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13 weeks pregnant

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Your baby's development at 13 weeks

By the time you're 13 weeks pregnant, your baby is growing rapidly and is quite active, although their movement is still undetectable to you. Their reproductive organs are developed now and their liver and pancreas are beginning to function. Maintaining your healthy, balanced diet is essential, and this includes fibre to support healthy bowel function.

Alive and kicking in week 13

Your 13th week of pregnancy marks the start of your second trimester. By now, your baby weighs roughly 25g (almost an ounce)1. They are already very active and will be stretching, kicking and turning – however, you won’t feel any of this movement just yet.

 "Your baby’s development at 13 weeks"

Inside your baby’s body, their ovaries or testes have fully formed, and outside genitals will also be growing, although it’s still a little early to determine their sex1. Also at this stage, your baby’s liver will begin to produce bile and their pancreas will produce insulin1. Other developments include your baby’s vocal cords2, as well as their eyes and ears, which will be moving to the normal place on their head3.

Another important change is that your baby’s head will start to grow at a slower rate than the rest of their body. By week 21 it will be around 1/3 the size of their body, but at birth it will be 1/4 of the size3.

Focus on fibre

A balanced, nutrient-rich diet is important for you and your baby throughout pregnancy. Fibre is an essential element of this that will help support your digestion. However, most people in the UK don’t get enough (the average amount is 18g per day but the optimum is 30g4).

When you’re pregnant, getting adequate fibre is more important than ever, as hormonal changes in your body may cause you to become constipated5. Fibre can help maintain healthy bowel function.

There are two types of fibre. Insoluble fibre passes though the gut without being broken down and helps to move other food along with it. The other type of fibre is soluble fibre. Some soluble fibres can be fermented in the gut and provide a source of food for healthy gut bacteria.

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Increasing your fibre intake

Fibre is only found in foods derived from plants. Soluble and insoluble fibres are often found together in foods so eating a variety of good fibre sources should provide a beneficial mix of both types of fibre.

Good food sources of soluble fibre include6:

  • Barley, oats and rye
  • Beans and pulses
  • Fruit
  • Vegetables
  • Seeds

Some of the foods that provide insoluble fibre are6:

  • Wheat bran
  • Wholegrain cereals and breads
  • Brown rice
  • Fruit and vegetables
  • Seeds and nuts

Next Steps

Try the following food swaps to increase your intake of fibre:

  • Swap mashed potato for fibre-rich jacket potato
  • Instead of orange juice, have a whole orange
  • Swap vegetable soup for vegetable and bean soup
  • Instead of chicken curry and rice, have chicken and lentil curry with brown rice

View references

Hide references

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1. NHS UK. You and your baby at 13-16 weeks pregnant [Online]. 2013. Available at: [Accessed April 2014]

2. Murkoff H, Mazel S. What to Expect When You’re Expecting. 4th ed. London: Simon & Schuster Ltd, 2009.

3. Curtis GB, Schuler J. Your pregnancy week by week. 7th ed. Cambridge: Fisher books, 2011.

4. British Nutrition Foundation. Dietary Fibre [Online]. 2016. Available at: [Accessed July 2016]

5. NHS UK. Common health problems in pregnancy [Online]. 2013. Available at: [Accessed July 2014]

6. Cataldo C et al. Nutrition and Diet Therapy 6th Edition. Belmont USA: Thomson Wadsworth, 2003.

Last reviewed: 14th July 2016
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