Week 4 Pregnancy

First Trimester

Last reviewed: July 2026

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. Always speak to a qualified healthcare professional if you have symptoms, concerns, or questions about your pregnancy.

Week 3

Week 5

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.

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.