After childbirth, some new mothers wishing to avoid another pregnancy ask their doctors to provide reversible contraception, like an intrauterine device. But normally, new mothers are told to return for contraception six weeks after giving birth, after fully half of them have already resumed sexual relations.

A study, published in Obstetrics and Gynecology, suggests that this practice should change. Women who received IUDs during cesarean sections were far more likely to be using them six months later than women who were told to return to the doctor’s office to receive one.

The authors concluded that altering the practice could help reduce unintended pregnancies and the number of babies conceived within 18 months after a previous birth, thus mitigating a number of infantile risks, including prematurity.

“We are meeting a woman’s needs better when they get their contraception at the time of delivery,” said Dr. Lisa M. Goldthwaite, an author of an editorial accompanying the new study and a family planning fellow at the University of Colorado School of Medicine. “You can’t continue to use an IUD you never got.”

The study was a randomized trial of 112 women giving birth at North Carolina Women’s Hospital in Chapel Hill who wanted an IUD. Eighty-three percent of women whose IUDs were placed during their C-sections were still using them six months postpartum, compared with just 64 percent of women who had planned to get IUDs at a separate office visit.

Participants received free IUDs and were paid nominally for visits. Still, a quarter of women assigned to get an IUD at six weeks never showed up.

The months following childbirth are “an intense, busy, hard time for most women,” said Dr. Erika E. Levi, the study’s lead author and an assistant professor of obstetrics and gynecology at Albert Einstein College of Medicine in the Bronx.

“We need to make it easier for women to get access to the kind of contraception they want as new mothers.”

Research on postpartum IUDs has mostly focused on those implanted after vaginal births, not C-sections. Women don’t necessarily realize “this can be done at the time of a C-section,” said Dr. Erika Werner, an assistant professor of obstetrics and gynecology at the Warren Alpert Medical School at Brown University.

A study published in the journal Fertility and Sterility recently found in-hospital insertion of an IUD prevented an estimated 88 unintended pregnancies per 1,000 women over a two-year period, compared to routine placement between six to eight weeks.

A 2010 review of nine randomized trials by the Cochrane Database of Systematic Reviews found that immediate insertion of an IUD after both vaginal and cesarean deliveries appears to be safe and effective. But a higher percentage of those IUDs are expelled, compared with those placed later.

That held true in the new trial, too. Eight percent of women who got IUDs in the hospital during their cesareans lost the devices, compared with only 2 percent of women who got an IUD later. Nevertheless, nearly 20 percent more of the in-hospital group still had IUDs at six months.

Expulsion is a problem if it goes unnoticed, because then a woman mistakenly thinks she is using birth control. But, “expulsion in and of itself isn’t a big deal,” Goldthwaite said.

Levi and her colleagues urged physicians who have long hesitated to offer immediate implantation of IUDs to reconsider.

Yet the biggest barrier to getting an IUD just after delivery remains a lack of reimbursement. Delivery costs are bundled in a package, so hospitals are not paid for implanting an IUD, which can range from $625 to $900.

In the past few years, at least 12 states have changed their Medicaid policies to allow hospitals and physicians to be reimbursed separately for in-hospital IUDs. Most private insurers have yet to follow suit.