Darren Heath, 45, from Taynton, was sentenced to three years and nine months after pleading guilty to five counts of misconduct in public office.
Bristol Crown Court had heard how Heath got one of his victims pregnant and convinced her to have an abortion.
Gloucestershire Police believe there may be more victims.
In sentencing, Judge Neil Ford QC described Heath's behaviour as "corrosive to the reputation of the police service generally".
The force said Heath used his position to identify women - "often victims of crime who were already extremely vulnerable" - whom he could offend against.
He was described as "manipulative and calculating" by the force, which suspended him last year following an investigation into a complaint made against him in 2012.
The offences took place between 2002 and 2012.
Previously, Bristol Crown Court had heard that Heath was first warned about his behaviour in 1996 - a year after joining Gloucestershire Police - following a complaint by a student.
He had asked her if she "fancied a bit of fun".
"She subsequently made a complaint which was dealt with by Pc Heath being given advice."
Heath met his first victim in 2002 after she was arrested for drinking and driving.
Six years later he met another victim who approached him in a police car after a man fell unconscious in the street.
He later visited her home where the pair had sex and then persisted with visits - up to four times a week - before the woman fell pregnant with twins.
Heath, who has two children of his own, then convinced her to have a termination.
He met another victim after arranging a restorative justice programme for her son.
The woman ended the relationship after realising Heath was "only interested in a sexual relationship", the court heard.
A "manipulative and calculating" police officer who abused his position to have sex with vulnerable women he met while on duty has been jailed.