What to eat for a FET (frozen embryo transfer)
A frozen embryo transfer (FET) is part of the IVF process. It's when an embryo which was previously created and "put on ice" is thawed and placed in the uterus, with the hope that it's going to "stick" and result in a successful pregnancy!
Let's look at some of the nutritional considerations around preparing for a FET.
IVF (in vitro fertilisation) is an assisted reproduction process where eggs and sperm are separately collected, and embryos are then created in a laboratory (by introducing the eggs and sperm to each other to allow for fertilisation to occur).
There are two options after an embryo has been created.
The first option is called a fresh transfer, where an embryo is placed in the uterus a few days after the initial egg collection (usually 3 or 5 days after fertilisation).
The second option is the FET a.k.a. frozen embryo transfer. This is where embryos are initially frozen, and then at a later date, an embryo is selected, thawed, and then placed in the uterus.
Lately I have been asked quite a few times about what to eat when preparing for a FET. I understand why, because it's kind of different to your usual fertility nutrition situation. When it's a FET, we are not looking at egg health or sperm health. The embryo is already in existence!
When preparing for a FET the priority is implantation, which is the process by which the embryo attaches itself to the wall of the uterus (endometrium) and starts burrowing in, and it starts receiving oxygen and nutrients from the mother so that it can grow and develop i.e. the beginning of a clinical pregnancy.
So, the focus of FET preparation is to get the lining of the uterus (endometrial lining) ready to receive an embryo, i.e. full of nutrients and receptive to the incoming embryo. If you have been through the IVF process you will probably know all about your endometrial thickness, because it is typically measured during your regular ultrasounds. The goal is a thick endometrium that is also a receptive endometrium, this requires progesterone.
Foods to support progesterone production
The endometrial lining prepares to receive an embryo in response to the production of progesterone, one of the female sex hormones. Progesterone dominates the second half of our menstrual cycle (post-ovulation), telling our body to prepare the uterus for a possible pregnancy. It makes changes to the uterine lining so that it is receptive to implantation of the embryo.
Let's take a look at some nutrients that can support progesterone production and the foods to find them in.
VITAMIN C: in a study of 150 women with luteal phase defect (a condition usually characterised by low progesterone) vitamin C supplementation was shown to raise progesterone levels (Henmi et al., 2003).
Vitamin C is widely available in many fruits and vegetables. Try: oranges, mandarins, kiwi fruit, strawberries, papaya, capsicum, tomatoes, sweet potato, broccoli, brussels sprouts and potatoes (yes, really, potatoes contain vitamin C!)
VITAMIN B6: this vitamin is involved in making steroid hormones, including progesterone.
Good sources of vitamin B6 include: meat and poultry, some fish (e.g. tuna and salmon), milk, peanuts, soy beans, chickpeas, oats and bananas.
ZINC: zinc is important for the growth and maturation of ovarian follicles, which leads to ovulation. Why are we talking about it when it comes to progesterone, then? Well, in order for your body to make progesterone, you need to ovulate. After ovulation the leftover follicle sac (what the egg is released from) becomes a structure called the corpus luteum, and it's this structure which is responsible for initially secreting progesterone (during pregnancy, the placenta takes over). So, if you want to support progesterone, you've got to support ovulation. There are also some animal studies which suggest that zinc make play a role in endometrial receptivity (how receptive the uterus is to an embryo).
Find zinc in: meat, poultry, shellfish (e.g. crab, prawns, lobster), oysters, eggs, almonds, cashews, pumpkin seeds, hemp seeds and legumes like chickpeas and kidney beans.
Foods to support a thick endometrial lining
Now let's look at a few more nutrients and foods that have been studied with regard to the thickness of the endometrial lining.
As is the case with most fertility nutrition research, there is not a great deal of it and more work is definitely needed!
VITAMIN E: In a study of 103 women undergoing assisted reproduction, supplementing vitamin E increased endometrial thickness (Cicek et al., 2012). Other research has shown that vitamin E may also improve blood flow to the corpus luteum and boost progesterone (Takasaki et al., 2009).
Sources of vitamin E include: nuts and seeds, avocado, spinach and peanut butter.
L-ARGININE: This is an amino acid, which is a component of protein. A very small study of l-arginine supplementation in women with a thin endometrium showed an improvement in thickness in most participants (Takasaki et al., 2010). Similar to vitamin E, l-arginine may also help with blood flow to the corpus luteum and progesterone levels (Takasaki et al., 2009).
L-arginine is found in most protein-rich foods including meat, poultry, seafood, wholegrains, legumes and dairy.
WHOLEGRAINS: In a study of 273 women undergoing IVF, higher wholegrain intake was associated with a higher live birth rate, and this was attributed to increased endometrial thickness and receptivity (Gaskins et al., 2016). Wholegrain foods are full of dietary fibre and nutrients including magnesium, iron, iodine, zinc, B vitamins and vitamin E, so there are many more reasons to include them in your diet!
Try: rolled oats, brown rice, whole grain bread, wholemeal pasta, barley, freekeh, buckwheat and quinoa.
Foods that support your mood and reduce inflammation
During the FET process you also want to make sure you're taking care of yourself. Working on our mood and stress levels may also help with thickening the endometrium and producing progesterone, because this will help to promote reproductive hormone synthesis.
OMEGA 3 FATTY ACIDS: specifically the long chain omega-3 fatty acids EPA and DHA, these offer such a wide array of benefits including for mental health. Higher intakes of EPA/DHA may benefit mood disorders including anxiety and depression (Larrieau & Laye, 2018). In addition to this, these fatty acids are anti-inflammatory which may also help to support implantation (and DHA is essential for baby's brain and eye development).
The best sources of EPA/DHA are your oily fish including salmon, sardines, trout, mackerel and tuna. Aim to include 2-3 servings of fish per week. Not sure which seafood is safe for pregnancy? Check out my article here.
COMPLEX CARBOHYDRATES: high fibre complex carbs keep your blood sugar stable and keep hangry moods and cravings in check during what is usually a pretty emotional time. If you are aiming to eat wholegrains to support your endometrial lining, these are great complex carbohydrates and also have anti-inflammatory benefits, it’s a win, win win.
Think: rolled oats, brown rice, quinoa, barley, whole grain bread, sweet potato, legumes.
One last tip!
In addition to these foods, please don't forget your usual prenatal supplement/s. In particular you want to make sure you are getting your folic acid (or folate) that is very, very important in the earliest stages of pregnancy for reducing the risk of a certain type of birth defect called neural tube defects.
If you are interested in taking supplements which include some of the nutrients discussed above, please first discuss this with your fertility doctor and also consult a qualified nutritionist or dietitian to make sure you are choosing a supplement that is safe and will not negatively interact with your fertility treatment protocol.
Want to do all that you can to support embryo implantation? I dive deep into implantation and share the exact strategies that I use with my 1:1 nutrition clients in my Optimising Implantation Nutrition Guide. This digital guide comes with a 7 day meal plan and recipes to give you lots of practical guidance for boosting your chances of implantation success. Shop the guide HERE (there's an omnivore or a plant-based plan available!).
WHAT TO EAT FOR A FROZEN EMBRYO TRANSFER // Learn about the key nutrients and foods to help prepare for your frozen embryo transfer (FET) with expert fertility nutritionist Monique Cormack. These IVF nutrition tips are specifically to help with progesterone and implantation.