The fetus can track light and dark through closed eyelids
Baby this week: about 40 cm — head to heel · about 1.3 kg
≈ 40 cm — about the size of a large butternut squash
Illustration enlarged for clarity — the amber marker shows true relative size
Your baby this week
- The fetus can now distinguish light from dark, even with eyes closed
- Amniotic fluid levels are near their peak, giving plenty of room to move
- Bone marrow has fully taken over red blood cell production
- Brain tissue continues to develop grooves and folds rapidly
Your body this week
- Fatigue can return as sleep becomes harder to find due to size and frequent bathroom trips
- Some people start noticing more frequent Braxton Hicks contractions
This week's tip: If you haven't already, this is a common time to start thinking about a birth plan and discussing preferences with your provider.
When to get help now
Contact your maternity unit now, even at night, if your baby is moving less than usual or the pattern has changed, you have any vaginal bleeding, fluid leaks from your vagina, you have regular or painful contractions before 37 weeks, or you have a severe headache, vision changes, pain just below the ribs or sudden swelling of the face, hands or feet. Do not wait until the next day.
Sizes and milestones are typical ranges — every pregnancy runs on its own clock. Educational content; your prenatal care team's guidance always comes first.