It’s not hard to see why gummy vitamins are growing in popularity – what’s an easier sales pitch than a shortcut to good health embedded in a piece of candy? But gummy vitamins generally contain lower levels of nutrients than the traditional pills. For most of us, that’s not a serious concern since multivitamins probably don’t do much anyway. There are some people, however, for whom the stakes are higher — namely those trying to grow another human inside of their bodies.

Pregnancy is one condition for which the benefit of vitamin supplements including folic acid, iron and calcium, is well established. In fact, two large studies have recently confirmed that pregnant women who take iron are less likely to have babies with low birth weight. That’s why it’s notable and worrisome that retailers are selling a gummy vitamin labeled “Prenatal” that provides significantly fewer nutrients than normal prenatal vitamins.

The gummies attract women who have trouble taking the conventional supplements. “I had the worst time gagging every time I had to take the pills. They are just so huge,” said Sandra Young*. “I found the gummy ones and think they are amazing.” Young, who is in her second trimester, did not know that her gummies lacked iron.

Dr. Barbara T. Felt, a pediatrician at the University of Michigan, says women should consult their physician before using gummy vitamins, noting that the traditional prenatal vitamins were “formulated with the best evidence we have about the needs of the mother and fetus during pregnancy and after delivery.” Pregnant women might also want to note the following facts about some available prenatal gummy products:

The Vitafusion prenatal gummies now available on the shelves of every major drug store, as well as the generic copies sold by CVS and Target, do not contain calcium, thiamin, riboflavin, or iron – ingredients you’ll find in other prenatal vitamins. (Vitafusion has a separate gummy product called “Fiber+Calcium,” which is marketed as a companion supplement providing “Prenatal Support.”)

Dietary supplements do not require approval by the U.S. Food and Drug Administration, and although the manufacturers are not supposed to make misleading claims, there are no official requirements regarding what constitutes a “prenatal” supplement.

When it comes to iron, the gummy companies have a good reason for excluding the mineral. A representative for Church & Dwight, the household products corporation that purchased the Vitafusion brand last year, said she would not answer questions about the product. But the label on the bottle explains that the gummies don’t contain iron “because this product may appeal to children.”

Iron poisoning can be fatal to babies. In separate incidents in the early 1990s, five toddlers died in the Los Angeles area after consuming around 30 prenatal iron pills. “Iron tablets should be made less appealing to children by eliminating use of sugar coating or attractive colors,” the Centers for Disease Control and Prevention (CDC) advised at the time. Cases of iron poisoning in children subsequently decreased, and gummy-makers certainly don’t want to reverse that progress.

Still, the CDC and the American College of Obstetricians and Gynecologists recommended iron supplementation for pregnant women because it is usually difficult to obtain enough of the mineral from diet alone. The body uses iron to produce hemoglobin, the protein in red blood cells that transports oxygen, and during pregnancy, plasma volume increases up to 50%, lowering the blood hemoglobin concentration. A pregnant woman therefore needs more iron than non-pregnant women to maintain hemoglobin levels and prepare for the massive blood loss that happens on baby’s birthday.

When there’s not enough iron coming in, the blood cells will tap into the pregnant woman’s iron inventories and then, if the deficiency persists, red blood cells will decrease, eventually resulting in anemia. The mother-to-be will begin feeling week and tired and may have shortness of breath and problems concentrating. Although the fetus generally has first dibs on nutrients, in severe cases of iron deficiency, its health can also suffer.

A recent meta-analysis of trials conducted all over the world found that women who took iron supplements had babies that, on average, weighed around 2.4 ounces more than babies born to women who did not take iron. The study, by researchers at the Harvard School of Public Health, also demonstrated a dose–response relationship because the more iron women took (up to 66 mg per day), the lower the risk of both maternal anemia and low birth weight, which was defined as smaller than 5 pounds, 8 ounces. It was the second systematic review in the past year showing that iron supplements help prevent anemia during pregnancy and reduce the risk of low birth weight.

The concern about iron deficiency isn’t academic. Around 18% of pregnant women in the United States are iron deficient and 5.4% are anemic, according to a 2011 CDC study of samples taken between 1999 and 2006. The prevalence of iron deficiency was nearly 30% for certain subcategories of pregnant women, including those who have had more than two kids, those in their third trimester, and black women. Mexican-American women were also more likely (24%) than white women (14%) to be iron deficient during pregnancy. Minority women are less likely to use prenatal iron supplements, but they may be the ones who need them the most.

Women taking gummy prenatals may choose to add an additional iron supplement to their regimen or opt for a different product altogether, such as liquid or chewable supplements containing iron, if swallowing pills remains a challenge.

Ultimately, nutritional needs during pregnancy differ for each individual. Some women may not need extra iron, and for them, excess iron might be harmful. “All women who are expecting should seek prenatal care and talk about what is recommended with their physician since there may be special individual circumstances,” said Dr. Felt. With a simple blood test, doctors can monitor iron status throughout the pregnancy and determine, for each woman, whether the gummies are good enough.