Former Sydney athlete Keli Lane has been jailed for 18 years for the murder of her daughter Tegan, 15 years after the baby disappeared.

She was given a non-parole period of 13 years and five months.

Lane has been in custody since December, when she was found guilty of the murder.

About 200 people, including Lane's parents, packed the New South Wales Supreme Court to hear Justice Anthony Whealy sentence the 35-year-old.

Justice Whealy said he accepted Lane had deliberately killed her baby, even though no-one knew how Tegan died.

He said the offence was pre-meditated for a short time and the community does not accept a child being killed by its mother.

But Justice Whealy said Lane presented no risk to the community and was unlikely to reoffend.

He said Lane was only 21 when she murdered her baby and had since undergone rehabilitation.

"The present case may properly be seen, in every sense, as a tragedy involving mother and daughter," he said.

Justice Whealy said there was evidence Lane had a personality disorder but not a psychiatric illness.

He said he agreed with the Crown's description of Lane as a "golden girl" and he said her life had been laid bare by the media.

"She murdered Tegan in a situation of desperation," he said.

"From her perception there was simply no way out."

Justice Whealy said the matter would continue to haunt Lane throughout her life.

Dressed in black, Lane sobbed quietly in the docks before being led away by court officers.

Her solicitor has confirmed an appeal is being prepared against the sentence.

Lane had pleaded not guilty to murdering Tegan shortly after leaving Sydney's Auburn Hospital in September 1996.

The child's body has never been found.

Tegan was Lane's second child. She adopted out her first and third babies.

Lane was also convicted of making false statements under oath in relation to documents dealing with those adoptions.

The former water polo coach and Australian junior representative player has always maintained she gave Tegan to a man she first named as Andrew Morris, then Andrew Norris.

She said she had a brief and secret affair with the man and he was the baby's father.

As recently as a fortnight ago, Lane stated she was innocent of any crime and hoped someone who had information about Tegan or her biological father would come forward.

Lane said she felt like she was being punished for adopting her children out.

"How does the Crown know what a woman thinks or a woman feels when she's in that situation?" she said in a phone call from prison.

Trial

It took a week of deliberations for the Supreme Court jury of six men and six women to reach a verdict in December 2010 after a four-month trial.

The trial followed an inquest and a nationwide police search for Tegan.

There were dramatic scenes in court last year when the jury reached its verdict - Lane screamed and collapsed before an ambulance was called.

She was first questioned about Tegan after John Borovnik, a social worker from the Blue Mountains, west of Sydney, raised concerns with the Department of Community Services after coming into contact with Lane as she was adopting out her third child.

At the end of an inquest in 2006, Coroner John Abernethy described the case as surreal. He also criticised the police delay in questioning Lane.

Lane did not give evidence at that inquest, or at her trial, and she was not charged with Tegan's murder until November 2009.

During the trial, the Crown argued Andrew Norris/Morris was a fictitious person and Lane murdered Tegan because she did not want a child interfering with her ambition to compete for Australia in the 2000 Sydney Olympics.

The missing-person search for Tegan involved police writing to thousands of primary schools with female students, and more than 500 girls were investigated.

During the trial, the jurors were given flow charts to help them keep track of the evidence presented about the police investigation. Police interviews and phone taps were played to them.

Lane's barrister Keith Chapple argued the essence of the murder charge itself was in dispute.

He told the jury there was no proof of how, when or why Lane murdered her newborn child or even that Tegan was dead.

Mr Chapple told the court Lane "took the responsible course" by adopting out two other children.

Secrets and 'lies'

Senior Crown prosecutor Mark Tedeschi told the jury Lane told 95 lies to cover up three secret and unwanted pregnancies so she could preserve her "golden girl" image.

But Mr Chapple argued "there are many things in the case that do not amount to lies at all".

He said Tegan's birth was unremarkable and Lane was not responsible for what other people did not notice.

Mr Chapple spoke of the passage of time involved in the case and said Lane was young when she gave birth to Tegan.

He said adopting out two of her other children was stressful for Lane and an involved process.

The jury was warned by Justice Whealy that only three of the alleged 95 lies Lane had told were relevant to the issue of guilt, while the others could only be used to assess her character.

The judge said to find Lane guilty of murder the jury must be satisfied beyond reasonable doubt she killed the baby.

Witnesses at the trial included Lane's ex-boyfriend, the former rugby league and union player Duncan Gillies, who said they were once very much in love but that he did not know she carried two pregnancies to term during their relationship.

He also admitted to cheating on her when they were together.

Lane's high-profile father is former northern beaches police officer Bob Lane.

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