Trimester-by-Trimester Nutrition: What Changes and When

Pregnancy nutrition advice can feel like one long list that applies equally throughout, but in practice what your body — and your baby — needs shifts noticeably as pregnancy progresses. Knowing what matters most at each stage can help you focus your attention where it counts, rather than trying to do everything at once.

First Trimester (Weeks 1–12): Foundations, Not Extra Calories

The biggest misconception about early pregnancy is that you need to eat more. You don’t — calorie needs in the first trimester are essentially unchanged from before pregnancy. What matters far more is foundational nutrient intake, particularly:

• Folic acid — a 400mcg daily supplement is recommended from before conception (if possible) through at least week 12, to support neural tube development.
• Avoiding key risk foods — this is the trimester where getting food safety right matters most, since the neural tube and major organs are forming. Liver (vitamin A), unpasteurised dairy, and undercooked meat are worth being particularly careful about now.
• Managing nausea without losing nutrition entirely — see our morning sickness guide for practical approaches when appetite is unpredictable.

Many women find their appetite and food preferences change dramatically in the first trimester, sometimes making “ideal” nutrition hard to achieve. Eating what you can keep down safely matters more right now than eating a perfectly balanced diet.

Second Trimester (Weeks 13–27): Building and Absorbing

Nausea typically eases for most women during the second trimester, and appetite often returns — sometimes with a vengeance. This is the trimester where:

• Calorie needs rise slightly — around an extra 340 calories a day is a reasonable guide from the second trimester onwards, though this varies by individual.
• Iron demands increase as blood volume expands. This is also when your midwife will typically check for anaemia. See our iron-rich foods guide for food sources and absorption tips.
• Calcium and vitamin D matter more as your baby’s skeleton develops rapidly.
• Gestational diabetes screening typically happens between weeks 24–28 for those with risk factors, making steady, balanced blood sugar management relevant for many women from this point — see our gestational diabetes guide.

Third Trimester (Weeks 28–40): Peak Demand, Practical Constraints

The third trimester brings the highest nutritional demands of pregnancy, at the same time as practical eating often becomes harder — reduced stomach capacity from the growing bump commonly causes heartburn and a feeling of fullness after small amounts of food.

• Calorie needs rise further — roughly an extra 450 calories a day by the third trimester is a reasonable guide.
• Iron and calcium demands peak, supporting rapid growth and skeletal development in the final weeks.
• Smaller, more frequent meals often work better than three large meals as space in the stomach becomes limited — this also helps manage heartburn (see our heartburn and diet guide).
• Fibre and hydration become increasingly important as constipation is common in late pregnancy — see our constipation and fibre guide.

The Constant Throughout: Food Safety

Unlike calorie and nutrient needs, food safety guidance doesn’t meaningfully change by trimester — foods to avoid or treat with caution (unpasteurised dairy, undercooked meat, high-mercury fish, liver, and others covered throughout this site) apply for the whole nine months, not just early pregnancy, since the risks they carry — Listeria, Salmonella, Toxoplasma, excess vitamin A — remain relevant at every stage.

A Simple Way to Think About It

If you only remember one thing from each trimester: first trimester is about foundations and caution, second trimester is about building and steady absorption, third trimester is about peak demand met in practical, manageable portions. Your midwife will tailor specific advice to your circumstances at each antenatal appointment, so use this as general orientation rather than a substitute for that guidance.