Former Australian water polo champion Keli Lane has been jailed for at least 13 years and five months for murdering her newborn baby Tegan more than 14 years ago.

In the NSW Supreme Court today, Justice Anthony Whealy set a maximum term of 18 years.

The 35-year-old former athlete was found guilty last December of murdering her second baby, Tegan, on September 14, 1996, after they left a Sydney hospital and before she went to a wedding.

Lane, who had two terminations as a teenager, kept three pregnancies and births secret.

She adopted out her first and third babies, but was convicted of murdering Tegan, whose body has never been found.

Lane claimed she handed Tegan over to the infant's father, a man with whom she said she had a brief and secret affair.

But the crown contended she murdered the baby a she had not wanted to be burdened with a child as she wanted to pursue her sporting, sex and social life.

Lane, whose previously dyed blonde hair is now dark brown, showed no reaction as the judge handed down his sentence.

Agreeing with the crown description of Lane as a "golden girl", Justice Whealy said she had murdered Tegan "in a situation of desperation".

"From her perception, there was simply no way out," he told the packed court room, which is the largest in the complex.

The judge concluded that Lane was fully rehabilitated and presented no danger to the community.

He said the two aggravating features of the murder were the age of the victim and that it had been an abuse of a position of trust.

"The life that has been taken is a baby, completely defenceless," he said.

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

He noted the tragic fact that, for whatever reason, Lane could not tell her own mother of the secret birth of her three children.

"Secondly, it is a tragedy between mother and daughter in the sense that the offender disposed of her second child Tegan, and in so doing, tore asunder the natural relationship between mother and daughter.

"That fact has, and will, continue to haunt throughout her life."