Struggling with low ovarian reserve or poor response to IVF? In this webinar, Dr Elena Santiago, Fertility Specialist at Vida Fertility (Spain), explains how Dual Stimulation (Dual Stim) can dramatically increase egg numbers and improve chances of success — all within a single menstrual cycle. Learn why this method is becoming a game-changer for women over 38, low responders, and anyone needing more embryos for PGT-A.
Dual stimulation, often referred to as “Dual Stim,” is an IVF strategy designed to help patients with low ovarian reserve or poor response to standard stimulation protocols. In this webinar, Dr Elena Santiago, Fertility Specialist at Vida Fertility Institute in Spain, explained how Dual Stim works, which patients may benefit from it, and why it has become a valuable option in selected IVF cases.
The session was hosted as part of an educational series focused on improving IVF outcomes, particularly for patients facing diminished ovarian reserve, advanced maternal age, or repeated low responses to stimulation.
Dr Santiago explained that Dual Stimulation is a protocol involving 2 separate ovarian stimulations within a single menstrual cycle. Each stimulation is followed by its own egg retrieval.
The first stimulation begins in the follicular phase, typically during the first days of menstruation, when a new group of antral follicles is naturally recruited. After the first egg retrieval, a second stimulation starts approximately 5 days later, during the luteal phase, which is after ovulation.
Importantly, Dual Stim does not involve two egg retrievals from one stimulation. Instead, it consists of:
one complete stimulation and egg retrieval in the follicular phase, followed by
a second complete stimulation and egg retrieval in the luteal phase.
Dr Santiago emphasised that the medications used in the second stimulation are often very similar to those used in the first, although adjustments can be made depending on the patient’s initial response.
The rationale behind Dual Stim is based on the understanding that follicular recruitment occurs in multiple waves during a single menstrual cycle.
Dr Santiago explained that, in addition to the well-known follicular wave at the beginning of the cycle, research has shown:
a second wave of follicle recruitment near the end of the follicular phase, before ovulation, and
a third wave occurring during the luteal phase, after ovulation.
Because of these multiple waves, it is possible to stimulate the ovaries effectively even outside the traditional early-cycle window. This biological insight allows clinicians to collect more eggs within a shorter timeframe.
A central part of Dr Santiago’s presentation focused on the impact of age on ovarian reserve and egg quality.
She explained that as women age:
antral follicle count and AMH levels decline,
FSH levels increase as the body attempts to stimulate the ovaries more strongly,
egg quality decreases, and
the probability of chromosomally normal embryos becomes lower.
Dr Santiago noted that from around 38–40 years of age, clinics often recommend PGT-A (preimplantation genetic testing for aneuploidy), although it is not mandatory. At age 40, the chance of having a chromosomally normal embryo is approximately 30%, while after age 43, it falls to below 5%.
By identifying and transferring only chromosomally normal embryos, pregnancy rates per transfer can reach around 65–70%, regardless of age, when a healthy embryo is available.
According to Dr Santiago, Dual Stimulation is particularly suitable for patients who are unlikely to obtain a high number of eggs from a single stimulation cycle.
These include:
patients with low ovarian reserve,
patients who have shown a poor response to previous ovarian stimulation,
patients with reduced egg quality related to age,
patients with a normal ovarian reserve but a low number of blastocysts in prior IVF cycles,
patients planning PGT-A testing, where a higher number of embryos increases the chance of finding a chromosomally normal one.
Dr Santiago explained that IVF success is closely linked to the number of eggs retrieved. While around 15 eggs are associated with optimal live birth rates, many patients with diminished reserve cannot reach this number with one stimulation alone. Dual Stim offers a way to accumulate more eggs and embryos within a single cycle.
Dr Santiago clarified that Dual Stimulation is used only in IVF treatments without fresh embryo transfer.
Because the endometrium is not synchronised after 2 consecutive stimulations, a fresh transfer is not possible. Instead, Dual Stim is combined with:
embryo freezing, often followed by PGT-A testing, or
egg freezing for fertility preservation.
All embryos or eggs are frozen, and embryo transfer is performed in a later, hormonally prepared cycle.
Dr Santiago outlined several advantages of Dual Stim:
By performing two stimulations in one cycle, patients usually obtain more eggs and embryos overall, increasing cumulative pregnancy chances.
For patients undergoing PGT-A, having more embryos significantly increases the likelihood of identifying a chromosomally normal embryo for transfer.
Patients often prefer completing two stimulations in a single four-week period rather than repeating treatments across multiple cycles. This approach is associated with low discontinuation rates.
If the first stimulation yields more eggs or embryos than expected, the second stimulation can be cancelled.
Medication left over from the first stimulation can often be used in the second. Additionally, fewer clinic visits and a single batch of genetic testing for all embryos may reduce overall costs.
Dr Santiago emphasized that studies show:
no differences in fertilization rates,
no reduction in embryo quality,
no increase in chromosomal abnormalities between first and second stimulations.
In some cases, patients even respond better to the second stimulation than to the first.
Dr Santiago described the Dual Stim process in detail.
Patients undergo routine IVF testing, including blood tests, AMH levels, ultrasound with antral follicle count, and genetic testing when indicated. Male partners undergo sperm analysis and genetic testing as required.
Stimulation begins in the early follicular phase. Hormonal injections are self-administered, and follicular development is monitored with ultrasounds and hormone tests. Egg retrieval is performed under light sedation approximately 36 hours after the trigger injection.
After the first retrieval, fertilisation and early embryo development are assessed. Based on the results, patients decide whether to proceed with the second stimulation.
About 5 days after the first retrieval, a second stimulation begins. Ovaries may appear enlarged during the first cycle, which is normal. Monitoring continues, and stimulation may last slightly longer, sometimes up to 16 days.
Once follicles are mature, a second trigger is given and a second egg retrieval is performed.
Dr Santiago shared that in many cases where the first stimulation produced few or no embryos, the second stimulation resulted in improved outcomes, sometimes producing embryos when the first did not.
Before starting the second stimulation, clinicians ensure:
ovaries are not excessively enlarged,
there is no significant free fluid,
the patient feels well,
there are no signs of ovarian hyperstimulation syndrome.
If any concerns arise, treatment is paused and resumed later if appropriate.
Dr Santiago concluded that Dual Stimulation is a valuable and evidence-based strategy for selected patients. It is particularly useful for:
low ovarian reserve,
poor responders,
patients requiring embryo accumulation for PGT-A,
fertility preservation cases.
Dual Stim does not compromise egg or embryo quality and is generally well accepted by patients. By increasing the number of eggs and embryos obtained in a short timeframe, it can significantly improve the chances of IVF success for patients who might otherwise have limited options.
Dual Stimulation combines 2 ovarian stimulations within the same menstrual cycle. The aim is to obtain a higher number of eggs in a shorter period of time. By doing 2 stimulations in 1 cycle, we can increase the total number of eggs and embryos, which ultimately increases the chances of success.
A conventional IVF cycle usually lasts around 2 weeks. With Dual Stimulation, there is an additional period of approximately 5 days between the first egg retrieval and the start of the second stimulation. In total, Dual Stim takes around 5 weeks of treatment. It does take longer, but for many patients it is worth it.
Dual Stimulation allows us to accumulate more embryos, especially in patients over 40 who wish to undergo IVF with their own eggs and already have low ovarian reserve.
Instead of obtaining only one or two embryos from a single stimulation, we can perform two stimulations in the same cycle and potentially achieve 2 to 4 embryos. This increases the chances of finding a healthy embryo, which is important because the probability of a chromosomally normal embryo is usually low in these patients. We generally need several embryos to obtain at least one healthy 1.
Many of the patients we recommend Dual Stimulation to have already undergone several IVF cycles, so they are familiar with the process. Others see it as an opportunity to do 2 cycles in one and see what happens before considering other options.
It involves putting all efforts together—emotional, physical, and economic—at the same time to achieve the best possible result. In some cases, the first stimulation does not produce eggs or embryos, but the second stimulation does. This gives patients an additional opportunity to obtain a good outcome.
A common misconception is that follicles that did not grow during the first stimulation will grow during the second. This is not correct. The second stimulation acts on completely new antral follicles that appear after ovulation.
Another misconception is that we selectively aspirate only large follicles during the first retrieval to leave smaller ones for the second. This is not the case. We aspirate all follicles during the first retrieval. New follicles will appear after ovulation and will be stimulated during the second phase.
Low ovarian reserve is one of the most limiting factors in reproductive medicine. Research is ongoing, but egg quality remains the most important factor. Sometimes one good egg is enough for a pregnancy, but in most cases, having several eggs improves the chances of obtaining at least one good embryo.
For patients with low ovarian reserve, add-on strategies such as Dual Stimulation can make a meaningful difference.
This is not a typical case where we would recommend Dual Stimulation from the start. The first step would be to assess the response to an initial stimulation. If a good number of eggs—more than 8—are obtained and good-quality embryos are achieved, Dual Stimulation may not be necessary.
If the response is poor or the embryo quality is low, then Dual Stimulation could be considered as a second step.
This is a common concern, but in most patients, we actually see an equal or even better response during the second stimulation. The most difficult aspect is emotional and physical fatigue over several weeks.
Physically, the ovaries recover quickly after the first retrieval. New follicles begin to grow soon after. We only avoid the second stimulation if there is a very strong response to the first cycle with significant discomfort or risk of ovarian hyperstimulation.
There are several waves of antral follicle development during one menstrual cycle—at least 3. After ovulation, a completely new wave of follicles appears. These are the follicles stimulated during the second phase.
Aspirating follicles during the first retrieval, even small ones, does not affect the second stimulation.
It is similar to conventional IVF. Follicles measuring around 16–18 mm are usually mature, with a maximum size of approximately 22–24 mm.
Yes, this is very common for patients living abroad. We advise resting on the day of the egg retrieval, but travelling the following day is not a problem. Patients can have ultrasound scans in their home country and start the second stimulation there before returning for the second retrieval.
Yes, we have used Dual Stimulation in patients up to this age. However, age is not the only factor. Egg quality is critical, and achieving eggs or embryos can be very difficult at this stage. Dual Stimulation can be attempted, but if it does not work, other options should be discussed.
There is no need to thaw and refreeze embryos. When an embryo reaches the blastocyst stage on day five or six, we perform the biopsy and then freeze the embryo. The biopsy samples can be stored while waiting for embryos from the second stimulation.
All biopsy samples are then sent together to the genetic laboratory. This approach does not increase stress on the embryos.
We currently use standard biopsy-based PGT-A. We have strong expertise in this technique, and embryos tolerate it well at the blastocyst stage. Survival rates after thawing are very high.
Non-invasive PGT-A is still considered experimental, and results are less reliable. For now, a biopsy provides more accurate information about an embryo’s chromosomes.
It depends on ovarian reserve. If ovarian reserve is good and we expect a strong response with at least eight eggs, Dual Stimulation may not be needed. However, in most cases at this age, ovarian reserve is low. In those situations, Dual Stimulation is usually recommended to increase the number of embryos and the chance of finding a healthy one.
