Cooks River, Earlwood: Major update in urgent effort for baby delivered along Sydney reiverbank

Fears remain for the safety of a mother and her newborn baby nearly seven days after a placenta and umbilical cord were found on a Sydney riverbank.

Investigators are yet to track down the woman or the child nearly three days after a dog walker found a placenta and umbilical cord on the banks of the Cooks River at Earlwood.

Testing of the material revealed the placenta and cord belonged to a baby boy, police said on Thursday.

Authorities have held fears for the safety of the mother and newborn since it was found on Monday afternoon.

The mother is being urged to seek medical attention at a nearby hospital as police insist the health of her and her son remains their top priority.

Leading Sydney Obstetrician Dr Stephen Morris told Daily Mail Australia that there is a risk of the mother developing an infection ten days after giving birth due to the unsanitary conditions of the river.

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 lack of excessive blood would most likely mean there were no complications during the birth.

'It doesn't sound like she was haemorrhaging as there wasn't excessive blood in the area, and she hasn't turned up to hospital unwell unless she's deceased,' Dr Morris said.

'In terms of the baby, he has the mother's breast milk, which should be fine, assuming he doesn't get too cold,' Dr Morris said.

A full-scale search of the area on Tuesday did not show any evidence the baby had been harmed, nor did it reveal any immediate clues to why the placenta and umbilical cord had been left there.

Police divers and a blood detection dog were called in before the search wrapped up later that afternoon.

Tony Robson, who made the initial discovery, said the placenta and umbilical cord were not hidden but simply placed on top of the riverbank.

'It's a secluded dead-end spot … the (dogs) were off-lead having a bit of a romp around and (one dog) jumped down into the mangroves and spotted something,' he told Seven News.

'(It was) low tide so it was just sitting on top of the mud, the water was quite a distance away … I've seen three births, you know what you're looking at.'

On Tuesday, police identified a potential burial site near the riverbank.

But it turned out to be a false alarm, instead discovering a cat that had been recently buried.

Investigators have suggested the woman might have disposed of the placenta and umbilical cord at the river because she did not want anyone to know about the baby.

'Childbirth, for many people, can be a traumatic time, and it can be very distressing … I am deeply concerned for the safety and the mental health of the mother,' Superintendent Christine McDonald said previously.

'There is no judgment, they need to know we are concerned for them.'

The placenta and umbilical cord were found not far from a sports field and Islamic centre on Lang Rd, close to a busy footbridge frequented by walkers, joggers and cyclists.

The Cooks River flows from Yagoona in Sydney's outer southwest and runs into Botany Bay at Kyeemagh, 23km away.