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13 weeks pregnant

Your baby at 13 weeks

Foetus at 13 weeks pregnant

Your baby is looking more like a little human. Her face is sorting itself out and the rate her body is growing has hurried up to catch up with her head. She is about 7.5cm long and weighs about 25g.

  • Your baby's eyes, which have been a bit to the side, now take up their rightful place looking straight ahead. Although closed, they'll be moving slowly under her eyelids. She can look as though she is making facial expressions - they are random but still cute.
  • Meanwhile, her ears are beginning to stand out a little on the side of her head.
  • It seems rather early but your baby's hair pattern is sorted out at this time.
  • All the time your baby's arms and legs are developing proper hard bones: the first bone that is formed is actually the clavicle, we have two - one each side at the base of our neck. The second is the thigh bone (the femur). If you have an ultrasound around this time you can see your baby is growing itself a skeleton.
  • Your baby's moving around quite a bit, kicking, flailing her arms and grasping with her hands. She has bursts of activity, stretching her legs and arms. Her muscles are developing, as are the nerves that make them work, and it's thought this activity is practice for the outside world so that each group of baby muscles knows what it's meant to do when it grows up.
  • She can open and close her mouth and stick out her tongue.
  • Her skin is still thin and transparent enough to be able to see blood vessels in places. Your baby doesn't have any fat yet, so she looks vaguely pink and skinny.
  • All the organs in your baby's body are continuing to grow. Her pancreas is producing insulin. Her stomach and bowels are all growing bigger and, on the inside, the bowel is developing little finger-like projections called villi, which absorb important nutrients from the food we eat into the blood stream.
  • Your baby's lungs are also growing and your baby will be practising how to breathe. She doesn't need to breathe 'properly' in your womb because her blood largely bypasses the lungs and gets the oxygen it needs through the umbilical cord. But as soon as she's born, she'll need to breathe because she'll need oxygen from the air around her - the umbilical cord and the placenta are history - so wisely, she has a gentle try-out before birth. Because she's surrounded by amniotic fluid, this means she's effectively breathing underwater.
  • Meanwhile, your baby's heart has already stormed ahead in development. If you hear its heart beat (through a Doppler machine that your midwife or doctor uses) it can sound alarmingly fast - like a mad galloping pony. This is normal. Your baby's heartbeat is around twice as fast as your own.

Your body at 13 weeks pregnant

  • Sickness You are likely to still feel sick. But you may find it's getting easier. Maybe you can now tolerate smells that, earlier on, were stomach turning.
  • Your rib cage You may be surprised if you are measured for a new bra that your back is bigger. This is because your rib cage has expanded at the bottom to cope with the increase in your breathing.
  • Your belly button It may already be sticking out alarmingly. It will end up as an outie - at least for the rest of the 40 weeks.
  • Your digestion Say hi to constipation and heartburn. Your digestive system slows down because of progesterone and oestrogen. It takes longer for food to get out of your stomach, hence the feeling it's still sitting there hours later. This slowing allows the maximum amount of nutrients to be reabsorbed from your body to fuel your foetus, but it leaves you prone to heartburn and constipation. Half of all women get constipated and half get heartburn. Some of you will be doubly blessed.
  • Heartburn will give you a pain behind your sternum (breast bone) that is usually worse when you lie down. You can also get a nasty acidic taste in your mouth from water brash (when the stomach digestive fluids rise up your oesophagus into your mouth). Discuss this with your antenatal team as simple over-the-counter remedies can help, but there are safe, more effective medicines if you need them. Avoid spicy, fatty foods and all foods just before bedtime. Yoghurt and milk can soothe the discomfort. (Heartburn is not a sign that your baby has lots of hair. This is a sweet myth.)



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: 3 months ago