A 30-year-old woman accused of attempted murder following the discovery of a baby boy in a drain in Sydney's west will remain behind bars until her next court appearance.

Saifale Nai did not appear for the brief hearing at Blacktown Local Court on Monday.

The court heard she will appear at Penrith Local Court on Friday.

No application for bail was made and it was formally refused.

Despite earlier estimates that the boy was two to three days old, police later said that he is seven days old and ha been placed in the Quakers Hill drain on Tuesday, 24 hours after being born.

If the allegation is true, it means he survived in the drain for five days before being found by a passing cyclist on Sunday morning.

The baby is now in a stable condition at Westmead Children's Hospital.

Police suspect the baby was squeezed through the stormwater drain's narrow opening and dropped about 2.4 metres.

After he was heard screaming on Sunday, several people lifted the heavy slab covering the drain to get him out.

The baby is now in the care of the NSW Family and Community Services (FACS) Minister.

It will be up to the state agency to assess what now happens to him.

The baby was discovered, wrapped in a striped hospital blanket, down the drain on the side of a bike track along the M7 motorway just after 7.30am.

Police doubt he would have survived Sunday's 40 degree-heat.

'It was already undernourished, and dehydration would have taken affect, so we would have had grave fears for the child's welfare had it been exposed to this weather for the rest of the day,' Inspector David Lagats said.

Cyclist David Otte, out riding with his daughter, said he was meant to find the little boy.

'We were meant to be there I think,' Mr Otte, from Rydalmere, said on Monday.

'We're not heroes or anything. We would have done it for anybody but we were just glad that we were there,' he told Melbourne radio 3AW.

Mr Otte said two men who had heard a strange noise coming from a drain about 150 metres from Quakers Road had flagged him down.

'It's a pretty unmistakable cry when you hear a baby crying.'