When considering IVF treatment, many people are surprised to learn there are different approaches. Conventional (stimulated) IVF uses medications to produce multiple eggs, while natural cycle IVF works with your body's single naturally selected egg. Each approach has distinct advantages and limitations, and the best choice depends on individual circumstances.
What Is Stimulated IVF?
Stimulated IVF, also called conventional IVF, is the most common form of IVF worldwide. It involves:
- Ovarian stimulation, daily hormone injections (gonadotropins) for approximately 10 to 14 days to stimulate multiple follicles to develop
- Monitoring, regular blood tests and ultrasound scans to track follicle growth
- Trigger injection, to mature the eggs before collection
- Egg collection, typically retrieving 8 to 15 eggs (though this varies significantly)
- Fertilisation and culture, eggs are fertilised and embryos develop in the laboratory
- Embryo transfer or freezing, one embryo is transferred; surplus embryos can be frozen for future use
The aim is to maximise the number of eggs collected, giving more opportunities for fertilisation and embryo development.
What Is Natural Cycle IVF?
Natural cycle IVF works with your body's natural menstrual cycle without (or with minimal) stimulation medications:
- No or minimal medication, relies on the single egg your body naturally selects each month
- Monitoring, ultrasound and blood tests to track the natural follicle development
- Trigger injection, may be used to time egg collection precisely
- Egg collection, retrieval of the single (occasionally two) mature egg
- Fertilisation, the egg is fertilised, and if an embryo develops, it's transferred
A variation called "modified natural cycle IVF" uses a small amount of stimulation to support the natural follicle and prevent premature ovulation.
Comparing the Two Approaches
| Factor | Natural Cycle IVF | Stimulated IVF |
|---|---|---|
| Medications | None or minimal | Daily injections for 10 to 14 days |
| Eggs collected | Usually 1 | Typically 8 to 15 (varies) |
| Cost per cycle | Lower | Higher |
| Success rate per cycle | Lower (7 to 15%) | Higher (30 to 50%+ depending on age) |
| OHSS risk | Essentially zero | Small risk, higher in some patients |
| Embryos to freeze | Rarely | Often possible |
| Can repeat quickly | Yes, consecutive cycles possible | Usually rest between cycles |
Who Might Consider Natural Cycle IVF?
Natural cycle IVF may be appropriate for:
- Women who don't respond well to stimulation, those with low ovarian reserve who produce few eggs even with medications
- Women who want to avoid medications, for personal, medical, or religious reasons
- Those at high risk of OHSS, such as women with polycystic ovary syndrome (PCOS), now officially renamed polyendocrine metabolic ovarian syndrome (PMOS)
- Women with hormone-sensitive conditions, where high oestrogen levels should be avoided
- Couples who prefer a gentler approach, and are willing to accept lower per-cycle success rates
- When cost is a significant factor, though cumulative costs may be similar if multiple cycles are needed
Who Is Better Suited to Stimulated IVF?
Stimulated IVF is generally recommended for:
- Most women undergoing IVF, as it offers higher success rates per cycle
- Women with good ovarian reserve, who are likely to respond well to stimulation
- Those wanting to maximise chances per attempt, particularly given the emotional investment in each cycle
- Women who may want embryos for future use, surplus embryos can be frozen
- When time is a consideration, such as advancing maternal age
Your fertility specialist can help determine which approach is most appropriate based on your individual circumstances, including age, ovarian reserve, and personal preferences.
Understanding Success Rates
When comparing success rates, it's important to consider:
- Per-cycle vs cumulative rates, while natural cycle IVF has lower per-cycle success, multiple cycles may achieve similar cumulative pregnancy rates for some patients
- Cancellation rates, natural cycle IVF has higher cancellation rates (sometimes 15 to 30%) due to premature ovulation or failure to retrieve an egg
- Individual factors, success with either approach depends heavily on age, ovarian reserve, and other fertility factors
Frequently Asked Questions
Is natural cycle IVF less stressful than stimulated IVF?
It can be, as there are no daily injections and fewer side effects from medications. However, the lower success rate per cycle and higher cancellation rate can create their own stress. Each woman experiences this differently.
Can I switch between approaches?
Yes. Some women start with stimulated IVF and move to natural cycle if they respond poorly to medications. Others may try natural cycle first and switch to stimulated IVF if unsuccessful.
Is the egg quality better in natural cycle IVF?
This is often claimed, but evidence is limited. The naturally selected egg isn't necessarily "better" than eggs matured with stimulation. In stimulated cycles, your body would have naturally selected one of those eggs anyway.
Considering IVF Treatment?
If you'd like to discuss which IVF approach might be most suitable for your situation, a consultation can help you understand your options.
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