Samantha Orobator, 20, was convicted of drug trafficking and sentenced after a three-hour trial, an official in the southeast Asian country said. He declined to give his name because he is not authorized to talk to foreign media.
Orobator's mother was in the courtroom, he said.
The British Foreign Office also confirmed Orobator's sentence.
She was jailed last August at the airport in the Lao capital, Vientiane, and charged with carrying about half a kilogram of heroin.
London and Vientiane signed a prisoner transfer agreement last month, the Foreign Office said.
But it does not kick in automatically at this point, a Foreign Office representative told CNN Wednesday.
"Before transfer can take place, the sentence must be final with no appeals or legal processes outstanding," the representative said, declining to be named in line with policy.
"Both states and the prisoner have to consent to a transfer. We are seeking access to Samantha" and will ask her "how she wants to proceed."
Orobator is more than five months pregnant, and enters her third trimester on Saturday.
The circumstances under which she became pregnant in prison remain unclear.
She told her mother she was not raped in prison and that the father is not a Lao prison official.
A newspaper run by the Lao government reported Orobator as saying she impregnated herself with the sperm of another prisoner being held in the same jail.