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Pregnancy trimesters: what to expect week by week

Pregnancy is divided into three trimesters, each with distinct physical changes, tests and milestones.

First trimester (weeks 1–12)

The most symptom-intensive period for many women: nausea (affects 70–80% of pregnancies, typically improving by week 12–14), extreme fatigue, breast tenderness, frequent urination and heightened smell sensitivity. The 12-week scan (nuchal translucency) screens for chromosomal conditions. Many women don't disclose pregnancy until after this scan. Start folic acid (400mcg/day) ideally before conception and continue until week 12. Use our free symptom tracker to log the first trimester.

Second trimester (weeks 13–26)

The 'golden trimester' for most women — nausea typically resolves, energy returns, and the bump becomes visible. The 20-week anomaly scan is the most detailed scan in the pregnancy. Most people feel movement ('quickening') between weeks 16–22. Anaemia is common — iron-rich foods and supplementation if recommended. The baby's movements become increasingly distinct and should be tracked from around week 24.

Third trimester (weeks 27–40)

The preparation phase. Hospital bag by 36 weeks (babies are full term from 37 weeks). Birth plan discussed with midwife at the 36-week appointment. Reduced fetal movements (fewer than 10 movements in a 2-hour period after 24 weeks) should always be reported to the midwife on the same day — never ignore them. Use our free third trimester checklist to track every preparation task.

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Frequently asked questions

When should fetal movements be felt?
First pregnancy: typically weeks 18–22. Subsequent pregnancies: sometimes as early as 16 weeks (recognising the sensation more quickly). The NHS recommends contacting your midwife immediately if you notice reduced fetal movements after 24 weeks — any time, any day, including weekends. Never wait until the next scheduled appointment if movement has reduced.
What is the recommended weight gain during pregnancy?
NICE guidelines don't recommend routine weighing during pregnancy, but NHS guidance suggests: 11.5–16kg for a healthy weight woman. Your midwife will advise based on your BMI at booking. Excessive weight gain increases risk of gestational diabetes and complications; insufficient weight gain can affect fetal growth.