Fresh or Frozen Embryo Transfer: Which Is Best for You?
▫️WRITTEN BY DR RAELIA LEW
One of the most common questions we receive at Women's Health Melbourne is whether a fresh or frozen embryo transfer is better for IVF success. The answer isn't straightforward – and that's actually a good thing, because it means your fertility specialist can tailor the approach specifically to your unique circumstances.
UNDERSTANDING FRESH VS FROZEN EMBRYO TRANSFERS
A fresh embryo transfer occurs when we retrieve your eggs, fertilise them, and transfer the resulting embryo back into your uterus five days later as a blastocyst – all within the same treatment cycle. The embryo has never been frozen; it's transferred in the same cycle it was created.
A frozen embryo transfer involves creating embryos during your IVF cycle, freezing them using advanced vitrification technology, and then transferring them back into your uterus during a separate, menstrual cycle weeks or even months later. The key advantage here is timing – we can prepare your uterine lining under optimal hormonal conditions when it's most receptive to implantation. There are many different methods to prepare your endometrium for embryo transfer. These include using a natural cycle, modified natural cycle, ovulation induction cycle or medicated cycle protocols.
WHY WE SOMETIMES RECOMMEND FROZEN TRANSFERS
MATERNAL SAFETY COMES FIRST
Your safety is always our paramount concern. In some cases, particularly when you've responded very well to stimulation and developed many follicles, there's a risk of ovarian hyperstimulation syndrome (OHSS) – a potentially serious complication that's almost exclusively associated with medications needed to accommodate a fresh embryo transfer. When this risk exists, choosing safer medicines, freezing all embryos and transferring your best embryo in a later cycle is the safest approach.
OPTIMISING THE UTERINE ENVIRONMENT
During a stimulated IVF cycle, we use medications to encourage multiple eggs to develop. While this is excellent for creating embryos, it creates a hormonal environment that's quite different from a natural cycle. These elevated hormones can cause the uterine lining to develop abnormally – sometimes appearing "overripe" with signs of prematurely aging noteworthy under the microscope.
A premature progesterone rise in IVF has been shown in many studies to be associated with much poorer pregnancy rates. In other words, your good embryo could fail because it was transferred in a faulty hormonal environment.
In my practice, I always measure progesterone levels on trigger day when considering a fresh transfer. An early rise in progesterone can actually close the window of implantation, working similarly to emergency contraception by making the lining hostile for successful implantation . When this occurs, even a high-quality embryo may not implant successfully – not because there's anything wrong with the embryo, but because the timing (and the lining) isn't right.
HEALTHIER PREGNANCIES
There's compelling evidence that frozen embryo transfers into an unstimulated, naturally prepared uterine lining are associated with healthier placentas and reduced risks of certain pregnancy complications, including high blood pressure, pre-eclampsia and small-for-gestational-age babies.
WHEN FRESH TRANSFERS MAKE SENSE
Fresh embryo transfers can be ideal for patients with lower ovarian reserve who produce fewer eggs during stimulation. For these patients, the hormonal disruption to the uterine lining is less significant, and avoiding the freeze-thaw process may preserve the best chance for that precious embryo, especially if the embryo itself is unusually fragile.
THE EVOLUTION OF EMBRYO FREEZING
Embryo freezing technology has transformed dramatically over the past 25 years. When I began my fertility training, we used slow-freeze technology and froze embryos at day 2 or 3 when they had only 3-8 cells making them much more vulnerable to the freezing process.
Today, we use vitrification – a rapid snap-freeze technology with cryoprotectants that freeze embryos at the blastocyst stage when they contain approximately 200 cells. This advancement, pioneered by our scientific leaders at Melbourne IVF, means embryos are far more resilient during freezing and thawing. The duration of freezing doesn't affect embryo viability. An embryo frozen for one month has the same potential as one frozen for ten years, provided storage conditions remain optimal.
WHEN TO THINK ABOUT STRATEGIC EMBRYO BANKING
For patients starting IVF in their late 30s or 40s, I often recommend consideration should be given to embryo banking before beginning transfers. The reality is that as a patient and candidate for IVF success, age is an important factor. Compared to your future self, you have the best fertility you'll ever have right now. You have the best egg quality and quantity you'll ever be able to achieve through IVF.
If you want to plan a family and have multiple children, banking embryos from your current cycles may be an excellent strategy. You may require fewer treatments overall and create a better long term prognosis to achieve your family goals. The older you are when undertaking IVF, the more cycles you require to achieve success. Egg quality, embryo quality and egg numbers decline with age, while chromosome errors increase. This might sound sobering, but it's pragmatic. Planning ahead can make all the difference to ultimately achieving your family-building goals.
INDIVIDUALISED DECISION-MAKING
When you look at IVF statistics, you're seeing data for the average patient. Those numbers don't necessarily reflect what's right for your specific circumstances. Your fertility specialist analyses multiple factors including your age, ovarian reserve, response to stimulation, progesterone levels, embryo quality, and family planning goals to determine the optimal strategy for you. This plan may change during your treatment cycle. For example, a plan for fresh embryo transfer may be changed to a “freeze all decision” dynamically, due to observations during your cycle such as a premature rise in progesterone levels.
The question of fresh versus frozen doesn't have a universal answer because the right choice for one person may be different for another. This is why personalised, expert guidance is so important – we're strategising to give each individual embryo its best chance of becoming your baby.
THE BEST OF BOTH WORLDS
There's one scenario I consider the "holy grail" of IVF: warming frozen eggs and transferring a fresh embryo into a natural or modified natural uterine lining. This option is available for women who have previously frozen their eggs and return to use them.
This approach combines the advantages of a fresh embryo and an optimally prepared endometrium in the same menstrual cycle. When warming frozen eggs, I typically recommend warming only enough to create 1-2 embryos for immediate transfer. We know from Melbourne IVF data that twice freezing eggs and embryos can be detrimental to their survival and success rates. We do our best to avoid “double freezing” wherever possible.
YOUR QUESTIONS MATTER
If you're weighing these options, your fertility specialist should explain the rationale behind their recommendations in a way that helps you understand the strategy. While I hope my patients feel informed and empowered, there are situations – particularly concerning safety risks like hyperstimulation – where my clinical experience guides firm recommendations.
After supporting thousands of patients through IVF cycles, I've learned that protecting you from potential complications isn't about limiting your choices – it's about ensuring the safest, most effective path to your goal of having a baby.
At Women's Health Melbourne, we're committed to providing evidence-based, individualised fertility care that considers every aspect of your unique situation. If you'd like to discuss whether fresh or frozen embryo transfer is right for you, I invite you to book a consultation with our team.
Written by Dr Raelia Lew
CREI Fertility Specialist | Director, Women's Health Melbourne & Melbourne IVF
Dr Raelia Lew is the Medical Director of Women’s Health Melbourne. Dr Raelia is a Royal Australia and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) Board Certified CREI Fertility Specialist, and is President Elect of the Australia and New Zealand Society of Reproductive Endocrinologists and Infertility Specialists(ANZSREI).