Third trimester
Week 33 of Pregnancy
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About the size of a pineapple
17.2 in · 43.7 cm · 4.23 lb · 1.92 kg (head to heel)
Your baby this week
- The skull stays deliberately soft and flexible — the plates will glide during birth.
- The immune system is developing, with your antibodies passing through the placenta.
- The brain and skull are growing quickly to finish the third trimester.
What you may be feeling
- Clamminess
- Occasional blurred vision from fluid shifts
- Nighttime awakenings
Gentle tips for this week
- Sudden vision changes with headache or swelling deserve a same-day call to your provider.
- Nap when you can — night sleep is officially fragmented.
Common question for week 33
Why is the baby's skull soft at birth?
The skull plates stay unfused so the head can mold and pass through the birth canal. The soft spots (fontanelles) close over the first 18 months or so after birth.
Every pregnancy is different. Sizes are averages, symptoms vary widely, and none of this replaces the guidance of your own provider.