First Trimester: Complete Guide
The first trimester runs from week 0 (the first day of your last period) to the end of week 12, and it's often the most intense twelve weeks of pregnancy — even though there's little to show for it on the outside. Hormone levels climb fast, your body is quietly building the placenta, and most of the classic early symptoms (nausea, fatigue, sore breasts) show up here before easing off. This guide walks through what typically happens, what to prioritise, and when to get in touch with your midwife or GP.
What happens week by week
- Weeks 0-4: Ovulation, conception, and implantation happen, though most people don't know they're pregnant until a missed period around week 4.
- Weeks 5-8: Pregnancy hormone (hCG) levels rise quickly, which is often when symptoms like nausea and breast tenderness start. The embryo's major organs begin forming.
- Weeks 8-10: This is when most people contact their GP or self-refer to a midwife to get booked in for antenatal care.
- Weeks 10-12: Your booking appointment usually happens in this window, along with blood tests, a health and lifestyle discussion, and options for the 11-14 week scan (dating scan).
- Weeks 11-14: The dating scan confirms how far along you are, checks the baby's heartbeat and development, and may include combined screening for chromosomal conditions if you choose it. It's also the scan where "nub theory" — an early, informal, non-diagnostic guess at genital appearance — sometimes gets discussed, though it's for fun rather than a reliable prediction at this stage.
Common symptoms and what helps
Symptoms vary hugely between pregnancies, and plenty of people have a fairly easy first trimester. That said, the most commonly reported symptoms include:
- Nausea and vomiting ("morning sickness," though it can strike any time of day)
- Extreme tiredness, often more intense than normal fatigue
- Sore, heavier, or tingling breasts
- Needing to wee more often
- Mild cramping as the uterus stretches
- Mood swings and heightened emotions
Small, frequent meals, ginger, staying hydrated, and resting when you can all help with everyday nausea and fatigue. If sickness becomes severe — unable to keep fluids down, losing weight, or feeling dizzy and unable to cope — contact your midwife or GP, as this could be hyperemesis gravidarum, which needs proper medical support.
Getting your care and lifestyle right
- Book in early. Contact a GP or self-refer to community midwifery services as soon as you get a positive test — you don't need to wait until 12 weeks.
- Folic acid. Take a 400 microgram folic acid supplement daily from before conception (if possible) through to week 12, to support your baby's early neural development.
- Vitamin D. A 10 microgram vitamin D supplement daily is recommended throughout pregnancy.
- Food safety. Avoid unpasteurised soft cheeses, pâté, raw or undercooked eggs and meat, and limit oily fish, to reduce the risk of foodborne illness.
- Alcohol and smoking. The safest approach is to avoid alcohol completely and to stop smoking — ask your midwife or GP about stop-smoking support if you need it.
- Caffeine. Keep total caffeine intake to around 200mg a day or less (roughly one to two mugs of instant coffee).
- Gentle movement. Around 150 minutes of moderate activity a week is a reasonable target once you feel up to it, adjusted to how you're feeling.
When to seek help urgently
Contact your midwife, GP, or an out-of-hours service straight away if you experience heavy bleeding, severe one-sided abdominal pain, fainting, a high fever, or if sickness is so severe you can't keep any food or fluids down. These symptoms need prompt assessment and shouldn't wait for a routine appointment.
Frequently Asked Questions
When does the first trimester end?
The first trimester ends at the end of week 12, counted from the first day of your last menstrual period. From week 13 you move into the second trimester, when many people find symptoms like nausea and fatigue start to ease.
What's the most important thing to do in the first trimester?
Getting booked in with a midwife or GP as early as possible is the priority, alongside taking folic acid and vitamin D supplements. Early booking means you get blood tests, health checks, and your dating scan arranged in good time.
Is it normal to have no symptoms at all?
Yes. Symptom intensity varies enormously between people and even between pregnancies for the same person, and having mild or no symptoms doesn't mean anything is wrong. If you're ever worried, your midwife can reassure you or arrange a check, including an early scan if appropriate.
This article is for informational purposes only and does not constitute medical advice. Always consult your midwife or GP for guidance specific to your pregnancy.
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