For in vitro fertilization, extra follicle-stimulating hormone, or FSH, is used to trigger the ovaries to grow and release multiple eggs, which are then fertilized outside the body and re-implanted in the uterus.

In an analysis of four past studies including over 2,300 women with infertility, researchers found the women were just as likely to get pregnant -- and didn't have any more complications -- when they got a single, long-acting dose of FSH rather than daily shots.

"Long-acting FSH (weekly injection) is a good and safe alternative to daily injections in the first week of ovarian stimulation for IVF," Dr. Jan Kremer from Radboud University Nijmegen Medical Center in the Netherlands, who worked on the review, told Reuters Health in an email.

However, he said there is still limited data on how the weekly hormone shots work in certain groups of women, including older women with less of an ovarian response and those with fertility problems because of polycystic ovary syndrome, whose ovaries might over-respond.

The long-acting shot is used in Europe but not currently available in the United States, because it hasn't been approved by the Food and Drug Administration.

The new findings are published in The Cochrane Library and include all high-quality data Kremer and his colleagues could find on the shots.

Out of 2,335 women included in the analysis, 987 got usual daily FSH shots for a week and 1,348 had one long-acting shot at a range of doses, along with the usual course of other IVF hormone injections.

In studies that used the lowest dose of the long-acting hormone -- between 60 and 120 micrograms -- fewer women in the one-shot group got pregnant than in the daily FSH comparison group.

However, at slightly higher doses (150 to 180 micrograms), pregnancy and birth rates didn't suffer: 343 out of every 1,000 women getting one long-acting shot had a baby, compared to 336 out of 1,000 in the daily-shot group.

And the long-acting shot didn't seem to come with a higher risk of miscarriage, having twins or developing a pregnancy-related complication, including swollen ovaries.

IVF typically runs for about $15,000 a cycle. Kremer said the cost of the two types of injections is "more or less comparable."

Dr. Samuel Pang, medical director at the Reproductive Science Center of New England in Lexington, Massachusetts, said the main advantage of the single shot is convenience. FSH shots are simple injections that women can give themselves, similar to insulin, he said, but the process can still be a hassle for some.

"In my mind, based on the studies that have been done and based on my own experience, it is a safe and effective product," Pang, who wasn't involved in the new review, told Reuters Health.

"The only caveat is it really needs to be used in well-selected patients."

Like Kremer, he cautioned against using the long-acting shot in women who are unlikely to respond to the hormone -- or those who may over-respond.

A week after getting the long-acting shot, many women still need a few daily injections of FSH before they're ready to have their eggs harvested, he added.

Pang worked on research that has been submitted to the FDA on the hormone shot, but says it's at least a year or two away from being available in the U.S.

"At this point in time, while it's very promising based on the studies that have been done and the experience in Europe, it's not anywhere near market here."

So-called post-marketing studies in Europe and Australia continue to suggest the drug is safe and works well, according to Dr. Arthur Leader, from the University of Ottawa and Ottawa Fertility Centre who also didn't participate in the review.

"It simplifies the whole process, makes it easier for the woman while not compromising her health or the health of the children that are born," he told Reuters Health.

SOURCE: bit.ly/LFupNY The Cochrane Library, online June 13, 2012.

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