Natural, Modified Natural and Mild IVF

Mild IVF is a lower-medication approach to in vitro fertilisation. Instead of using higher doses of injectable hormones to produce as many eggs as possible, mild IVF uses oral medication, lower-dose injections, or both to stimulate a smaller group of follicles.

The aim is usually to reduce medication, injections and treatment burden—not necessarily to collect more eggs or achieve a higher success rate in one cycle.

Natural IVF follows the follicle that your body selects naturally during the menstrual cycle. Usually, this means aiming to collect one egg without ovarian-stimulation medication.

A trigger injection may still be used to help time egg maturation and egg collection.

Modified natural IVF follows the naturally selected leading follicle but adds a small amount of medication. The medication may help control the timing of ovulation and, in some cases, allow one or two additional follicles to develop.

The aim is generally to collect one egg, although more may sometimes be obtained.

Mild or natural IVF may be considered for patients who:

• Are expected to produce relatively few eggs even with higher-dose stimulation.

• Have had a previous poor response to conventional IVF.

• Have diminished ovarian reserve.

• Prefer fewer injections or lower medication exposure.

• Want to reduce medication costs per treatment attempt.

• Are concerned about ovarian hyperstimulation syndrome, although modern conventional IVF protocols can also substantially reduce this risk.

• Are comfortable with the possibility of needing more than one egg-collection procedure.

A fertility specialist should assess your age, ovarian reserve, previous treatment response and overall fertility diagnosis before recommending a protocol. Professional guidance is particularly supportive of considering mild stimulation for some patients predicted to be poor responders.

No. Mild or natural IVF is not automatically the best option for every patient.

It may be less suitable when the main priority is to obtain as many eggs or embryos as possible from one retrieval, when several children are desired, or when embryo testing requires a larger group of embryos.

The appropriate approach depends on factors such as age, AMH, antral follicle count, sperm factors, previous IVF results and the number of children desired.

The number of eggs varies from person to person.

• Natural IVF: Usually aims for one egg from the dominant follicle.

• Modified natural IVF: Usually aims for one egg, although additional eggs may sometimes be collected.

• Mild IVF: Aims for a small group of eggs rather than the larger number often targeted with conventional stimulation.

In one study of women with diminished ovarian reserve, mild stimulation resulted in an average of 2.7 eggs compared with 4.8 eggs after conventional stimulation. These figures are from one study and should not be treated as an individual prediction.

Usually, yes. Lower medication exposure generally means that fewer follicles are stimulated, so fewer eggs may be collected.

This can be an acceptable trade-off for someone who is unlikely to produce many eggs with conventional stimulation or who prioritises fewer medications and injections.

Not necessarily. Mild or natural IVF is not designed to guarantee a higher success rate per cycle.

For patients who are capable of producing multiple eggs, collecting fewer eggs may mean fewer embryos and fewer opportunities for transfer. In patients predicted to be poor responders, evidence suggests that pregnancy rates may not be substantially different between mild and conventional stimulation, although evidence regarding live birth rates has been limited.

Your clinic should explain:

• Live-birth rate per started cycle.

• Chance of obtaining an embryo for transfer.

• Cumulative live-birth rate from fresh and frozen transfers.

• Expected number of treatment cycles.

• Total estimated cost over the complete treatment plan.

Yes. Natural IVF is more dependent on the body’s natural timing. A cycle may be cancelled if:

• The follicle does not develop as expected.

• Ovulation occurs before egg collection.

• No egg is retrieved.

• The egg is immature or cannot be fertilised.

• No embryo develops for transfer or freezing.

The possibility of cancellation should be discussed before treatment begins.

Sometimes the follicle contains no egg, the egg cannot be collected, or the egg is immature. This risk is particularly important to discuss when a cycle is designed to produce only one egg.

Your doctor can explain whether another cycle, modified natural IVF, mild IVF or conventional stimulation would be appropriate.

Some patients find mild or natural IVF easier because it may involve fewer injections, lower medication doses and fewer medication-related symptoms.

However, egg collection is still a medical procedure, and patients may experience discomfort, bloating, fatigue or emotional stress. “Mild” refers mainly to the stimulation approach and does not mean that the entire treatment process is risk-free or effortless.

Lower ovarian stimulation generally reduces the risk of ovarian hyperstimulation syndrome, or OHSS. However, the risk is not eliminated.

Modern conventional IVF protocols can also be adjusted to reduce OHSS risk, including individualised medication dosing and appropriate trigger strategies. Your doctor should assess your personal risk rather than choosing a treatment solely because it uses fewer medicines.

There is no reliable IVF protocol that can reverse the age-related decline in egg quality.

Mild or natural IVF may reduce medication exposure and may be a reasonable approach for some patients, but using fewer medicines does not necessarily improve egg quality or embryo quality.

The medication cost for one mild or natural IVF attempt may be lower. However, fewer eggs per cycle can mean that more retrievals are needed.

For this reason, the total cost may be higher or lower depending on:

• The number of retrievals required.

• Medication costs.

• Laboratory and embryo-freezing fees.

• The chance of obtaining an embryo.

• Whether embryo transfer occurs in the same cycle or later.

• The number of children you hope to have.

It is important to compare the estimated total cost and cumulative chance of success, rather than medication cost alone.

There is no standard number of cycles. Some patients may obtain a suitable embryo after one cycle, while others may need several retrievals to build an embryo group.

The likely number of cycles depends on age, ovarian reserve, egg yield, fertilisation rate, embryo development and whether embryo testing is planned.

In many cases, eggs collected through natural or mild IVF can be fertilised using standard IVF or ICSI, depending on the clinical situation.

The recommended fertilisation method depends on factors such as sperm quality, previous fertilisation results and the number of eggs retrieved. Your fertility specialist should explain which method is appropriate for you.

Yes, if suitable embryos develop, they may be frozen for future transfer. The exact options depend on embryo development, clinic policy, legal requirements and whether embryo testing is planned.

Because mild and natural IVF usually produce fewer eggs, there may be fewer embryos available for freezing.

Age remains one of the most important factors affecting egg quality and IVF outcomes.

Mild or natural IVF may be considered for older patients who are expected to produce few eggs, but it cannot eliminate the effect of age on embryo development or miscarriage risk. Your clinic should provide age-specific success rates rather than relying on overall clinic percentages.

Before choosing mild or natural IVF, ask:

• How many eggs are you realistically expecting in my case?

• What is the chance of cycle cancellation?

• What is the chance of retrieving no egg or no mature egg?

• What is the chance of obtaining an embryo for transfer?

• What are your live-birth rates for patients of my age and ovarian-reserve profile?

• What is the estimated cumulative success rate after fresh and frozen transfers?

• How many cycles might I need?

• What is the total expected cost, including medication, retrieval, laboratory work and embryo storage?

• What would be the alternative conventional IVF protocol?

• What would make you recommend changing protocols?