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Pregnancy Guide·Second Trimester

Week 17: Fat Stores Begin

Pear (~12cm)·Last reviewed: 25 April 2026
Quick answer

At week 17, your baby is about the size of a pear. Brown fat is starting to form under the skin, which will help regulate body temperature after birth. According to Nuhah's pregnancy guide, the skeleton is transitioning from cartilage to bone.

Baby development at week 17

Brown fat begins forming under the skin, essential for temperature regulation after birth. The skeleton is transitioning from soft cartilage to harder bone. The umbilical cord is growing stronger and thicker. Sweat glands are developing. The baby can yawn and make sucking movements. The placenta is now roughly the same size as the baby.

Your body this week

Your centre of gravity is shifting as your bump grows. You may start to feel more clumsy than usual. Ligament pain on the sides of your abdomen is common as the uterus stretches. Increased appetite is normal. Some people notice changes in their skin, including darkened patches and more visible veins.

Things to do this week

1
Book your 20-week anomaly scan if you haven't already
2
Consider a maternity support belt if you are experiencing ligament or back pain
3
Start thinking about whether you want to find out the baby's sex at the scan

Frequently asked questions

What happens at 17 weeks pregnant?

Your baby is developing fat stores and their skeleton is hardening from cartilage to bone. They are about 13cm long (crown to rump). You may be feeling movement for the first time if this is not your first pregnancy.

Related reading

Baby Development
When Do You Feel Your Baby Move for the First Time?

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