§first trimester · week 4 of 40
you're 4 weeks pregnant.
last revised · baby is about 0.1 cm (0.04") · 0.04 g (0.00 oz)
about the size of a poppy.
Your baby is the size of a poppy seed. The embryo is implanting and forming three cell layers that will become every system in the body.
this week's highlights
- Implantation completes
- Neural tube begins forming
- Heart starts as a tube
- Placenta and amniotic sac form
how your baby looks
A tiny disc of three layers. The outer layer (ectoderm) becomes skin and brain, the middle (mesoderm) becomes bones and muscles, and the inner (endoderm) becomes organs.
body in focus
- head
- Neural tube begins forming — it will become the brain and spinal cord.
- body
- Three germ layers form, each destined to build entire body systems.
- hands
- feet
what's happening in your body
You may notice your missed period this week. Early hormones can bring breast tenderness, mild cramping, fatigue, or light spotting from implantation. A home pregnancy test is now reliable.
gentle tips
- Take a pregnancy test if your period is late — your body is producing HCG now.
- Schedule your first prenatal appointment for around week 8.
- Cut alcohol completely if you haven't already.
- Add folate-rich foods (lentils, spinach, fortified grains) to a daily meal.
- Note the first day of your last period for your provider.
what to expect next
The heart starts beating next week — a major early milestone. Pregnancy symptoms may begin showing up soon.