It’s a no-brainer that you want to eat well when you’ve got a bun in the oven, but you may not realize how important certain nutrients are: A mild iodine deficiency during pregnancy could have a long-term effect on your child’s brain development, according to a new study published in The Endocrine Society’s Journal of Clinical Endocrinology & Metabolism.

Researchers at the Menzies Research Institute at the University of Tasmania in Australia looked at the iodine content in the systems of women who attended prenatal clinics. Then, nine years later, the researchers compared this information against the participants’ children’s standardized test scores. Seventy-one percent of mothers were found to have insufficient iodine levels—less than 150 micrograms per liter. On standardized tests, their children scored 10 percent lower in spelling, 7.6 percent lower in grammar, and 5.7 percent lower in English literacy.

Iodine, which the thyroid uses to make thyroid hormone, is important for a baby’s neurodevelopment, says Elizabeth Pearce, MD, associate professor at Boston University School of Medicine, who is unrelated to the study. A severe deficiency in iodine (anything less than 20 micrograms per day) can lead to a number of different neurologic abnormalities, including—in severe cases—intellectual disability, she says. On the other hand, overdosing on iodine might result in hypothyroidism—for both you and your baby. That’s why it’s mission critical for pregnant women to get the recommended amount: 220 micrograms per day if you’re pregnant, and 290 micrograms per day if you’re breastfeeding.

Hitting this sweet spot while you’re pregnant can be tricky. Since iodine isn’t labeled on food packaging, it can be difficult to know exactly how much you’re getting in your diet.

The easiest, most foolproof way to boost your iodine intake? Taking a prenatal multivitamin. Look for one that contains 150 micrograms of iodine, suggests Pearce. You may also want to consider checking the salt you use while cooking to make sure you’re grabbing the iodized version (although you don’t need to actively up your salt intake, says Pearce). Another food source that contains the nutrient: cow’s milk. Some of the iodine that the cows consume in their feeds transfers to the milk, and the dairy industry also uses iodine-containing cleansers to wash off milk equipment, which increases milk’s iodine content.

More from WH:
The 411 on Pregnancy and Depression
5 Ways Pregnancy Changes Your Body
What to Expect When You’re Expecting (After 35)

javahut healthy feed