17 weeks pregnant: baby is the size of a pear

Your baby this week

Your baby's skeleton is changing from soft cartilage to bone, a process that will continue after birth. Fat is starting to form under the skin, including a special type called brown fat that helps a newborn stay warm. The umbilical cord is thickening and getting stronger. Sweat glands are developing, and your baby's skin is still thin and covered in fine downy hair.

Your baby is highly active. Yawning, hiccupping, stretching, turning and rolling all happen inside the amniotic sac. The brain is developing areas linked to the senses and movement.

How it happens. Your baby has plenty of room to move, and movement itself helps the joints and muscles form. This is why activity in the womb is a sign of healthy development.

Your body this week

Your uterus is about at the level of your belly button in some people, and lower in others. Your bump may be more noticeable, and your centre of gravity is shifting. The hormone relaxin is softening your ligaments, and this can make you feel less stable.

Your appetite and energy are usually good, but as your body works harder you may feel warm or short of breath when you climb stairs.

What do first movements feel like?

Quickening is the name for feeling your baby move for the first time. Many describe it as a flutter, a tickle, popping bubbles, a light tap or a fish swimming. It is easy to mistake for gas or hunger.

When you feel it depends on several factors. People who have been pregnant before often notice movement from 16 weeks, since they know what to look for. First-time parents commonly feel it between 18 and 22 weeks, and some notice it later. The position of your placenta, your body shape and how active your baby is all play a part. If your placenta is at the front of your uterus, it can cushion movements, so you may feel them later.

Tips for noticing movements:

• Lie down on your side and relax. Movements are easier to notice when you are still.
• Try after a meal. A rise in blood sugar can make your baby more active.
• Do not worry about counts yet. There is no set number of movements at this stage, and your baby's pattern will become clearer over the coming weeks.

If you have not felt anything by 24 weeks, mention it to your provider.

What the placenta does

The placenta is a flat, round organ that attaches to the wall of your uterus. It grows throughout pregnancy and, by birth, weighs about 500 g (a little over a pound). It has several jobs:

• Delivering oxygen and nutrients. Blood from you passes close to your baby's blood without the two mixing, and oxygen and nutrients move across.
• Removing waste. Carbon dioxide and other waste products pass back to you.
• Making hormones. The placenta produces hCG, progesterone, estrogen and others that support pregnancy.
• Providing partial protection. Some antibodies pass across, giving your baby early immunity. It is not a perfect barrier, and some infections, alcohol and certain medicines can cross it.

Your anatomy scan at 18 to 22 weeks will check where the placenta sits. In some pregnancies it lies low, close to or over the cervix. This is called a low-lying placenta or placenta previa, and it is often found early. In many cases it moves upward as the uterus grows, and your provider will arrange another scan later to check. If you have painless bleeding in the second or third trimester, call your provider or go to hospital straight away.

Feeling clumsy

If you drop things or bump into furniture, you are not imagining it. Relaxin loosens ligaments to prepare for birth, your centre of gravity is moving forward, and you may have less sensation in your hands. Wear flat, supportive shoes, take care on stairs and wet floors, and slow down when you turn. If you fall, call your provider, even if you feel fine.