Mumsnet pregnancy calendar

1st trimester

2nd trimester

3rd trimester

17 weeks pregnant

Your baby at 17 weeks

Foetus at 17 weeks pregnant

She is now about 13cm from her crown to her rump and weighs about 140g.

You could hold your baby in the palm of your hand but she is getting plumper. The placenta is nearly as big as she is. 

  • She is putting down layers of fat and starting to fill out some of those wrinkles of skin. She forms some special kind of fat, called brown fat, that will insulate her when she's born. It's found at the back of her neck and around her kidneys.
  • Inside her brain the nerve cells are connecting to each other more and more. Her eyes are still shut but she can roll them side to side and her retina can now react to light.
  • She's hectic, doing somersaults and kicking more forcefully. She will move away from any pressure on your abdominal wall - an ultrasound probe can make her jump.
  • There are some downsides to being in an amniotic fluid bath for nine months and so your baby develops some protection in the form of a cheesy, white cream that covers her whole body and head. Called vernix, it's made from the baby's sebaceous glands (the ones that make oily fluid to protect our skin) and acts as a waterproof layer to protect your baby's delicate skin from getting chapped by the amniotic fluid. It makes it easier for your baby to get through the birth canal but makes her slippery when she comes out. You'll see the remnants of it on your baby's skin at birth.
  • At 17 weeks she is starting to make meconium - her first bowel movement - which consists of bile salts and acids made in her liver and skin cells she has swallowed from the amniotic fluid. 

Your body at 17 weeks pregnant

  • Energy levels The textbooks say you feel more energetic now, though some women just feel heavy and cumbersome. But generally women feel less sick and tired, and see these weeks as the ideal time for a final, child-free holiday.
    If you do go on holiday, take your hand-held notes and don't go scuba diving as decompression sickness is too much of a risk for your baby. You may want to choose a country with good standards of food hygiene, to avoid food poisoning. You'll get hot and tan faster than you pre-pregnancy self because the amount of blood going round your body has increased and more is going to your skin and mucous membranes. You will feel more sweaty than usual in the heat.
  • Circulation Your heart is pumping more blood faster round your body and, to avoid your blood pressure going up, your pregnant body adapts by making your blood vessels more elastic. They can then expand to take the extra blood. You may be more aware of your heart beat and you can feel occasional missed beats, which is normal. But if you feel that your heart is beating irregularly you should see your doctor.
  • Sex Your libido may come back just as your waistline is vanishing. This happens because being more obviously pregnant usually helps you get used to it. You will also be less sick and exhausted.
  • Baby brain Some pregnant women swear they get fuzzy-headed and forgetful. The research shows conflicting results. A study in the British Journal of Psychiatry from Australian researchers said that baby brain is not a real phenomenon. The researchers tested how quickly over 1,200 women could think and aspects of their memory. They then repeated the tests as the women became pregnant. There was no difference in the results. You may think your brain is working differently, but actually you may just be focusing on different areas of your life eg which pushchair to buy rather than which strategy paper to read at work. However, other studies do show memory lapses, especially at high levels of thinking and intellectual problem solving. Getting enough sleep will help you think more clearly.



Pregnancy Encyclopedia book coverIllustrations taken from The Pregnancy Encyclopedia, £25, published by DK.

Disclaimer: The information in the pregnancy calendar is for general information and is not intended as a substitute for the medical advice of your own doctor or antenatal team. Not all babies develop at the same time and in the same way, so this week-by-week guide may not always match your own experience. If you have any worries, consult your antenatal team or GP.

Last updated: 4 months ago