In a study that tracked couples trying to conceive, researchers found no differences in the success rates of those who used over-the-counter lubricant products and those who didn't.

Past research has shown that lubricants can impede sperm's ability to swim, and even damage their chromosomes, at least inside a test tube.

"There are some recommendations that couples trying to conceive should not use lubricants, for fears that it will be toxic to sperm and make it harder for them to get pregnant," said Dr. Anne Steiner at the University of North Carolina at Chapel Hill, who led the new study.

Researchers cautioned couples against changing their behavior based on the results of this one new study, though.

"It's important that the research is repeated. We're kind of the first people to look at this, so we have to take the bigger picture into context," Steiner told Reuters Health.

It's estimated that 62 percent of women in the U.S. have used a vaginal lubricant during intercourse, and some 25 percent of women use lubricants regularly.

There's also evidence that couples trying to conceive are more likely to need lubricants, to ease problems like vaginal dryness, and about a quarter of all couples who are trying to get pregnant will use the products.

So Steiner and her team set out to test whether lubricant use was really linked to fertility problems. And if so, whether the lubricants were actually to blame, or using them might be just a sign of other issues, like a lack of natural vaginal mucus, that could affect fertility.

The researchers made use of information collected between 2008 and 2010 through the University of North Carolina's 'Time to Conceive' study, which looks at factors affecting fertility in women aged 30 to 44.

A total of 175 women, all in the early stages of trying to get pregnant when they entered the study, were included in the analysis. For six months, or less if they conceived, the women kept a record of each time they had intercourse and if they used lubricant.

Women were classified as frequent users if they used lubricants at least 50 percent of the time when they had intercourse, and occasional users if they used them less often.

According to the findings reported in Obstetrics and Gynecology, women who frequently used vaginal lubricants - about 14 percent of women in the study - were just as likely to get pregnant as those who never used lubricants.

Overall, about 63 percent of the women included in the analysis got pregnant during the six-month study.

Among these, 73 percent of lubricant users conceived by their sixth cycle of trying and 68 percent of non-users conceived.

Steiner's team also checked the effect of lubricant use specifically during the women's most fertile time of the month, a few days either side of ovulation.

Again, they found no differences. Women who used lubricants during their most fertile days of the month got pregnant at the same rate as those who didn't use lubricants - however, even lubricant users were having sex without the help of lubricants around 75 percent of the time, on average.

When Steiner's team looked at results of testing for adequate cervical mucus, they found no link between low mucus and lubricant use.

In their report, the researchers speculate on several possible explanations for their findings. One is that lubricants might not reach into the upper vagina where sperm are deposited. Another is that sperm might move quickly into the cervix, avoiding exposure to the lubricants. Or, lubricants might promote fertility by enabling more frequent intercourse.

Steiner emphasizes that the study does have limitations and further research is needed to confirm the findings.

Dr. Agarwal Ashok, a researcher who has looked at the effect of lubricants on sperm at the Cleveland Clinic in Ohio, also urged caution.

Ashok has found that most of the commercial lubricant brands in the U.S., including FemGlide, Replens and Astroglide, harmed sperm in a test tube, with the exception of Pre-Seed, a product with a pH more like the human body. (See Reuters Health story of March 11, 2008).

"Most reproductive physiologists suggest that while trying to conceive, couples should do all they can to optimize sperm function and fertility. Choosing a lubricant that has been shown to not harm sperm on direct challenge contact in laboratory studies would seem prudent," Ashok told Reuters Health in an email.

The new study doesn't address whether lubricants may harm fertility in the long-term.

"It's reassuring for couples who basically feel they need to use a vaginal lubricant if they are trying to have regular intercourse while they are trying to get pregnant. If a couple is having issues with vaginal dryness and needs to use a lubricant, they can be somewhat reassured by these findings," Steiner said.