Everything you need to know about your third trimester

As you welcome in the third trimester (weeks 28-40), you inch closer to meeting your baby. This stage of pregnancy is often earmarked by a full spectrum of emotions – excitement, trepidation, and overwhelm. Physically speaking, things can become harder, and you may want to go into hibernation mode. This is normal; your body’s instinct is to slow down during your third trimester to preserve energy stores for birth and milk production.
 

Hormonal changes during the third trimester

 
Some notable hormonal changes happen in your third trimester. This stage of pregnancy sees your body gearing up for labour and bonding with your baby.
 

Oestrogen

 
Oestrogen is sky-high as you enter your third trimester, peaking around week 32. Elevating oestrogen helps prepare your body for breastfeeding if you choose to. It also works with oxytocin to prepare your uterus for labour (1).
 

Progesterone

 
Progesterone also peaks around week 32. Progestogen causes the sphincter at the base of the oesophagus to relax, which may lead to acid reflux and heartburn (2).
 

Prolactin

 
During the third trimester, prolactin prepares your breast tissues for lactation to feed and connect with your baby (3).
 

Oxytocin

 
Also known as the ‘love hormone’, oxytocin supports milk production and helps you bond with your baby. It also reduces pain during labour and, in combination with oestrogen, triggers the release of prostaglandins, which help soften the cervix in preparation for birth (4).
 

Foetal developments during the third trimester

 
During the third trimester, your baby continues to grow in the third trimester. They can see and hear now. They can suck their thumb and have the ability to cry. Their brain, kidneys, and lungs grow and mature. They gain more weight and start to prepare for delivery. By week 40, your little one is the size of a watermelon.
 

Common symptoms

 
Everyone experiences the third trimester and its symptoms differently. Still, you may navigate through the following changes.
 

Constipation

 
The spike in progesterone that relaxes muscles in preparation for labour – as well as the increasing weight of your baby – can lead to constipation in the third trimester (5).
 
Including more fibre-rich foods – fruits, vegetables, whole grains, beans, pulses, legumes, nuts, seeds, and herbs – and drinking plenty of water will aid bowel regularity at this time. Breathing exercises and gentle pregnancy yoga may help, too.
 
You may also want to try Fructo-Oligosaccharides or FOS, derived from the inulin family, which is known to support intestinal health.
 

Heartburn

 
Heartburn and acid reflux often strike in the third trimester due to the hormonal changes that relax the base of the oesophagus (6).
 
Eating little and often, avoiding fatty and spicy foods, and sleeping in a slightly elevated position may provide some relief.
 

Sleep troubles

 
As you approach your third trimester, you may experience insomnia again. Aside from your growing belly, which can make it harder to get comfortable, you may rouse at night to use the bathroom. Of course, feeling anxious and overwhelmed are natural at this stage, too, but these mood changes can often come between you and restful sleep.
 
Following a series of relaxing wind-down rituals, such as light stretching, soaking in a warm Epsom salt bath, or practising breathing exercises, can help you switch off and prepare for bed. Additionally, try to leave enough time between eating and sleeping to prevent heartburn and fullness, which can result in poorer quality rest.
 

Other symptoms

 

• Dizziness

• Feeling hot

• Urine infections

• Acne breakouts

• Thicker, shinier hair

• Backaches

• Shortness of breath

 

What nutrients are important during the third trimester?

 
Owing to your baby’s rapid growth, you need an extra 400 calories in the third trimester. At this stage of pregnancy, you probably feel the urge to indulge. That’s okay – in moderation. However, you still need to prepare your body for the marathon of labour, so focusing on nutritionally balanced meals containing good sources of protein, healthy fats, and complex carbohydrates – along with the following nutrients – is important.
 

Choline

 
Studies suggest maternal choline intake is particularly vital during your third trimester when your baby is growing rapidly and needs more for their development (7).
 
Choline is mainly found in eggs, meat, and seafood, so if your diet doesn’t include these foods – especially if you’re vegan  – it may be worth taking a supplement to cover any shortfalls.
 

Iron

 
Although iron is essential throughout all three trimesters, it plays an especially critical role in the last one. During this stage of pregnancy, your growing baby starts to build up their iron stores to support oxygen transport and muscle development for the first six months of life (8). As such, they need a reliable and consistent supply from your diet.
 
The most bioavailable (readily absorbed) sources of iron include red meat, fish, chicken, and eggs. However, you can also find iron in plant-based sources, like green leafy vegetables, beans, nuts, seeds, and dried fruit.
 
The body can’t absorb iron in plants as efficiently as that in animal products. But eating vitamin C-rich foods (peppers, strawberries, broccoli, Brussels sprouts, and potatoes) simultaneously can support its absorption.
 
Aside from upping dietary iron, you may wish to supplement to stay on top of your intake.
 

Omega-3

 
Omega-3 fatty acids serve as the building blocks of a baby’s brain and retina, especially in the third trimester (9).
 
Eating two portions of oily fish, like salmon, mackerel, and anchovies, every week is an easy way to up your intake of two critical omega-3s: DHA and EPA. Walnuts, chia seeds, flaxseeds, and hempseeds contain ALA – the omega-3 found in plants, which is converted into DHA and EPA in small amounts in the body. Plant-based microalgae is an excellent source of DHA, too.
 
We recommend taking a high-strength fish oil or vegan alternative to support your intake during the third trimester. 
 

Calcium

 
Calcium continues to support the growth of your baby’s bones, teeth, muscles, heart, and nerves in the third trimester (10). If you don’t have enough calcium in your diet, your baby will leach it from your bones, which can make you more vulnerable to osteoporosis.
 
You can find calcium in dairy products (milk, yoghurt and cheese) as well as tofu, leafy greens, almonds, chia seeds, sardines, and lentils. Still, it might be worth including supplemental calcium to cover any shortfalls.
 

Protein

 
Your protein requirements increase in your third trimester – jumping to 50g per day – to support your baby’s growth and build your energy stores for labour (11).
 
Try to include enough protein in every meal and snack. Animal foods like red meat, poultry, dairy, and eggs are great sources of protein, as are plant-based sources, such as nuts, seeds, pulses, legumes, and beans.
 

Remember to take your prenatal multi

 
By the time you reach your third trimester, hopefully, you’re in the swing of taking your prenatal multivitamin. If not, this is a gentle reminder. A high-quality prenatal multivitamin is a simple and convenient way to ensure your growing baby gets everything they need during the last trimester and beyond. 
 

Top tips for the third trimester

 

• Stay active as much as you can, but take it easy as you approach the end of your third trimester. You’ll need all your energy for labour and parent duties.

• Pack every meal with fruit, vegetables, protein, healthy fat, and complex carbs.

• Batch cooking is a great way to stay on top of healthy eating habits after birth. 

• Keep your teeth healthy. Poor dental hygiene may lead to premature labour.

• Stick with your pregnancy multi!

• Drink plenty of water.

 

Find out more

 
If you found this article useful, you can read more about supporting yourself in postpartum, as well as plenty of other helpful guidance on our health blog. Alternatively, please get in touch with our team of expert Nutrition Advisors, who are on hand to provide free, confidential advice.

References:

1. (1) Pregnancy hormones: progesterone, oestrogen and the mood swings NCT. NCT (National Childbirth Trust). Available online: https://www.nct.org.uk/pregnancy/how-you-might-be-feeling/pregnancy-hormones-progesterone-oestrogen-and-mood-swings

2. (2) Pregnancy hormones: progesterone, oestrogen and the mood swings NCT. NCT (National Childbirth Trust). Available online: https://www.nct.org.uk/pregnancy/how-you-might-be-feeling/pregnancy-hormones-progesterone-oestrogen-and-mood-swings

3. (3) Pregnancy hormones: progesterone, oestrogen and the mood swings NCT. NCT (National Childbirth Trust). Available online: https://www.nct.org.uk/pregnancy/how-you-might-be-feeling/pregnancy-hormones-progesterone-oestrogen-and-mood-swings

4. (4) Hormones in labour: oxytocin and the others – how they work. NCT (National Childbirth Trust). Available online: https://www.nct.org.uk/labour-birth/your-guide-labour/hormones-labour-oxytocin-and-others-how-they-work

5. (5) Pregnancy hormones: progesterone, oestrogen and the mood swings NCT. NCT (National Childbirth Trust). Available online: https://www.nct.org.uk/pregnancy/how-you-might-be-feeling/pregnancy-hormones-progesterone-oestrogen-and-mood-swings

6. (6) Pregnancy hormones: progesterone, oestrogen and the mood swings NCT. NCT (National Childbirth Trust). Available online: https://www.nct.org.uk/pregnancy/how-you-might-be-feeling/pregnancy-hormones-progesterone-oestrogen-and-mood-swings

7. Caudill M et al., Maternal choline supplementation during the third trimester of pregnancy improves infant information processing speed: a randomized, double-blind, controlled feeding study. The FASEB Journal. 2018

8. Scholl TO, Maternal iron status: relation to fetal growth, length of gestation, and iron endowment of the neonate. Nutr Rev. 69 Suppl 1(Suppl 1):S23-9. 2011

9. Coletta JM, Bell SJ, Roman AS, Omega-3 Fatty acids and pregnancy. Rev Obstet Gynecol. 3(4):163-71. 2010

10. Kumar A, Kaur S, Calcium: A Nutrient in Pregnancy. J Obstet Gynaecol India. 67(5):313-318. 2017

11. Murphy MM, Higgins KA, Bi X, Barraj LM, Adequacy and Sources of Protein Intake among Pregnant Women in the United States, NHANES 2003-2012. Nutrients. 13(3):795. 2021

 

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