But the estate agent was left unattended for 45 minutes and was discovered only when the friend returned from picking up her belongings, an inquest in Nottingham heard.
Coroner Dr Nigel Chapman said he was able only to record an open verdict because of uncertainty over how Mrs Maddi died."
But when he came back an hour later Mrs Maddi was still in the bathroom with the door locked.
She did not respond to knocking so midwives opened the door and found her submerged under water and not breathing.
Doctors resuscitated her and delivered her baby Jayden but Mrs Maddi later died.
Hospital officials have since admitted there were no official guidelines on whether pregnant women should be left to bathe on their own - but there was the assumption among the midwives on duty that Mrs Maddi would not be left alone during her bath.
The hearing was told Mrs Maddi had written to the hospital saying she was under stress because her mother had died and had warned them the fainting attacks were increasing.
Hospital management have promised to introduce guidelines about the supervision of patients to avoid a repeat of the tragedy.
Mr Maddi, 29, a warehouse worker, has instructed solicitors to take legal action against the hospital trust.
He said after the hearing: "I hope they keep to their word and make the changes, that is all I want now. My son will never know his mother.
"My son might not even have been alive if Paul hadn't come back when he did. I just hope that something-good will come out of losing my wife."
Mr Guthrie added: "The word observation means to watch but obviously Lorraine wasn't watched.
In other words, no one was "with" this mother in labour.
