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15 weeks pregnant

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Your baby's development at 15 weeks

By week 15 of your pregnancy, the mechanisms within your baby’s ears are in place, although they can’t yet make sense of the sounds they hear. Learn why staying hydrated is an important part of your pregnancy diet, how to do it, and what happens if you don’t.

Sensory development in week 15 of pregnancy

Around week 15 of your pregnancy, your baby’s ears are developed enough1 to hear sounds from within your body, such as your heartbeat, voice and digestive system2. They can also pick up muffled sounds from the outside world2. However, the auditory centres in their brain aren’t functioning, so they can’t make any sense of these sounds yet1. Their eyes are also in the early stages of development, and although they are still fused shut, they now have some sensitivity to light2.

"Your baby’s development at 15 weeks"

“Your baby’s ear mechanisms are now developed enough to hear your heartbeat.”

When you are 15 weeks pregnant your baby’s skin is still very thin, and if you were able to look inside your womb, you’d be able to see their ribs and blood vessels under the surface1. They’re becoming increasingly active now, using their time awake as a chance to practise moving their body and flexing their muscles. They may even have started sucking their tiny thumb3.

Keep it fluid

It’s more important than ever to stay hydrated when you’re pregnant. The European Food Safety Authority recommends that women drink around 2 litres of water a day with an extra 300ml per day recommended during pregnancy4. That’s equivalent to about 9–10 250ml drinks per day.

“It’s more important than ever to stay hydrated when you’re pregnant.”

In addition to water, this includes all drinks like milk, fruit juices, squash, and even soup. Tea and coffee also count but it’s important to limit your intake of caffeine as drinking too much has been associated with an increased risk of miscarriage5. And, just like any other time, you’ll need more drinks in hot weather or after physical activity.

Why is it important to stay hydrated when you are 15 weeks pregnant?

The human body is approximately 60% water and loses on average 2 litres of water a day. It’s essential that this fluid is replaced to:

  • Avoid dehydration
  • Enable your blood to carry nutrients around your body and get rid of waste
  • Reduce the likelihood of getting urinary tract infections, which can be more common in pregnancy6
  • Maintain healthy bowel function
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How do I know if I’m dehydrated?

These are some of the signs that you may be dehydrated7:

  • Feeling thirsty
  • Passing dark-coloured urine infrequently (less than 3 or 4 times a day)
  • Dizziness or light-headedness
  • Headache
  • Tiredness
  • Dry mouth, lips and eyes

If you’re experiencing any of these symptoms, then make sure you drink more fluid as soon as possible.

View references

Hide references

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1. Deans A. Your New Pregnancy Bible, The experts’ guide to pregnancy and early parenthood. 4th ed. London: Carroll & Brown Publishers Limited, 2013.

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

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

4. European Food Safety Authority. Scientific Opinion on Dietary Reference Values for water. EFSA Journal 2010;8(3)1459:48.

5. NHS UK. Foods to avoid in pregnancy [Online]. 2013. Available at: [Accessed July 2014]

6. NCT. Kidney infection during pregnancy [Online]. 2012. Available at: [Accessed July 2014]

7. NHS UK. Dehydration symptoms [Online]. 2013. Available at: [Accessed July 2014]

Last reviewed: 14th July 2016

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