5 WEEKS PREGNANT
The neural tube — the start of the brain and spinal cord — begins to close
Baby this week: about 0.2 cm — crown to rump · under 1 g
≈ 0.2 cm — about the size of a sesame seed
Illustration enlarged for clarity — the amber marker shows true relative size
Your baby this week
- The neural tube, which will form the brain and spinal cord, starts to close
- A primitive heart tube is taking shape and will soon start beating
- Three distinct layers of cells are forming, each destined to build different organs and tissues
- The embryo is curved, with a visible head fold and tail fold
Your body this week
- Fatigue and breast tenderness are common as hormone levels rise quickly
- Some people notice a heightened sense of smell or an early wave of nausea
This week's tip: This is a good week to start, or confirm, a folic acid supplement — doctors usually recommend one in early pregnancy, and yours will confirm the dose that's right for you.
Want the bigger picture — organ development, nutrition, scans and warning signs for this stage? See month 2: The heartbeat becomes real.
Sizes and milestones are typical ranges — every pregnancy runs on its own clock. Educational content; your prenatal care team's guidance always comes first.