What to Eat in the Third Trimester (Heartburn, Iron and No Room Left)

The third trimester is the point where your nutrition needs go up just as eating gets harder. Your iron needs are highest, DHA is building quickly in your baby's brain, and there's now a baby pushing up into your stomach. So the answer usually isn't eating bigger meals. It's changing the way you eat.

Why you need more food, even when you can eat less

US guidance puts the extra calorie figure at around 450 a day in the third trimester. UK guidance says around 200, and only in this final stretch. That is a wide gap between two reputable positions, so treat the range rather than picking a number.

The bigger issue is usually not how much you eat but how you eat. As your uterus presses upward, your stomach has less space, so a meal that felt fine at 20 weeks may feel heavy or uncomfortable at 34. Smaller meals eaten more often are usually the most helpful change, and they often help with heartburn too.

Iron matters most now

Plasma volume rises by roughly 40 to 50 percent across pregnancy, and the third trimester is when iron demand is at its highest. Your baby is also storing iron now, ready for life after birth, so this is the point where low intake or low iron stores can start to matter more.

Three things make a real difference:

• Pair plant iron with vitamin C in the same meal. Lentils with tomatoes, spinach with peppers, beans with a squeeze of lemon.
• Keep tea and coffee about an hour away from iron-rich meals, because they can reduce iron absorption.
• Let the blood test decide about supplements. Your doctor will check your iron levels during pregnancy. Iron supplements have real side effects, constipation among them, so use them only if you're struggling to get enough iron through food.

That's why the best iron-rich meals aren't just high in iron. They're built to help you absorb it well.

DHA is building fast in late pregnancy

DHA builds up in the fetal brain fastest during the third trimester. Omega-3 intake in pregnancy also has moderate evidence behind it for lowering the risk of early preterm birth, and that comes from Cochrane review data rather than supplement marketing.

Oily fish is the main food source, including salmon, trout, sardines, mackerel and herring. One to two portions a week is the usual recommendation, and no more than two portions of oily fish a week still applies. The fish to avoid stay the same, including swordfish, shark, marlin, king mackerel and bigeye tuna.

If you don't eat fish, it's worth bringing that up with your doctor. Plant omega-3 can convert to DHA, but the conversion is limited, so a supplement may make sense. Our fish and mercury in pregnancy guide will give you more info on the topic.

How to ease heartburn in the third trimester

Common, miserable, and mostly mechanical rather than dietary. What actually helps:

• Eat smaller meals more often, such as five small meals instead of three larger ones.
• Keep your evening meal lower in fat, because fat slows stomach emptying, which tends to make things worse at night.
• Try not to eat a large meal late, since lying down on a full stomach is a common trigger. It also helps to stay upright for a while after eating instead of reclining.

Trigger foods vary a lot between women, so a long avoid list is often less useful than noticing your own pattern. If heartburn is severe, constant, or stopping you from sleeping or eating properly, tell your doctor. You don't have to just put up with it, and there are safe ways to help.

What helps with constipation

Constipation is also common, and often worse if you are taking an iron supplement. The standard approach is fiber, fluids and gentle movement, increased gradually rather than all at once. If you suddenly eat much more fiber without drinking enough, constipation can get worse rather than better, so steady changes usually work best.

Whole grains, pulses, fruit, vegetables, nuts and seeds can all help. Fiber-rich recipes can make that easier without leaving you feeling too full. If constipation is persistent or painful, raise it with your doctor rather than trying to sort it out on your own.

Food safety rules still matter

Nothing on the food safety list changes near the end. Raw or undercooked meat, poultry, fish and shellfish still stay out. Liver and liver products still stay out. The high-mercury fish still stay out. Unpasteurized dairy still stays out.

Mold-ripened and blue cheeses are only safe if cooked until steaming hot. Cured meats should be thoroughly cooked until steaming hot. Caffeine stays at no more than 200 mg a day, and alcohol stays out. Check out the full list of foods to avoid.

Vitamin D at 10 micrograms a day continues through pregnancy and breastfeeding.

Fill your freezer before the baby arrives

Make your life easier during the first weeks after birth, because that's when cooking is least likely to happen, and eating well still matters for healing and recovery. Anything you freeze now is one less thing to think about later, and it's one of the few bits of preparation women often say really helped.

Freeze food on the day you cook it, in single portions so you can thaw just what you need. Cool and refrigerate it within one to two hours first. Defrost in the fridge rather than on the counter, and reheat until steaming hot all the way through. Rice needs extra care because cooked rice can carry a higher food poisoning risk, so it's often better made fresh.

Our postpartum freezer meals guide has the full version, including what freezes well, what doesn't, and how much is worth making.

A simple way to eat late in pregnancy

You don't need a perfect meal plan. What helps most is a pattern that fits your appetite, your stomach space, and the foods that you can eat. Here's an example:

• Breakfast: something with iron and fiber that doesn't need cooking, like apricot and cashew bircher made the night before.
• Mid-morning: fruit and a handful of nuts.
• Lunch: a pulse-based soup or bowl, with something acidic for the vitamin C.
• Afternoon: yogurt, or dates with almond butter.
• Dinner: oily fish twice a week, lower fat, moderate size.
• Evening: something small if you are hungry, not a second dinner.

Our third trimester recipes are built specifically for this window, weighted toward iron and omega-3.

Where to go next

• Postpartum freezer meals, the most useful thing you can do with a good week now.
• Fish and mercury in pregnancy, for the DHA question in full.
• Postpartum recipes, for what comes after.

Sources & further reading

• NHS: Vitamins, supplements and nutrition in pregnancy
• ACOG: Nutrition during pregnancy
• FDA/EPA: Advice about eating fish
• NHS: Foods to avoid in pregnancy
• Food Standards Agency: How to chill, freeze and defrost food safely