US researchers undertook a study that compared women on a three-step programme, which included injections, with those on a fast-track one.
Women on the three-step plan were first given pills and, if they did not get pregnant, a course of injections. If they failed to get pregnant on the injections, they went on to have IVF.
Meanwhile, those on the two-step programme had pills but, if they failed to get pregnant, they went straight on to IVF.
The study of 503 couples found similar pregnancy rates between the two groups - 78 per cent of women on the fast-track system compared with 75 per cent of women on the three-step system. But the time it took to get pregnant was an average of three months longer for women given injections.
At 11 months after the start of the study, those on injections had taken almost 40 per cent longer to get pregnant.
The jabs were given alongside artificial insemination (also called intrauterine insemination or IUI), to increase the chance of a pregnancy being achieved.
Bill Ledger, professor of obstetrics and gynaecology at the University of Sheffield, said few women in the UK followed the exact three-step US system, but some women did receive injections.
He said the study added to growing evidence that the jabs - which cost £800 to £1,000 per cycle for women going private - may be unnecessary.
"FSH with IUI may become a thing of the past as we become more aware of the risks associated with multiple births," he said.
"If we try to do IVF cheaply and don't waste money doing clever things we can get more babies per investment."
The jabs contain a follicle stimulating hormone (FSH), which increases the number of eggs produced in just one cycle. This also means there is no control over how many eggs are fertilised, increasing the risk of a multiple birth.
Up to a third of women given the injections have a multiple birth. Another side effect is ovarian hyper stimulation syndrome, which occurs in around five per cent of women on the drugs and is potentially fatal.
Mark Hamilton, chairman of the British Fertility Society, said of the research: "This illustrates how important it is for patients to have treatment that is effective, and not to have unnecessary procedures that delay the institution of that effective treatment.
"Patients embarking on assisted reproduction therapy should discuss with their doctors the effectiveness of interventions, and make a judgment on whether to take on treatments with a lower chance of success than IVF."
He said the injections were "something that most clinics will do", in cases of unexplained infertility.
The National Institute for Health and Clinical Excellence (Nice) said it does not recommend the injections for all women.
A spokeswoman said: "We only recommend using FSH drugs with IUI in one circumstance - when women have mild endometriosis."
Richard Reindollar from the Dartmouth-Hitchcock Medical Centre in New Hampshire, presented his findings at the American Society for Reproductive Medicine conference in Washington DC.