Prenatal vitamins have become a deeply ingrained part of the culture around pregnancy in the United States. Pregnant? You’d better be taking a prenatal. Thinking of getting pregnant? Ditto. Many would-be parents even start to take prenatals well before they attempt to conceive.

Prenatals became popular a few decades back, when research showed that folic acid intake during pregnancy can prevent neural tube defects (problems with the brain, spine, or spinal cord) in babies. Since then, the prenatal industry has boomed with literally hundreds of options, from your regular old drugstore brand to hyper-expensive organic supplements. How do you know which one to choose? Which one is best, and what should you look for when shopping?

The two most important ingredients in a prenatal? Folic acid (or folate) and iron. While there are certainly medical professionals and researchers out there who don’t believe that a prenatal vitamin does much to help during pregnancy (this mom’s OB actually told her to throw her bottle out!), the benefits of these two ingredients in the pills are key, says Dara Godfrey, a registered dietitian at Reproductive Medicine Associates of New York, a fertility clinic in New York City. Folic acid helps prevent the aforementioned neural tube defects in fetuses. Iron is key for fetal growth and development, and it also helps prevent anemia in the mother.

The vast majority of prenatals include those two ingredients, among with other common additives like magnesium, B vitamins, vitamin A, zinc to name a few. There are some professionals who think that prenatals that contain folate, rather than folic acid, are better. (Folic acid is the synthetic form of folate). Supposedly, folate, usually in the L-methylfolate form, is easier to digest and more bioavailable for the body. Nutritionist Stacey Bell told Reviews in Obstetrics and Gynecology in 2011 that about 40-60 percent of the population has genetic mutations that make it difficult to convert folic acid into the form needed by the body. While there’s still more research needed on this topic, it’s something to consider as you shop for prenatals. Ask your doctor or midwife about folate versus folic acid if you’re concerned.

But what else should you be on the lookout for when you’re browsing the supplement aisle or searching on Amazon? Godfrey says other vital nutrients to watch out for as you select a prenatal include vitamin D, calcium, and omega-3s. Make sure you get a prenatal with at least 400 IU of vitamin D (there is some evidence that low levels of vitamin D in pregnancy are associated with problems during pregnancy, like preeclampsia and bacterial vaginosis, although dosage recommendations to combat these conditions are highly variable). Food-based prenatals (where the nutrients come from food sources rather than synthetic sources) may be easier to digest, which is often a blessing during that queasy first trimester.

Unfortunately, labeling, formulation, and regulation of prenatal vitamins can be a bit dodgy here in the U.S. (A recent study in the Journal of the Academy of Nutrition and Dietetics found huge discrepancies between the vitamins and minerals in prescription vs over-the-counter prenatal vitamins, for example.) Because of this, Godfrey also suggests going for a name brand over a generic brand. “A generic brand may not contain the same ingredients/amounts found in a name brand (prenatals do not require FDA approval, and thus, do not have equivalence ratings),” she says. In her own practice, she recommends MegaFood Baby and Me Prenatal Vitamin, Deva Vegan Prenatal Multivitamin, and Nature’s Made Prenatal Multi + DHA.

The labels on many prenatals suggest users take multiple pills per day, sometimes multiple times per day, which can make it difficult for expectant parents to remember to take them. Hence the popularity of alternative forms of vitamins, like liquid and gummies. While the gummy form might appeal to those who can’t remember or have trouble swallowing pills, Godfrey says, “I recommend gel and capsule pills over gummies since they often don’t contain added sugars that are found in gummies. On top of the added sugars, I don’t suggest a gummy prenatal since it doesn’t contain iron.”

One more tip? Once you’ve found the right prenatal for you (feel free to try a few different brands and formulations until you find something that works), it’s best to take the supplement at night. Godfrey advises, “I suggest taking pills after dinner to help with absorption of the fat-soluble vitamins.”

Carrie Murphy is a freelance writer and doula in Albuquerque, NM. Read more on her website, carrie-murphy.com.