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20 weeks pregnant

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Your baby's development at 20 weeks

Your baby’s cognitive and muscular functions are developing and so are their genitalia. Iron contributes to their cognitive development and it’s as important as ever that your balanced diet includes the right iron levels to support your baby’s continued progress.

Genital development in week 20

You are now halfway through your pregnancy, and by week 20 your baby will have grown to roughly 16cm from head to bottom and will weigh around 300g (10½ oz)1. Their heartbeat is now strong and can be detected easily. 

 "Your baby’s development at 20 weeks"

Baby girls will be developing a uterus, and their ovaries will contain primitive eggs, and the testes of baby boys will now be descending1. If you’re about to have your 20-week anomaly scan, your sonographer may be able to work out the sex of your baby, although your hospital may have a policy not to reveal this information2.

“…your sonographer may be able to work out the sex of your baby.”

Although the increase in your baby’s nerve cells is beginning to slow down, more complex connections are starting to form. In fact, your baby’s nervous and muscular systems have now developed enough to allow your baby to enjoy a satisfying stretch3.

Iron awe

Iron is a key nutrient throughout pregnancy, making up an important part of your balanced diet. Your blood cells need iron to carry oxygen round your body4 and to your baby. Iron also contributes to your baby’s normal cognitive function5.

“Your blood cells need iron to carry oxygen round your body and to your baby, whose cognitive development is supported by it.”

You’ll be routinely tested for anaemia (a condition caused by iron deficiency) during your pregnancy6, which will include assessing your haemoglobin and red blood cell levels. Many women have lower haemoglobin levels during pregnancy, but you’ll only be prescribed iron supplements if yours are very low7.

The Reference Nutrient Intake (RNI) of iron for most women – pregnant or not – is 14.8mg a day8. Eating enough iron-rich foods can help you maintain adequate levels.

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Adding iron to your diet

During pregnancy it’s especially important to think about what you eat. This is particularly pertinent to iron, as some foods can affect how much iron you can absorb.

"The phenolic compounds in tea and coffee, along with phytates in wholegrains and legumes can inhibit iron uptake."

While vitamin C improves iron uptake, calcium inhibits it, as can the phenolic compounds in tea and coffee, along with phytates found in wholegrains and legumes9. For this reason, it’s a good idea to drink a glass of fruit juice or eat a piece of fruit with high vitamin C content with or after eating iron-rich foods9.

Next Steps

Make sure you get enough of the following iron-rich foods:

  • Lean meat (always make sure it's well cooked) and oily fish, such as sardines
  • Dark green vegetables, including broccoli, watercress, spinach and kale
  • Nuts, especially cashew nuts
  • Pulses, chickpeas, beans and lentils
  • Wholegrains, including wholemeal bread, and iron-fortified breakfast cereals
  • Dried fruits, such as apricots, prunes and raisins
  • Eggs

View references

Hide references

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

2. NHS UK. Ultrascans in pregnancy [Online]. 2013. Available at: [Accessed July 2014]

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

4. European Union. Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children’s development and health OJ L 136 2012;1-40.

5. European Union. Commission Regulation (EU) No 957/2010 of 22 October 2010 on the authorisation and refusal of authorisation of certain health claims made on foods and referring to the reduction of disease risk and to children’s development and health. OJ L 279 2010;13-7.

6. National Institute for Health and Care Excellence. Antenatal Care CG62. London: National Institute for Health and Care Excellence, 2008.

7. NHS UK. Vitamins and nutrition in pregnancy [Online]. 2013. Available at: [Accessed July 2014]

8. Department of Health. Report on Health and Social Subjects 41. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. TSO: London, 1991.

9. Centres for Disease Control and Prevention. Iron and iron deficiency [Online]. 2011. Available at: [Accessed June 2014]

Last reviewed: 14th July 2016

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