You've found out you're pregnant, so you're taking a daily prenatal multivitamin/mineral pill to ensure your unborn baby's health. You know, in particular, that it's important for the fetus to get folate, a B vitamin in the pill, since that nutrient has been found to dramatically cut the risk of debilitating and sometimes life-threatening neural tube defects. But what if the folate in the pill doesn't dissolve, which means you have little chance of absorbing it into your system and passing it on to the baby through the placenta?

It's not a far-fetched scenario. When University of Maryland researchers tested nine prenatal multivitamin pills a couple of years ago, six of them failed the dissolution test for folate set up by the Rockville-based U.S. Pharmacopeial Convention (USP), an independent, not-for-profit group of pharmacologic and medical experts that sets quality standards for drugs as well as supplements.

According to USP, 75 percent of the folate should dissolve within an hour. Two of the products failed so miserably that less than 25 percent of the amounts listed on labels dissolved.

It's not just prenatal vitamins that have been found to have problems. Shortly after the University of Maryland researchers published their findings, the Tufts University Health & Nutrition Letter reported that a couple of multivitamin/mineral supplements for nonpregnant adults failed to meet USP dissolution standards. One was GNC's Women's Solotron--only 27 percent of the B vitamin riboflavin dissolved. The other was Geritol Complete--68 percent of the riboflavin in the pills dissolved.

Previous work at the Tufts Letter had found that TwinLab Calcium Citrate Caps supplements as well as calcium supplements from at least one other company also failed to meet established dissolution standards.

Given that millions of Americans now take nutrition supplements to the tune of billions of dollars a year, it's potentially a huge problem. It's also an unregulated one. Supplements are treated by federal legislation as foods, not drugs, so if a nutrient pill doesn't dissolve according to USP standards, there's nothing the government can do about it. That is, it's perfectly legal for a company to sell a vitamin/mineral pill that passes right through the gastrointestinal tract essentially intact.

Some in the supplement industry have argued that the problem is exaggerated, maintaining that the USP tests for dissolution are not applicable. The makers of GNC's Women's Solotron, for instance, say that the dissolution standard "is more appropriate for" various pharmaceutical products than for supplements. Other companies say that the dissolution tests are irrelevant because they are conducted in test tubes, or in vitro, rather than in the human body, or in vivo. Such tests, manufacturers believe, are not good indicators of whether the nutrients dissolve in the gut.

But V. Srini Srinivasan, director of the Dietary Supplements Division at the USP, disagrees. "In vitro does count," he says. "The correlation" between in vitro and in vivo dissolution "has been proven in the case of drugs" and is there for supplements, too. "It is not exact," he concedes, but it is a measure of what a product can do in the body.

The argument has placed the spotlight on supplement standards, which has goaded manufacturers to begin reformulating. "I think [the situation] is improved," says Stephen Hoag, an assistant professor of pharmaceutical sciences at the University of Maryland, who led the study on prenatal vitamins. "I have talked to various manufacturers . . . . [T]hey have worked on the problem and tried to improve their products."

USP's Srinivasan concurs. "After the USP standards became official" in 1994, he says, "many companies started reformulating." One of them is SmithKline Beecham, makers of Geritol Complete, which failed the USP dissolution test previously. According to company spokesperson Leslie Ashburn, "We have identified the source of the dissolution issue and are reformulating Geritol to conform to USP standards. The reformulated product is expected to be available early next year." TwinLab, whose Calcium Citrate Caps also failed to dissolve, says it has reformulated already.

Still, Srinivasan cautions that "I would not be surprised" if there were current products out there that do not dissolve. Fortunately, there are a few steps consumers can take to increase the chances that the supplements they swallow will actually make it out of their digestive systems and into their bloodstreams for transport throughout the body.

* Buy supplements that have the letters "USP" on the label. "Manufacturers who go to the trouble of doing that generally tend to be more high-quality," Hoag comments.

They're also beholden to the law. The "USP" designation makes a company legally responsible to the Food and Drug Administration for meeting USP dissolution standards. Other USP standards must also be met if a bottle of pills has "USP" stamped on the label. One is a standard for disintegration, or the speed at which a tablet breaks down into small pieces (or mush) so that its nutrients can then go on to dissolve. Another is a standard for potency. In other words, the amount of vitamin or mineral in the tablet has to be the same as the amount claimed on the label. Finally, the pills must meet the USP standard for purity: They cannot be tainted by bacteria, harmful metals or other unwanted substances.

(The director of quality control for TwinLab, Bill McMahon, says Calcium Citrate Caps now meet the USP specifications but that it's "company policy" not to put "USP" on the label.)

* Don't be swayed by phrases like "timed release" or "sustained release." That's "a marketing gimmick," says Srinivasan, and consumers who buy into it "are wasting their money."

* Pass up "chelated" minerals, often available at health food stores. "Chelated" doesn't mean a mineral is absorbed better than one that's not chelated.

* Don't use price as a measure of a supplement's value. Some of the cheapest supplements on the market have the USP lettering on the label, a sign that their nutrients undergo dissolution. Some relatively expensive pills, on the other hand, do not sport any such assurances.

* If you take a multivitamin/mineral tablet, have it with a meal. Food slows the movement of nutrients through the gastrointestinal tract, which means your stomach and intestines have more time to break down the supplement. That, in turn, increases the chance that it will dissolve.

* Don't take supplements (or buy pills) that have passed their expiration date. Some nutrients degrade over time.

Lawrence Lindner is the executive editor of the Tufts University Health & Nutrition Letter.