Pregnancy Nutrition – The Third Trimester

First up, a little disclaimer: I am in no way an expert on pregnancy, nor am I a physician or a clinical dietitian. So the information I’m sharing on pregnancy nutrition comes from a combination of information I’ve gleaned over the course of two degrees in nutrition (BSc and MSc), continuing education, and my experiences with my own pregnancies. Please be sure to speak to your health care professional if you have any specific concerns.

Since my own pregnancy is flying along, I thought we had better fit in a third trimester nutrition post before the baby comes and I get sunk into the inevitable newborn bubble.

a sonogram photo and a green smoothie on a grey background

Ladies, the third trimester, ammiright? Ugh! Gone are the golden days of the second trimester, the home stretch is, for many people, a fairly uncomfortable time. That little bub is taking up a lot of valuable real estate in your abdomen, which can bring with it some real nutrition and digestive challenges, including heartburn and constipation.

Although you’re technically eating for two, the other one of you is still on the fairly small size (even though it may not feel that way!), so mammas in the third trimester should aim for roughly an extra 300 calories a day. Of course this totally depends on your genetics, what your activity level is like, how your general health is, and a number of other factors.

Lots of ladies in the third trimester find it tough to eat a large meal, since your stomach is being crowded out by your growing baby. A large meal can also make heart burn and other digestive discomforts worse, so it’s often advisable to aim for several smaller meals per day rather than 2-3 big ones. I also find that eating a light, early dinner tends to mean I sleep better.

If you’re struggling to eat enough due to that cramped stomach space, aim for quality over quantity. That means focusing on nutrient-dense foods that will fill you up with smaller portions, such as healthy fats (think nuts, seeds, avocados, etc), protein (eggs, full-fat dairy, tofu), and complex carbohydrates (beans, legumes, whole grains, fruits, and vegetables).

The better you nourish yourself the better you’ll nourish your growing baby AND prepare your body for the marathon of labour and delivery, and the intensity of the fourth trimester. Focusing on quality nutrient dense foods will help you get through the home stretch with better energy (as good as it gets, ya know?), will help your digestive system to keep working smoothly, and helps to prepare your body for what’s to come.

Important third trimester nutrients:

All of the nutrients we discussed in the second trimester pregnancy nutrition post are still important in the third trimester, but there are some we should be paying particular attention to.

In particular, the fat soluble vitamins A, D, E, and K warrant our attention during this time, and this is due to the fact that fat soluble vitamins are stored in our bodies. Since your body still soon turn it’s attention to the important work of producing breast milk for your baby (it will do this whether you intend to breast feed or not), it’s vital that there is a good store of fat-soluble nutrients to pull from.

Vitamin D

Vitamin D is of particular importance, as vitamin D deficiency in pregnancy puts women at higher risk for preeclampsia (which can suddenly arise in the third trimester), gestational diabetes (should be flagged earlier), and having a low birthweight infant (third trimester).

Good vitamin D stores are also important since it prevents rickets in infants. It’s recommended to supplement exclusively breastfed infants with 400IU of vitamin D per day as most breastmilk is considered to be vitamin D deficient. However, if the mother has good stores and a high daily vitamin D intake herself (of around 6400IU per day), this supplementation may  not be necessary.

Personally, particularly since I live so far north, I like to take the path of ensuring I’ve got adequate vitamin D stores AND providing a daily supplement to my baby.


Anyone else suffer from those horrific toe-curling pregnancy leg cramps that wake you up in the middle of the night?!

Muscle cramps are a good sign you’re not getting enough magnesium in your diet. I’ve had these terrible leg cramps during both of my pregnancies, and as soon as they appeared the second time I started a magnesium supplement. The supplement hasn’t totally eliminated them, but it has reduced both frequency and severity of these leg cramps.

Magnesium supplements and / or adequate dietary magnesium may also reduce the risk of high blood pressure (and therefore preeclampsia) during pregnancy.

If you’re struggling with constipation, a magnesium supplement (specifically magnesium citrate) may help get things moving. However, if constipation is not an issue for you, magnesium glycinate is one of the best absorbed forms along with being the least likely to cause any gastrointestinal side effects. This is the supplement that I’m taking.

Omega-3 fatty acids

Omega-3 fatty acids, and in particular DHA, are vitally important during pregnancy. Throughout pregnancy DHA is incorporated into your baby’s developing brain and eyes, where it helps with the formation of brain cells and is protective of inflammation and damage in the brain.

During the last three months of pregnancy your baby accumulates an average of 67mg of DHA each and every day. Pregnant women should aim to consume at least 300mg of DHA per day, though studies have shown that supplementation with higher levels during late pregnancy results in better coordination and problem solving skills in children tested at 2-4 years of age.

Depending on your diet, it’s totally possible to reach your daily DHA needs from food alone. However, if you, like me, don’t eat fish, you may want to consider supplementation. It’s important to note that plant-based sources of omega-3 fatty acids are typically rich in ALA, which does NOT convert well to DHA in our bodies. So eat all the flax, walnuts, and chia seeds you want, but it’s not going to be enough DHA in the end.

If you’re not eating fatty fish at least 3x per week (I’m not) I recommend that you look into an algae-based DHA supplement. Algae is where the fish get their DHA from in the first place, and is the ONLY reliable plant source of this essential nutrient.

If you’re taking a DHA supplement, ensure that it also contains EPA, another type of omega-3 fatty acid that helps to facilitate transport of DHA across the placenta. I take a daily algae-oil based omega-3 supplement that contains 350mg of DHA and 170mg of EPA.


Yep, those happy bacteria that keep our microbiomes in balance are super important during pregnancy.

For a long time the assumption has been that a baby’s first exposure to bacteria happens during their trip down the birth canal and out the other side. However, newer research suggests that the placenta is actually rich with beneficial bacteria that are transferred to the developing fetus.

Consumption of probiotics and probiotic rich foods during pregnancy has been associated with lower rates of pre-term birth and preeclampsia, which is believed to be due to reduced inflammation in the placenta. Probiotics may also reduce the risk of gestational diabetes, and, in those who do have gestational diabetes, a reduced risk of a very large baby.

Throughout this pregnancy I’ve been participating in a research study to do with maternal bacterial colonies and how they impact fetal outcomes. As a result I’ve been extra conscious of my probiotic intake, mostly through fermented foods and kombucha. I won’t know the results of this study for some time, but I’ll be happy to share them when I do!


Your iron intake is super important in late pregnancy as not only is your baby leeching it from you like a mofo, but blood loss during birth is often substantial and we need adequate iron stores in order to recover. We took a deep dive into iron in the second trimester post, so I’ll direct you back there for more information.

Recommended Reading:

This post really just scratches the surface when it comes to pregnancy nutrition in the third trimester. If you’re interested in learning more, I recommend you check out these sources:

Pregnancy Nutrition – The First Trimester
Pregnancy Nutrition – The Second Trimester
Vegetarian Pregnancy Superfoods – Eggs
What you should know about iron
What you should know about B12

Real Food for Pregnancy by Lily Nichols


Food Heaven Podcast interview with Lily Nichols, RD, author of Real Food for Pregnancy.

This post contains affiliate links, and I may earn a commission at no additional cost to you if you click through and make a purchase. This allows me to continue to provide free content, and I only share products that I use and love myself.


  1. Sustainable Cooks - Sarah says

    You’re so right on the iron intake. I was pretty much licking cast iron in my last two months to keep those iron levels up.

    But, the difference in recovery time between my first and second kiddo is night and day and I think so much of it has to do with all the extra iron.

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