A sales adviser in his 20s had unprotected sex with his underage girlfriend and impregnated her twice.

The first time she got pregnant, the 15-year-old did not know and found out only when she gave birth to a baby girl at home on Feb 18 last year.

After this, the man was given a conditional warning for having sex with the minor and was ordered to not commit any offences within a year. But he breached this condition and again impregnated the girl, who miscarried their second child in July last year.

The man, 28, was jailed for 1½ years yesterday after pleading guilty earlier this month to two counts of having sex with the underage girl. Two other similar offences involving the same teenager were taken into consideration in sentencing. The couple, who are no longer together, cannot be named due to a gag order.

Deputy Public Prosecutor Kavita Uthrapathy said the couple got to know each other through friends in December 2014 when the girl was just 14. They had sex in his flat in mid-2015 and she gave birth to their daughter in a bathroom of her home the following year.

DPP Kavita said: "The victim's grandmother cut the baby's cord with a pair of scissors and summoned an ambulance... Being only 15 years old when she delivered their daughter, she suffered baby blues and had little knowledge on how to raise a child. By that time, she had quit studying... and obtained a job to try and support her new family."

The girl received treatment at KK Women's and Children's Hospital. As she was a minor, the hospital was obliged to lodge a police report about her case. The court heard she later moved into the flat of the man's family and the couple made plans to get married.

The man was given the one-year conditional warning in lieu of prosecution on May 16 last year and the couple obtained a special marriage licence - though they did not proceed with their plan to marry.

In June last year, they had unprotected sex again and she became pregnant for the second time. The girl miscarried about a month later.

The couple broke up shortly after they discovered this second pregnancy. She moved back to her own home, leaving her daughter behind. The child now lives with her father and paternal grandparents.

The man's lawyer, Ms Sherrie Han, who was assigned to the case under the Criminal Legal Aid Scheme, said the couple are no longer in contact and the man is unaware of his former girlfriend's whereabouts.

For each count of having sex with a minor, he could have been jailed for up to 10 years and fined.