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Your Third Trimester Guide

Your Third Trimester Guide

As you approach the end of your pregnancy and get ever closer to this new chapter in your life, you can feel all manner of wavering emotions and be overcome by an overwhelming excitement and eagerness around meeting your little one. Physically you may find things more challenging due to reduced energy levels or physical barriers (cue lace-free shoes). You may still have work and family obligations, but you will likely feel drawn to getting things ready for your new arrival. Remember to slow down in this trimester, as your body's natural instinct at this stage is to preserve and build energy stores for labour, healing and milk production.

Weeks 28-40

Disclaimer: Everyone's experiences  of pregnancy and their symptoms are different 

What physiological changes are happening:

Your baby can triple in size during this last trimester, growing from approximately a butternut squash to a watermelon, so it's not surprising women are often very ready for the end of the pregnancy by this stage. 

What your hormones are doing: 

Progesterone levels increase up to 10 times higher than other trimesters in the final trimester and this promotes placental growth and breast tissue maturation to allow milk production. It also promotes relaxed feelings that are often experienced during pregnancy. 

Thyroid hormone production also increases by 50% by the third trimester. This is to help the development of the foetal brain and to provide sufficient thyroid support for the mother. 

In the last month the body will also be working hard creating beta-endorphin, oxytocin and prolactin (for labour and milk production) and endorphins (our body's natural pain management team), but how well your body utilises them is dependent on sulphur-containing amino acids. Sulphur-containing amino acids can be found in: egg yolk, meat, organ meat and broths.  

The above hormones (beta-endorphin, oxytocin and prolactin) rely on good supplies of: 

  • Vitamin C: citrus fruit, kiwi fruit, green leafy veg, squash.
  • Copper, zinc and calcium: green leafy veg, bone broths, dairy products, lamb and beef.
  • B Vitamins: dark leafy greens, chickpeas, kidney beans, brussel sprouts, broccoli.   
  • Iron, magnesium: red meat, leafy green veg, lentils and nuts.

There is evidence that stress can affect birth progression due to its impact on beneficial gut bacteria and depletion of key birth and recovery nutrients (namely magnesium, vitamin c and b vitamins). Stress can also result in adrenaline being produced that can prevent birth progressing efficiently. Tip: try rest as much as possible and ask for help where you can, especially if you have existing children that require lots of care and attention. 

Food & drink during labour:

Labour can stimulate an emptying of the digestive tract, via sickness or diarrhoea. This is a common occurrence in the birth process but can cause dehydration so it's important to keep hydrated by sipping water or coconut water regularly. 

Include light snacks to support blood sugar levels, necessary for energising you during labour. Bare in mind that planned caesarean births are nil by mouth and if the hospital suspects you may have an emergency caesarean they may also request this (every hospital is different), so you want to make sure you get a sufficient energy intake in the final weeks before labour.

Raspberry leaf tea (rich in Vitamin C) can be included from 36 weeks and it helps to stimulate uterine muscles and ripens the cervix, in preparation for birth. 

Good snacks for labour:
A trail mix (nuts, seeds and dried fruit), banana, protein bars, a superfood blend that you can just add water to, bone broth and lastly some herbal teas,  such as nettle (for iron) and coconut water.

Batch cooking in preparation for postpartum:
Batch cooking and freezing meals pre-birth gives you a huge advantage when you are suddenly time-poor and preoccupied; soups, stews, bakes and protein bars or balls are all great options that are fast to heat once defrosted.

If you eat meat, try to include red meat in your diet to restore iron. This is especially important if you are breastfeeding as this is an energy-hungry process. Try to focus on protein, iron and zinc-rich foods which are all supportive for getting you back to balance postpartum. 

Common Symptoms: 

Heartburn: Seen most frequently in the last trimester of pregnancy, this is due to hormonal changes relaxing the muscle that prevents food from the stomach going back into the oesophagus. The growth of the baby can also increase pressure leading to symptoms. Try eating smaller, more regular meals so you don’t over-fill yourself when there is less room for food. Sleeping and sitting in a slightly raised position can also be beneficial. Try to avoid fatty and spicy food if you notice they increase occurrence.

Constipation: In the final months of pregnancy increased progesterone relaxes the muscles in preparation for labour. This can be intensified in the last trimester due to the weight of your baby and in some people this leads to constipation. Ensure you are eating fibre rich foods and keeping well-hydrated, as they will impact your gut motility. You may also find breathing techniques and elevating your feet on a stool help. Tip: Try soaking a tbsp of flaxseed in half a tumbler of water, leave for half an hour then drink or add to a smoothie.  

Insomnia: Often the stage of pregnancy that has the most disrupted sleep patterns, women commonly sleep less hours too (perhaps nature's gentle way of preparing the body for what comes next). Waking in the night can also be a result of discomfort, bathroom visits or nervousness about birth and motherhood. Tip: Don't eat anything for 2 ½ hours before sleeping and eat a smaller dinner. Your baby and food are now competing for precious space and this can result in feelings of fullness, heartburn and lighter sleep. 

Nutrients that are most important during this stage: 

As you approach the final weeks of pregnancy you may feel that you want to indulge. While this is completely normal and okay, remember to make the priority energising yourself for what is the marathon of labour. The physical and mental demands will be high and you will need to sufficiently replenish and preserve your energy stores in preparation for birth. You will need around 400 kcal extra in the last trimester due to another surge in growth. You will likely be feeling effects of the reduced space by now and your digestion also starts to slow towards the end of pregnancy. To keep up with the increased demand, try to eat little and often ensuring you are getting good sources of protein, fat and complex carbohydrates.  

Magnesium: A key nutrient for muscle contractions during labour and postpartum, it is also linked to healthy blood pressure levels. It is important to ensure good sources of dietary magnesium especially leading up to your due date. Magnesium has also been used as a calming mineral that can help with the wind-down towards bedtime when sleep may be harder due to the psychological demands on the body.
Sources: Green leafy vegetables, seeds, nuts, dark chocolate 85%+.

Iron: Undoubtedly important across all trimesters, but especially during the last three months as your baby will accumulate 2mg of iron a day. From 0-6 months, your baby will rely on these stores for oxygen transportation and lean muscle development and from 6 months they will rely on milk and food for iron. Premature babies are at a greater risk of deficiency. Tip: during your birth plan include a note for the midwife to only clamp the umbilical cord once it has stopped pulsing and white, as this can improve your baby's iron stores. Sources: nettle tea, green leafy vegetables, oats, pulses, spinach, organic red meat and lentils (always pair plant iron with vitamin C rich foods to aid absorption).

Vitamin K: This is the time to ensure you have good levels before birth as Vitamin K is a key player in effective blood clotting which is important during both vaginal and caesarean delivery..
Sources: Avocado, broccoli, beans, cabbage, lettuce, cauliflower, spinach, watercress, nettle tea, fermented foods. 

Omega 3: Essential fatty acids are important to include in your diet, especially during pregnancy. DHA (a type of omega 3) is important for normal brain and eye development of your baby in the third trimester. The mother-baby relationship is complex and intuitive and if you are not getting adequate omega 3 through your diet, the baby will pull on your own stores via the placenta, depleting maternal stores in the brain (the richest source). This may be where the term ‘baby brain’ originates, as low levels can result in forgetfulness and less sharp-thinking, especially in the last trimester and postpartum due to increased demand. Amazingly there is an estimated 2-3% shrinkage of the mothers brain during pregnancy. Source: Sardines, mackerel, anchovies, salmon, herring, trout, hemp, chia and flax seeds, walnuts (note that plant sources are far less well converted to rich DHA & EPA sources). 

Protein: Requirements go up to 50g per day during this last trimester to support the growth of your baby and to build energy stores in preparation for labour. It’s also key for keeping blood sugar stable. 
Sources: 100g chicken and 21-28g fish, 2 eggs, 300ml (½ pint) milk, 200g baked beans, 100g chickpeas/ kidney beans, 1 tablespoon nut butter, 1 small yoghurt 7g, 25g protein powder.  

Top Tip

Savour colostrum:
In the few days postpartum before your milk comes in you will be creating colostrum, a protein rich liquid that's full of immune supportive, antimicrobial properties. Some women get colostrum coming in before birth from around 37 weeks. If you have enough, try to collect this and store it in the freezer as you’ll then have some to give baby when they arrive (via an oral syringe). It can be a saving grace too if your baby gets poorly.   

Most importantly, enjoy this trimester where you can. Try and slow down and relish in the incredible work your body has done over the previous months. Think back through your pregnancy and all of the miraculous things you have accomplished and changes you have observed.

Prepare for your next trimester and read 'The Fourth Trimester Guide'.


Key takeaways:

  • Eat little and often as there is now less space due to baby’s increasing size. 
  • Ensure you are getting adequate protein & fibre in your diet. 
  • Batch cooking ahead of birth is a great way to ensure you will have nourishing meals at hand after birth. 
  • Try to rest as much as possible as you approach the final weeks of pregnancy to reserve energy stores.


Further reading:

Your Pregnancy Nutrition Guide - Henrietta Norton

Reference NHS guidance on what to avoid 





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