ELAINE O'Hara told her sister the year before she disappeared that she had a miscarriage, the jury in the trial of Graham Dwyer has heard.
Her sister, Anne Charles, said in evidence that Ms O'Hara told her this in 2011, and that she miscarried after a one-night stand.
Her father's partner, Sheila Hawkins, said Ms O'Hara had also told her about a miscarriage that year, as well as having had sex for the first time.
Both women gave evidence on the third day of the trial of Mr Dwyer at the Central Criminal Court.
Mr Dwyer (42), an architect of Kerrymount Close, Foxrock, is pleading not guilty to the murder of Ms O'Hara (36), a childcare assistant, at Killakee, Rathfarnham, on August 22, 2012.
Ms O'Hara, from Killiney, was last seen alive near Shanganagh Cemetery in Shankill.
Her remains were found by a dog walker in undergrowth in the Dublin mountains on September 13, 2013, more than a year after she disappeared.
Ms Hawkins, a psychologist, told the jury she lived at an apartment in Stepaside which was in full view of Ms O'Hara's.
She offered Ms O'Hara a lift for the morning of August 23, when she was due to go to the Tall Ships Festival.
Ms O'Hara texted beforehand to say she would accept the lift.
Ms Hawkins had been speaking to Mr O'Hara after he said goodbye to his daughter the day before and he had been "delighted about" how he had found her to be.
At the end of the evening of August 22, Ms Hawkins became "niggly concerned" when she saw no activity at Ms O'Hara's home.
She believed she had gone to bed early in preparation for the following day, and sent Ms O'Hara a text saying: "See you 7.15am."
She was to pick her up the following morning at a bus stop in the area but Ms O'Hara was not there. She drove to her apartment and tried the bell but there was no answer and she left a message on her phone.
No lights came on at the apartment by 7pm that evening and she thought maybe Ms O'Hara had stayed on late at the Tall Ships
She checked the underground car park at Belarmine Plaza and Ms O'Hara's car was not there.
In cross-examination by Remy Farrell, for the defence, Ms Hawkins said she had a conversation with Ms O'Hara in 2011 in which Ms O'Hara said she had sex for the first time and that she had a miscarriage.
She described Ms O'Hara as a very conflicted girl and placed her emotional development at around the age of 15.
She believed what Ms O'Hara told her was credible because she did not think she was creative enough to tell blatant lies but would embellish within her own frame of reference.
Asked if Ms O'Hara told her she had an interest in S&M - sadism and masochism - Ms Hakwins said: "No, she said she had an interest in tying herself up in her adolescent years.
"There were two blurting outs, one that she had had sex for the first time and the other that she had a miscarriage."
She knew about Ms O'Hara self-harming and described an incident when she was shopping for clothes for a Christening in Dundrum Town Centre.
Ms O'Hara called her into the changing room for her opinion and Ms Hawkins noticed two marks on her leg, like "bramble scratches" but symmetrical, and three to four inches long.
"I knew they weren't accidental and she said she had cut herself again," she said.
Ms Hawkins told the court that she had found a "black latex suit consistent with S&M" in Ms O'Hara's apartment in a search when she went missing.
She said that after Ms O'Hara disappeared, she and Ms O'Hara's father had searched her apartment.
She put her hand into a wicker basket and "recoiled", she said. "I recoiled because my hand felt this oily, rubbery substance," she said. Pulling it out, she saw what looked like black latex.
Ms Charles told the jury her sister, Ms O'Hara, had phoned her in November 2011 and told her she had a miscarriage in May.
She claimed she had become pregnant as a result of a one-night stand.
Ms Charles said she had asked her sister how far along she was and who the father was but that "she fudged my questions".
Ms Charles described her sister - who was younger by two years - as a "naive" person who would "tell a man on the street her life story".
They had been close as children but not particularly close as adults, she said.
Ms O'Hara's psychological difficulties meant that she "acted quite young", she said.
"She never really grew up as much as the rest of us," Ms Charles said.
"She was very naive, very trusting of people."
When Mr O'Hara became concerned about his daughter on August 24, 2012, Ms Charles' husband checked the cemetery and found her car parked nearby.
The trial continues before Mr Justice Tony Hunt and a jury of seven men and five women.