DueDate.Baby

4 Weeks Pregnant: Baby Size, Symptoms and UK Milestones

First Trimester
Guide reviewed: July 2026Reviewed against cited UK guidance

At 4 weeks pregnant, use this UK guide to understand baby size, common symptoms, likely NHS timing, and the practical dates to keep on your radar.

4 weeks pregnant at a glance

  • You are in the first trimester.
  • Your baby is roughly the size of a poppy seed.
  • Contact your GP or local maternity service to register your pregnancy and book your 'booking' appointment.
  • Every pregnancy is different, so don't worry if your experience varies slightly.

You are 4 weeks pregnant and in your first trimester. Your baby is about the size of a poppy seed. This week's key development: Hello, Little One. NHS note: Contact your GP or local maternity service to register your pregnancy and book your 'booking' appointment.

Taking a Pregnancy Test

Week 4 is typically when a home pregnancy test will show positive because your period is due. The test detects the hCG hormone which starts being produced after implantation.

This page is for general pregnancy planning and date guidance only. It is not medical advice, diagnosis, or treatment. Pregnancy dates are estimates and can change after a scan or advice from your midwife, GP, or maternity team.

If you have symptoms, concerns, or questions about your pregnancy, speak to your midwife, GP, or maternity team. For urgent help, use NHS 111; call 999 in an emergency. Read how we source and review content in our editorial policy.

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Baby's Development

Your baby is about the size of a poppy seed.

Hello, Little One — Implantation is complete and your body is producing hCG, the hormone a home pregnancy test can now detect. Tiny layers of cells are already differentiating into what will become your baby's brain, spine, and heart.

Illustration of a poppy seed, showing the approximate size of the baby at week 4
Poppy seed
Approx. 0.2cm

Your Symptoms

  • Missed period
  • Tender breasts
  • Fatigue
  • Mild nausea

Every pregnancy is different. You may experience all, some, or none of these symptoms — and that's completely normal. If anything concerns you, speak to your midwife.

NHS Appointments

Contact your GP or local maternity service to register your pregnancy and book your 'booking' appointment.

Practical Advice for Week 4

Nutrition

  • Continue folic acid and vitamin D daily.
  • Eat wholegrain carbohydrates for sustained energy — brown rice, oats, wholemeal bread.
  • Stay hydrated, especially if you're experiencing early nausea.
  • Avoid soft cheeses with white rinds (brie, camembert) and blue cheeses.

Exercise

  • You can safely continue most exercises, including running and gym classes.
  • Listen to your body — if something feels wrong, stop and rest.
  • Pelvic tilts can help strengthen your core for the months ahead.
  • Avoid hot yoga or exercising in extreme heat.

Wellbeing

  • Fatigue is very real right now — your body is building a placenta. Rest guilt-free.
  • It's okay to feel overwhelmed, excited, scared, or all three at once.
  • Talk to your partner about when and how you'd like to share the news.
  • If morning sickness hits, know that it usually peaks around weeks 8–10 and then eases.

Preparation

  • Contact your GP or self-refer to your local maternity service to register your pregnancy.
  • Your booking appointment should be scheduled between weeks 8 and 12.
  • Find out about the free NHS Maternity Exemption Certificate (MatEx) for prescriptions and dental care.
  • Download your hospital trust's app or online portal if they have one.

Tip of the Week

A positive home pregnancy test is very reliable. You don't usually need a GP to confirm it.

Frequently Asked Questions for Week 4

How many months is 4 weeks pregnant?
At 4 weeks pregnant, you are roughly in your first month pregnant. Remember that pregnancy is typically measured in weeks rather than months for clinical accuracy.
What size is the baby at 4 weeks?
At 4 weeks, your baby is roughly the size of a poppy seed (about 0.2cm). Implantation is complete and your body is producing hCG, the hormone a home pregnancy test can now detect. Tiny layers of cells are already differentiating into what will become your baby's brain, spine, and heart.
What are the common symptoms at 4 weeks pregnant?
Common symptoms at this stage include missed period, tender breasts, fatigue, mild nausea. Remember that every pregnancy is unique, and it's normal to experience different symptoms.
Is 4 weeks in the first trimester?
Yes, 4 weeks falls within the first trimester.
Are there any NHS appointments at 4 weeks?
Contact your GP or local maternity service to register your pregnancy and book your 'booking' appointment.

Tools & Calculators

Due Date Calculator UKPregnancy Week CalculatorTimeline by Due DateHow Many Weeks Am I?

Sources and further reading

Checked for UK week 4 pregnancy information guidance in July 2026.

How we review content

We prioritise official NHS and GOV.UK guidance, then relevant professional-body information where needed.

Source links are checked on the review date shown above. Your midwife, GP, maternity team, fertility clinic, or employer can give advice that is more specific to your circumstances.

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Track Your Due Date

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NHS Resources

Find trusted information on financial support, antenatal classes, and local maternity services.

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All Weeks

Browse the complete week-by-week pregnancy guide from conception to birth.

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