During the third trimester, your baby is gaining weight rapidly, building bone, and undergoing a surge of brain development. You need roughly 300 extra calories per day compared to your pre-pregnancy intake, but what matters more than the calorie count is where those calories come from. The final 12 weeks place specific demands on certain nutrients, and the right foods can also ease common late-pregnancy discomforts like heartburn and constipation.
DHA for Rapid Brain Growth
Your baby’s brain accumulates DHA, an omega-3 fat, faster during the third trimester than at any other point in pregnancy. DHA also concentrates in the retina, and that buildup is essentially complete by birth. International guidelines recommend pregnant people consume at least 200 mg of DHA per day on top of a baseline of 250 mg of combined omega-3s. If your intake has been low (under 150 mg of DHA daily), a clinical guideline published in the American Journal of Obstetrics & Gynecology suggests increasing to 600 to 1,000 mg per day starting no later than 20 weeks.
The best food sources are fatty fish like salmon, sardines, herring, and trout. Two to three servings of low-mercury fish per week will cover most of the requirement. If fish isn’t part of your diet, a DHA supplement derived from algae or fish oil is a reliable alternative.
Calcium and Your Baby’s Skeleton
By 35 weeks, your body transfers roughly 330 mg of calcium to your baby every single day, up from about 50 mg at 20 weeks. That’s a dramatic increase, and if your diet doesn’t supply enough, your body will pull calcium from your own bones. The goal is to keep your intake well above 600 mg daily, the level below which most adults slip into a negative calcium balance.
Dairy products are the most concentrated sources: a cup of milk or yogurt delivers around 300 mg. Fortified plant milks, tofu made with calcium sulfate, canned sardines or salmon with bones, and leafy greens like kale and bok choy all contribute. If you’re consistently eating three servings of dairy or fortified alternatives per day, you’re likely in good shape.
Choline for Fetal Brain Development
Choline is one of the most under-consumed nutrients in pregnancy, yet it’s critical for your baby’s brain. Your body transports choline to the fetus at a high rate, and a deficiency can interfere with normal brain development. The adequate intake is set at 450 mg per day during the third trimester, though some researchers recommend closer to 600 mg for this stage of pregnancy, particularly for people who don’t eat eggs regularly.
Eggs are the single richest common food source, with about 300 mg of choline in two large eggs. Beef liver is even more concentrated but less popular. Beyond eggs, chicken, fish, soybeans, and cruciferous vegetables like broccoli and Brussels sprouts contribute smaller amounts. If your diet is low in these foods, look for a prenatal supplement that includes choline, since many standard formulas leave it out.
Iron and Increased Blood Volume
Your blood volume expands by 30 to 45 percent during pregnancy, peaking around 32 to 34 weeks. That expansion requires a significant increase in red blood cell production, which drives iron demand to 27 mg per day, roughly triple the recommendation for non-pregnant adults.
Red meat, poultry, and shellfish provide the form of iron your body absorbs most efficiently. Plant sources like lentils, chickpeas, fortified cereals, and spinach contribute too, though you’ll absorb more from these if you pair them with a source of vitamin C, such as bell peppers, tomatoes, or citrus. Most prenatal vitamins contain iron, but food sources help fill the gap and provide other nutrients at the same time.
Fiber to Manage Constipation
Constipation is one of the most common third-trimester complaints, driven by hormonal changes and the physical pressure of your growing uterus on your digestive tract. The American College of Obstetricians and Gynecologists recommends aiming for about 25 grams of fiber per day. If you haven’t been hitting that number, increase gradually rather than all at once to avoid bloating, and drink plenty of water alongside the extra fiber.
Some of the best sources include raspberries, lentils, split peas, apples, bananas, and whole-wheat pasta. Checking labels on packaged foods for higher-fiber options is an easy habit that adds up. A bowl of oatmeal topped with berries at breakfast and a lentil-based soup at lunch can get you more than halfway to the target.
Steady Energy From Complex Carbohydrates
In the third trimester, your body becomes naturally more resistant to insulin, which means blood sugar can spike more easily after meals heavy in refined carbs. Research published in the journal Nutrients suggests that choosing higher-quality carbohydrate sources with a low glycemic index and minimal added sugar helps control blood sugar levels throughout pregnancy.
In practical terms, this means choosing whole grains (brown rice, quinoa, oats, whole-grain bread) over white bread and sugary cereals. Sweet potatoes, beans, and lentils are excellent choices that also deliver fiber and other nutrients. You don’t need to avoid carbohydrates. They should make up a substantial part of your diet. The emphasis is on quality: foods that break down slowly and keep your energy level stable rather than causing a spike and crash.
Vitamin K Before Delivery
Vitamin K is essential for blood clotting, which matters as your body prepares for birth. Transport of this vitamin across the placenta is limited, so newborns are at higher risk of deficiency. Eating vitamin K-rich foods in the final weeks supports your own clotting ability heading into labor. The adequate intake during pregnancy is 75 mcg per day, and green leafy vegetables make it easy to exceed that.
Half a cup of cooked collard greens provides 530 mcg, and a cup of raw spinach has 145 mcg. Broccoli, kale, and turnip greens are also rich sources. Even using soybean or canola oil for cooking adds a modest amount. If you’re eating a salad or a serving of cooked greens most days, you’re well covered.
Staying Hydrated
Your fluid needs increase during pregnancy to support expanded blood volume, amniotic fluid, and the extra demands on your kidneys. The American Institute of Medicine recommends a total water intake of about 2,700 mL per day (roughly 11.5 cups) for pregnant people. That total includes water from food, so you don’t need to drink all of it from a glass, but aiming for 8 to 10 cups of fluids is a practical starting point.
Water is the best choice. Milk, herbal teas, and broth count toward your total. Adequate hydration also helps with constipation and can reduce the frequency of headaches and urinary tract issues that become more common in late pregnancy.
Eating Patterns That Ease Heartburn
Heartburn affects a large percentage of people in the third trimester as the uterus pushes up against the stomach and hormonal changes relax the valve between the esophagus and stomach. How you eat can matter as much as what you eat.
Smaller, more frequent meals put less pressure on your stomach than three large ones. Avoiding greasy and spicy foods, tomato-based sauces, highly acidic citrus products, carbonated drinks, and caffeine can reduce symptoms. A consensus guideline on heartburn in pregnancy also recommends not lying down within three hours of eating, which means finishing your last meal or snack well before bedtime. These adjustments won’t eliminate heartburn for everyone, but they’re the recommended first-line approach and often make a noticeable difference.
Putting It All Together
A typical day of eating in the third trimester doesn’t need to be complicated. Breakfast might be oatmeal with berries and an egg. A midmorning snack of yogurt covers calcium and gives you a protein boost. Lunch could be a lentil soup with whole-grain bread. An afternoon snack of apple slices with nut butter adds fiber and healthy fat. Dinner built around salmon, brown rice, and a side of sautéed greens hits DHA, iron, vitamin K, and complex carbs in a single plate.
The recurring theme across all these nutrients is that whole, minimally processed foods do the heavy lifting. Leafy greens, eggs, fish, legumes, whole grains, and dairy or fortified alternatives cover nearly every increased demand of the third trimester. A good prenatal vitamin fills in any gaps, particularly for iron, DHA, and choline, but food remains the foundation.