A pregnant mum whose baby was due on Christmas Eve collapsed and died in front of friends at a coffee morning.
Paramedics tried to save Amy Wilson, 31, and her unborn son, Harry, but she died later in hospital on November 16.
Her partner Peter Reid is now caring for their two daughters, Halle, seven, and Chloe, two, in Laurencekirk, Aberdeenshire.
He has been told by doctors that Amy may have suffered from a heart condition so rare there are no tests yet to detect it.
He said: "I was told they are struggling to find the cause of death.
"She was looked after as well as she could have been and had the care she needed while in hospital.
"Not only do I want to know what happened but the doctors also want to know.
"It could be that Amy had one of these rare heart conditions that they don't know of yet and may not be tested for another 10 years.
"Everything appeared to be normal and it could be that there is no test yet that will give us the answers."
Amy and Harry were laid to rest in a joint funeral. An investigation by NHS Grampian is ongoing after Amy had spent time in the maternity unit at Aberdeen Royal Infirmary (ARI) in the lead-up to her death.
She had previously suffered a bout of extreme sickness and spent the first week of November at the hospital until being released 10 days before she died.
Tests are ongoing to determine what condition she suffered from.
Peter said: "I don't mind if I find out one week down the line, two weeks down the line, but the truth is I may never know.
"The doctors are struggling and I dare say I am going to struggle if I don't get the answers that I need."
A spokeswoman for NHS Grampian said: "Senior staff from Aberdeen Maternity Hospital met with Mr Reid. "
Our duty to maintain patient confidentiality means we cannot comment further.
"Our thoughts remain with Mr Reid and his family at this difficult time."