All weeks
First Trimester
Week 4 of pregnancy
Your baby is the size of a poppy seed.
Length: 0.2 cm / 0.1 in
Baby at 4 weeks
- The blastocyst becomes an embryo — three layers form (ectoderm, mesoderm, endoderm).
- Each layer will form different organs (skin + nerves, muscle + bone, gut + lungs).
- Pregnancy hormone hCG starts to rise rapidly.
What you may feel
- Missed period — first sign for most women.
- Mild breast tenderness.
- Fatigue.
- Positive pregnancy test possible (sensitive home tests).
This week’s checklist
- Take a home pregnancy test if your period is late.
- Book your first GP / midwife appointment.
- Continue folic acid + start vitamin D 10 mcg/day (NHS).
Key milestone
Pregnancy test goes positive — hCG detectable.
Doctor / midwife visits
Call GP / midwife to book your first antenatal appointment.
Top foods this week
Educational only — not medical advice. Always consult your midwife or GP. Sources: NICE NG201 antenatal care, NICE NG207 inducing labour, NHS, RCOG. Read the full medical disclaimer.