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21 weeks pregnant



Your baby's development at 21 weeks

By the time you’re 21 weeks pregnant, your baby weighs more than your placenta. Their digestive system is starting to work and their bones are becoming harder and stronger. Learn how certain fats are important for their development at this time, and how to get a healthy serving of them in your daily diet.

Swallowing and experiencing taste in week 21 of pregnancy

Weighing around 350g (just over 12oz)1, in week 21 of pregnancy your baby weighs more than the placenta. Their movements may be increasingly noticeable from now on as the cartilage in their body turns to bone, giving their limbs and joints more substance and strength2.

 "Your baby’s development at 21 weeks"

Your baby’s digestive system has started functioning at this stage, albeit in a simple way3. One action thought to help their digestive system develop is swallowing amniotic fluid, which is also a source of nourishment for your baby3. Naturally sweet, your amniotic fluid takes on subtle flavours of the food you eat each day2, which your baby experiences thanks to their increasingly sensitive taste buds4.

Many of your baby’s activities can be seen on an ultrasound now, including swallowing3 and sucking their thumb4. What you may never see is the fine hair called lanugo that covers their body until the later stages of pregnancy, when fat takes over the job of keeping them warm1.

Omega 3 and Omega 6 fats

Omega 3 and 6 are two groups of fatty acids, including long chain polyunsaturated fatty acids (known collectively as LCPs). One of the Omega 3 LCPs is called docosahexaenoic acid, or DHA for short. During pregnancy, DHA contributes to your baby’s brain development and also supports the development of your baby’s eyes5. It is also associated with development in infancy, contributing to the normal visual development of your baby throughout the first year5.

"Include DHA in your second trimester diet to support the development of your baby’s brain and eyes.”

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LCPs – a hot topic of research

Experts have recently reviewed the evidence around the impact of LCPs in pregnancy. It’s been shown that taking extra DHA during pregnancy reduces the risk of preterm delivery and increases the birthweight of babies6,7.

For this reason, pregnant women are advised to include sufficient levels of Omega 3 fats in their diet, particularly DHA.

A daily dose of healthy fats during pregnancy

During pregnancy you should try to include an extra 200mg of DHA every day for normal eye development of the foetus5. The best sources of DHA are oily fish like mackerel, sardines and salmon. However, experts advise limiting certain types of fish in pregnancy because of the levels of toxins they can contain. Supplements are available but it’s a good idea to talk to your midwife or GP to check if a supplement is necessary.

For a healthy, safe intake, aim to eat 1–2 portions of oily fish per week. If you don’t like eating oily fish, be sure to include some other sources of Omega 3 fats in your diet such as nuts, seeds, dark green vegetables, rapeseed oil, wholegrain cereals and soya products8. While your body can convert some of the Omega 3s in these foods into DHA, it is thought that this process is not very efficient, and they’re not a particularly good substitute for oily fish.

Next Steps

Try these Omega 3 rich snacks and small meals:

  • Mackerel on a slice of wholegrain toast
  • Grilled salmon with steamed vegetables
  • Salmon fishcakes
  • A handful of nuts and seeds
  • A bowl of wholegrain cereal

View references

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1. NHS UK. You and your baby at 21-24 weeks pregnant [Online]. 2013. Available at: [Accessed July 2014]

2. Murkoff H, Mazel S. What to Expect When You’re Expecting. 4th ed. London: Simon & Schuster Ltd, 2009. p. 231.

3. Curtis, GB, Schuler, J. Your pregnancy week by week. Cambridge: Fisher books, 2011. p. 297.

4. Deans A. Your New Pregnancy Bible, The experts’ guide to pregnancy and early parenthood. 4th ed. London: Carroll & Brown Publishers Limited, 2013. p. 40.

5. European Union. Commission Regulation (EU) No 440/2011 of 6 May 2011 on the authorisation and refusal of authorisation of certain health claims made on foods and referring to children’s development and health. OJ L 119 2011;4-9.

6. Carlson SE et al. DHA supplementation and pregnancy outcomes. Am J Clin Nutr 2013;97(4):808-15.

7. Imhoff-Kunsch B et al. Effect of n-3 long-chain polyunsaturated fatty acid intake during pregnancy on maternal, infant, and child health outcomes: a systematic review. Paediatric and perinatal epidemiology 2012;26(1):91-107.

8. Gandy J (ed). Manual of Dietetic Practice. 5th ed. Oxford: Wiley Blackwell. 2014. p. 759.

Last reviewed: 14th July 2016

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