Finding out you are pregnant can make the first few weeks feel exciting, uncertain and surprisingly busy. The first trimester is when many early pregnancy signs appear, your baby develops rapidly, and NHS maternity care begins. This first trimester pregnancy guide focuses on weeks 1-12 pregnancy, explaining what may be happening in your body, how your baby is developing and which practical steps are worth taking now.
What happens in the first trimester?
Pregnancy is dated from the first day of your last menstrual period, so the first two weeks are counted before conception usually happens. By the time a home pregnancy test turns positive, you may already be around four or five weeks pregnant. First trimester symptoms vary widely: some people feel nauseous and exhausted early on, while others notice very little.
Common symptoms include a missed or lighter period, tender breasts, tiredness, frequent urination, changes in taste or smell, bloating and nausea. Morning sickness can happen at any time of day and often begins around weeks 4 to 6. Symptoms alone cannot tell you whether a pregnancy is progressing normally, so avoid comparing your experience too closely with someone else’s.
First trimester week by week
Week 1
Week 1 starts on the first day of your last period. You are not yet pregnant biologically, but this date is used to calculate gestational age and your estimated due date.
Week 2
Your body is preparing to ovulate. In a typical cycle, an egg may be released around the end of this week or shortly afterwards, although cycle length varies.
Week 3
Fertilisation may occur around this stage. The fertilised egg begins dividing as it travels towards the uterus, where implantation can take place several days later.
Week 4
Many people first realise their period is late and take a pregnancy test. You may notice light spotting, breast tenderness, fatigue or no symptoms. Start or continue folic acid if you have not already done so.
Week 5
Hormonal changes may become more noticeable. Nausea, food aversions, frequent urination and tiredness can increase while early structures that will develop into your baby’s brain, spinal cord and organs are forming rapidly.
Week 6
Nausea and exhaustion may become stronger. Small, frequent meals and plain snacks help some people. If you cannot keep food or fluids down, contact your GP or maternity service because severe vomiting may need treatment.
Week 7
Your baby’s early limbs and facial structures continue developing. You may also feel more emotional or tired than usual, so give yourself permission to adjust routines and rest when needed.
Week 8
Make sure your maternity referral is underway. For example, if you discover you are pregnant at eight weeks, contact your local maternity service promptly rather than assuming you should wait for a routine GP visit.
Week 9
Your uterus is growing, although you may not look pregnant yet. Bloating can make clothes feel tighter. Keep eating a balanced diet, drinking enough fluids and choosing activity that feels comfortable.
Week 10
Your baby’s major body systems have begun forming and development continues quickly. NICE recommends that the first antenatal booking appointment should take place by 10 weeks where possible. The appointment covers your health history, medicines, lifestyle, emotional wellbeing and plans for antenatal care.
Week 11
Your baby continues to grow and become more recognisably formed. You may still experience nausea, headaches, constipation or tiredness. Some people begin to feel better soon, but symptoms do not follow a fixed timetable.
Week 12
You are approaching the end of the weeks covered here. In England, a dating ultrasound is usually offered around 10 to 14 weeks. It estimates how far along the pregnancy is and checks development. If you choose screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, part of that screening may also happen around this time.
Your first NHS antenatal appointments
Contact maternity services as soon as you know you are pregnant. At the antenatal booking appointment, a midwife usually asks about your medical history, previous pregnancies, medicines, family history, mental health and social circumstances. Routine checks can include blood pressure, urine testing and blood tests.
Your dating scan follows in the early pregnancy window. Screening is optional, and your maternity team should explain what is offered, what the tests can and cannot tell you, and when decisions need to be made.
First trimester health basics
Take 400 micrograms of folic acid every day until the end of week 12 unless a clinician has advised a higher prescribed dose. NHS guidance also recommends vitamin D in pregnancy; some people need a daily supplement throughout the year. Avoid supplements containing vitamin A as retinol unless specifically advised.
The safest approach is not to drink alcohol during pregnancy. Keep caffeine below 200mg a day and check pregnancy food-safety guidance for foods to avoid. If you already exercise, you can usually continue at a comfortable level. Do not stop prescribed medicines without speaking to the clinician responsible for your care.
When to seek medical help
Bleeding or pain in early pregnancy does not always mean something is wrong, but it deserves appropriate advice. Contact your GP, maternity service or NHS 111 if you are worried. Seek urgent help for severe or worsening one-sided abdominal pain, shoulder-tip pain, heavy bleeding, marked dizziness or fainting, as these can be warning signs of an ectopic pregnancy or another problem needing prompt assessment.
Frequently asked questions
When does the first trimester end?
Pregnancy terminology varies slightly between sources, but this guide covers weeks 1 through 12. Your midwife will date the pregnancy using your last menstrual period and information from the dating scan.
Is it normal to have no first trimester symptoms?
Yes. First trimester symptoms differ greatly between pregnancies, and having mild symptoms or none at all does not automatically indicate a problem. Contact a healthcare professional if you have specific concerns or worrying symptoms.
When should I arrange my antenatal booking appointment?
Start the referral process as soon as you know you are pregnant. NICE recommends a booking appointment by 10 weeks where possible, so early contact gives maternity services time to arrange your care and screening choices.
When is the first pregnancy scan?
In England, the dating scan is generally offered around 10 to 14 weeks. Your exact appointment depends on local services and your individual circumstances.
Moving beyond the first trimester
The first 12 weeks bring a lot of change, but you do not need to master pregnancy all at once. Focus on the essentials: arrange antenatal care early, take recommended supplements, review medicines with a professional, make sensible food and lifestyle choices, and seek help when symptoms worry you. Learning more about healthy eating in pregnancy, pregnancy-safe exercise and what happens in the second trimester can help you feel prepared for the months ahead.