbing theory about why a mother gave birth on the banks of a muddy river late last month - as police investigations continue.

A dog walker stumbled across a placenta and an umbilical cord on the banks of the Cooks River in Earlwood, southwest Sydney, about 4.30pm on May 27.

Neither the mother or the baby has been found despite desperate pleas from investigators for her to come forward to ensure both of their safety.

Criminal psychologist, Dr Tim Watson-Munro, said police face an uphill battle in finding the pair.

'If they don't leave a digital footprint, if there's no DNA evidence, they're virtually impossible to track down,' Dr Watson-Munro told Daily Mail Australia.

Dr Watson-Munro theorised the mother could have been facing a myriad of issues that made her disappear with the child. 

'The ones that spring to mind, familiar familial pressure, religious pressure, she may have hidden the pregnancy, it may be a matter of honour to the family,' he said.

'That being said it's a fairly extreme way of doing it because you're by riverbank while you're trying to maintain your anonymity.

'Generally speaking, these sorts of things occur when there's fear, embarrassment, shame or anger,' he said.

'There may be anger directed towards whoever the father may be, there's also on occasions financial pressures.

'To me, it speaks to somebody who's not quite right in terms of their emotions and their cognition.'

The chances of police finding out what happened to the mother and child continues to fall with every day that passes, former homicide detective Charlie Bezzina said.

'The longer it takes for police to find the woman, the more difficult it becomes to make sure they're both alive and well, or tragically dead,' he told Daily Mail Australia.

The ex-detective with Victoria Police said that similar scenarios have occurred because of societal pressures, such as babies being born out of wedlock.

However, he added that the circumstances leading up to the birth couldn't be known without finding the mother.

'One never knows the history or the background as to why a woman would go through a birth and appears to have concealed it,' Mr Bezzina said.

'By then discarding the placenta and the evidence of a person having a baby, it is clear that she's either headed home or headed to a location nearby. But one can only guess.'

The main concern for police would be that she could have 'gone to a different location' outside of the search area and died, according to Mr Bezzina.

He said that an even worse scenario would be that the mother 'may have killed the baby herself and discarded the body'.

'As time goes on, it becomes a lot more difficult, and this may never be solved.'

Leading Sydney Obstetrician Dr Stephen Morris told Daily Mail Australia the mother could be at a higher risk of developing an infection given the place of birth.

Sections of the Cooks River are heavily polluted as a result of traffic congestion, litter, sewage, illegal dumping and industrial and domestic activities.

'Water births are usually just tap water, and you can give birth in the ocean because of salt water, but a river tends to be the worst place to give birth,' Dr Morris said.

'The uterus is a bit of an open wound leaking out the vagina, and so if you get into submerge yourself in that water, it would be more dangerous.

'So if she went for a swim or submerged herself in the body in the river, then that would increase the chance of becoming unwell with an infection in the uterus.'

Dr Morris explained that if the mother becomes infected, she may start feeling feverish, and without medical treatment, this could progress to sepsis.

He added that the extensive police search of the area uncovered nothing that would indicate the baby was harmed at the scene.