Nalini Mahajan1 and Shivani Singh2
(1)
Department of Reproductive Medicine, Nova IVI Fertility, B 2/1a, Safdarjung Enclave, Africa Avenue, New Delhi, Delhi, 110029, India
(2)
Department of Reproductive Medicine, Srijan Fertility, Janka Puri, New Delhi, Delhi, India
Nalini Mahajan
Email: nalinimahajan@hotmail.com
Abstract
More than three decades of COH for in vitro fertilization have exposed us to its various shortcomings like higher incidence of chromosomal abnormalities, high cost, low compliance and limited results in POR, and side effects like OHSS and higher-order multiple pregnancies. In order to overcome these problems associated with conventional stimulation protocols, ISMAAR has proposed mild stimulation whose aim is to limit the number of oocytes obtained to less than eight by the administration of low doses or fewer days of exogenous gonadotrophins in GnRH antagonist co-treated cycles or use of oral compounds (like antiestrogens or aromatase inhibitors) with or without gonadotrophins with antagonist co-treatment for ovarian stimulation. Many have proposed natural and modified natural cycle IVF, especially for women with poor ovarian reserves.
Mild stimulation entails decreased dose of gonadotrophins, decreased days of injections, reduced chances of OHSS, equivalent CPR, decreased aneuploidy rate, better endometrial receptivity, lower rate of HOMP, and overall lower per cycle cost because of lower drug cost and delivery of singletons. On the other hand, there are distinct disadvantages: a decreased number of oocytes are recovered, no or few embryos are available for cryopreservation, and ultimately cost, physical, and psychological burden may go up because of repeat fresh cycles.
Keywords
Mild IVFConventional IVFNatural cycle IVFModified natural cycle IVFISMAAR
12.1 Introduction
The advent of IVF saw oocyte retrieval from a single follicle in a natural cycle. The disadvantages of having only one oocyte to work with lead to the introduction of ovarian stimulation (OS) for IVF. More oocytes meant more embryos which offered the possibility of embryo selection; this in turn helped to improve pregnancy rates – ART had finally taken a step forward.
Three seminal events changed the course of IVF: introduction of gonadotrophins which increased oocyte yield, GnRH agonist to prevent the premature LH surge, and availability of cryopreservation to freeze supernumerary embryos. Availability of cryopreservation initiated a trend to maximize the number of oocytes through hyperstimulation of the ovaries. Unfortunately this leads to the ovarian hyperstimulation syndrome (OHSS) which increased patient morbidity and mortality. Cycle programming to ease out the work schedule of physicians and embryologists added to the physical burden of treatment. Contraceptive pills given in the previous cycle and agonist injections continued till timing are convenient for the clinic, lead to increased requirement of gonadotrophins, and probably compromise the reproductive performance [1].
Today the pendulum has started swinging back. Problems associated with OHSS, complex and expensive protocols, weeks of daily injections, and the resultant high drop-out rate forced physicians to rethink their stand on OS protocols. Additionally improved laboratory conditions and culture media have reduced the need for a large number of oocytes. Edwards et al. in 1996 were the first to advocate milder stimulation for IVF [2]. Advent of GnRH antagonist paved the way for development of more patient-friendly protocols which involved mild stimulation. The aim of mild protocols is to reduced treatment burden without compromising the pregnancy rate.
Introduction of a new concept does not gain immediate acceptance – there always are proponents and opponents. This article aims to examine the pros and cons of the process. The decision to adopt either rests with the treating physician based on the evidence presented.
12.2 Definition
Over the years there have been no well-defined criteria to define mild stimulation, in fact even the terminology has been varied with terms such as soft, gentle, minimal, mild stimulation being used when a deviation was made from the standard stimulation protocol. This leads to the formation of “ISMAAR” (International Society for Mild Approaches in Assisted Reproduction), which aimed to clearly define the various non-conventional stimulation protocols [3] (Table 12.1).
Table 12.1
ISMAAR terminology with protocols
|
Recommended |
To replace |
Aim |
Protocol |
|
Natural cycle IVF |
Unstimulated IVF Spontaneous cycle IVF |
Single oocyte |
No medication |
|
Modified natural cycle IVF |
Seminatural IVF Controlled Natural IVF |
Single oocyte |
hCG only GnRH antagonist and FSH/HMG add back |
|
Mild IVF |
Soft stimulation IVF Minimal stimulation IVF Friendly IVF |
2–7 oocytes |
Low dose FSH/HMG, oral compounds and GnRH antagonist |
|
Conventional IVF |
Standard IVF Routine IVF Controlled ovarian stimulation IVF |
≥8 oocytes |
GnRH agonist or antagonist along with conventional FSH/HMG dose |
From Nargunde et al. [3]
Mild IVF stimulation is defined by ISMAAR as the administration of:
1.
2.
The aim of mild stimulation is to limit the number of oocytes obtained to less than eight.
12.3 Mild Stimulation Protocol
The concept of “FSH Threshold” and “FSH Window” forms the basis of all our stimulation protocols. FSH threshold being the level of FSH required to initiate follicular growth and FSH window is the time frame for which this FSH level plateau’s to obtain cohort recruitment. Drop in FSH levels following rise in estradiol level is responsible for selection of the dominant follicle. It follows then that the wider the FSH window, the more the follicles recruited [4]. Thus, in conventional IVF, multifollicular recruitment is achieved by administering a high dose of gonadotrophins for a longer duration; thus keeping the FSH window open for a longer time. In mild IVF a moderate elevation is sought since the aim is to have a small cohort of follicles; hence, the gonadotrophin dose is reduced. In the conventional protocol, follicular recruitment is totally dependent on exogenous FSH since the pituitary is downregulated. In the mild stimulation protocol, on the other hand, initial recruitment is by the endogenous FSH rise in the late luteal phase. Exogenous FSH added subsequently (cycle days (CD) 2–5) prevents decrease of FSH levels inducing multifollicular development by preventing follicular dominance [5].
12.3.1 Drugs Used for Ovarian Stimulation (OS) in “Mild Stimulation Protocol”
Both oral and injectable ovarian-stimulating agents can be used since the pituitary is not downregulated. The drugs used are:
1.
2.
3.
12.3.1.1 Gonadotrophins
Gonadotrophins with or without oral ovulogens still remain the mainstay of OS. The choice between recombinant and urinary drugs is a question of availability and economics since it has been shown unequivocally that there is no difference in outcome [6].
Dose of Gonadotrophin
The dose of gonadotrophin is kept at 75–150 IU starting from days 2–5 of the cycle. A fixed daily dose of 150 IU rFSH compared with 100 IU/day was found to be more effective in inducing multifollicular growth when ovarian stimulation was started on CD5 [7]. The starting dose of gonadotrophin in the conventional protocol varies between 225 and 300 IU though it may be lower in PCOS patients.
Day of Starting Stimulation
Gonadotrophin administration can be initiated from cycle days (CD) 2–5 in the mild protocol, while it starts from CD2 in the conventional protocol. A cancellation rate of almost 15–20 % is observed when starting from CD5 because of mono- or bifollicular response. Starting on CD2 allows for more follicles to be recruited. De Jong et al. suggested that ovarian stimulation could be initiated as late as CD7 [7]; however, the number of women showing multifollicular development with this protocol was lower than with those starting stimulation on CD2–5 [8], and it never became popular.
12.3.1.2 Clomiphene Citrate (CC)
CC is an antiestrogen and has been used very successfully in ovulation induction for many decades. Trounson et al. were the first to use CC for OS in IVF in 1981 [9]. Once gonadotrophins were introduced they replaced CC as they were far more effective in getting a multifollicular response. Introduction of GnRH agonist for pituitary downregulation in IVF protocols spelt a death knell for CC since CC needs an intact hypothalamo-pituitary-ovarian axis for its action. The reintroduction of this antiestrogen came about with the use of antagonist in IVF. Addition of CC reduces the dose of gonadotrophin required for stimulation [10], thereby reducing the cost of the IVF cycle. The dose used is 50–100 mg for 5 days from cycle day 2 along with 150 IU of gonadotrophin. The dose of CC has not been standardized. CC can be used by itself as well; however, the number of follicles recruited is lower, and its antiestrogenic effects can be detrimental to implantation.
12.3.1.3 Aromatase Inhibitors (AI)
AIs inhibit the aromatization of androgens to estrogens thereby providing a negative feedback to the pituitary. In addition, the increased intraovarian androgens increase the sensitivity of the antral follicles to FSH [11] and may increase the number of pre-antral and antral follicles [12]. Advantage over clomiphene is thus twofold – no antiestrogenic effect on the endometrium and no depletion of E2 receptors [13] and an improvement of antral follicle sensitivity to FSH thus improving recruitment. The dose varies from 2.5 to 5 mg daily for 5 days starting from cycle day 2 and is administered orally.
AIs have been used with gonadotrophins extensively in poor responders and patients requiring fertility preservation as it keeps the E2 levels low. At present letrozole is an off-label drug, and its use as an ovulation induction agent is banned in India due to concerns about teratogenicity.
12.3.2 Preventing the Premature LH Surge
GnRH analogs are used in IVF to prevent the premature LH surge. The agonist has been in use for more than 20 years, and after many years of experience, it has been established that the long downregulation regime gives the best results in IVF. The antagonist was introduced in 2000 and after some initial hiccups is slowly gaining ground.
12.3.2.1 GnRH Antagonist
GnRH antagonists prevent the premature LH rise by competitive binding to the pituitary GnRH receptor. This leads to an immediate suppression of gonadotrophin secretion. Unlike the GnRH agonists, they do not cause an initial flare of FSH and LH, and there is rapid recovery of pituitary action once the effect wears off in 24 h.
GnRH antagonist is typically started as a daily injection of 0.25 mg administered s/c, in a fixed protocol from CD5/6 or a flexible protocol when the follicle size is between 12 and 14 mm and E2 >200 pgm/ml/. This allows the use of endogenous FSH action for initial follicular growth and helps to reduce the dose of gonadotrophins. It is also given as a single dose of 3 mg s/c, but this is not available in India.
The advent of GnRH antagonists with its rapid and reversible action brought to fore a surge of protocols using oral and a combination of oral and injectable ovarian-stimulating agents. These protocols helped to reduce the physical and financial burden of ART treatment. The introduction of antagonist protocols was met with a lot of skepticism since they were reported to give lower pregnancy rates [14]. The ease of administration and reduced medication used in patient especially one’s with poor ovarian reserve overrode these concerns, and as experience grew with the drug, claims of lower pregnancy rates were nullified [15]. Antagonist protocols using gonadotrophin only and a combination of clomiphene citrate/letrozole with gonadotrophins are popular for mild stimulation IVF.
12.3.2.2 GnRH Agonist
Long downregulation protocol involves starting GnRH agonist in the luteal phase of the previous cycle. This protocol is the most favored IVF protocols. Deep suppression of the pituitary necessitates the use of heavy doses of gonadotrophins for ovarian stimulation. So mild stimulation protocols cannot be used effectively with agonist suppression. GnRH acts by receptor depletion, and hence there is an initial gonadotrophin flare from the pituitary. Protocols using this action of the agonist are called “agonist flare protocols.”
Two major problems associated with agonist suppression are the need for higher doses of gonadotrophin with a consequent increase in the chances of hyperstimulation and almost 21 days of agonist injection.
12.3.3 Implications of Mild Stimulation IVF
Acceptance of any IVF protocol is intimately connected to the pregnancy rate and live birth rate achieved. This, in turn, would depend on the oocyte and embryo quality and alterations in endometrial receptivity. Physical and emotional burdens of a regime also play an important role.
Van der Gaast et al. have shown that the ideal number of oocytes after a conventional long protocol is 13 [16]. When the number is lower or higher, the pregnancy rate is compromised. In this context, aiming for a lower number of oocytes would seem both contradictory and counterproductive. The reduction in complications reduced physical and emotional burden, and the reasonable pregnancy rates achieved with mild stimulation have obligated physicians to consider this approach to improve patient experience. Reduced oocyte numbers obtained through mild stimulation appear to differ from reduced numbers obtained in the conventional regime. It appears that poor oocyte yield after classical ovarian stimulation probably reflects a poor ovarian response to FSH and that is associated with poor IVF outcome. However, low number of oocytes after mild stimulation probably represents a “quality selection,” i.e. stimulation of only the most mature follicles which result in high-quality embryos and in a pregnancy.
12.3.4 Comparison of Pregnancy Rates
Studies have compared the success rate of mild vs. standard ovarian stimulation in women with normal and poor ovarian reserve. In fact the advantage of mild stimulation was first recognized in poor responders.
12.3.4.1 PR in Women with Normal Ovarian Reserve
Three RCTs compared mild with the classical stimulation regimen. Pooled data showed an ongoing pregnancy rate per started cycle of 15 % in the mild group and 29 % in the conventional group showing that mild stimulation is not as effective as the conventional strategy [17]. Freeze-thaw cycles were not included in these studies. Inclusion of freeze-thaw cycles would improve the CPR (cumulative pregnancy rate) in the conventional group, as cycles with mild stimulation may not generate supernumerary embryos.
Of the three RCTs, the first by Hohmann et al. [18] included 142 normal responders who were divided into three groups: group A, long downregulation protocol, and groups B and C, antagonist protocol. In group B stimulation was started on CD2, and in group C it was started on CD5. Gonadotrophin dose was 150 IU. There were no differences in PR between the three groups though women in group C had a higher cancellation rate because of insufficient response.
Baart et al. [19] compared mild protocol with the conventional long downregulation protocol in 111patients. A dose of 150 IU of rFSH was started from CD5 in the mild group and 225 IU in the long protocol. The ongoing pregnancy rate per started cycle was 21 % in the “mild” group and 18 % in the control group, which was not statistically significant. PGS was performed on these embryos, and there were fewer numbers of aneuploid embryos in the mild stimulation group.
The largest RCT by Heijnen et al. [20] included 404 women who had approximately 800 cycles. In this study, the group with mild stimulation had a selected single embryo transfer, while the conventional group had two embryos transferred. The number of oocytes retrieved was lower, and the pregnancy rate per cycle was significantly lower in the “mild” stimulation group (17.6 % vs. 28.6 %, p < 0.0001). The patients however tolerated this protocol better, and the rate of discontinuation of treatment was lower. The cumulative live birth rate after 1 year of IVF treatments was comparable in the two groups (43.4 % with mild protocol, 44.7 % with the conventional regimen); the twinning rate was also significantly lower in the “mild” stimulation-SSET transfer group (0.5 % vs. 13.1 %, p < 0.0001). According to the authors, a reduced chance of birth per cycle in the “mild” regimen might be compensated by the increased number of IVF attempts in a fixed time.
Ovarian aging, ovarian reserve, and high BMI predict the risk of insufficient response to “mild” stimulation, and a predictive model has been developed in order to minimize the need of cancelling [21].
12.3.4.2 Women with Poor Ovarian Reserve
OS of women with poor ovarian reserve is beset with problems and frustration. Despite high doses of gonadotrophins, oocyte yield remains poor, and cancellations are high. It has been the trend to use doses as high as 600 IU to achieve good follicular recruitment. Unfortunately such strategies have not proven very useful [22] primarily because you cannot force out of a bank what it does not have. The poor pregnancy rates cannot justify the greatly increased cost of medicine; hence, there has been a shift toward mild stimulation.
Land et al. [23] observed that the IVF outcome of patients given a starting dose of 225 FSH UI/day vs. those receiving 450 UI/day was similar, even though more oocytes were obtained with the higher dose. High gonadotrophin dosage may prevent cycle cancellation but provides no advantage in terms of pregnancy rate, live birth rate, or miscarriage rate. It is believed that high doses of FSH recruit “resistant” follicles rescuing them from atresia, but the oocytes that they host are of poor quality and usually do not result in the generation of good quality embryos [24].
CC/Gonadotrophin/Antagonist Regimes
Reduce the cost and physical burden of treatment. In most studies, gonadotrophins 150/225 IU are combined with CC in a dose of 50–100 mg/day for 5 days from cycle day 2, during the early follicular phase. Unfortunately there is a high rate of heterogeneity in studies.
Two randomized trials that compared CC/HMG antagonist protocol to conventional agonist protocol came up with contradictory results. In the study by Dhont et al. [25], there was a significantly higher cycle cancellation rates and lower pregnancy rates per cycle (p = 0.002). The study by Lin et al. [26] concluded that PRs were similar in the two protocols, gonadotrophin used and number of stimulation days, and a number of oocytes retrieved were lower in the CC group. A similar outcome was achieved by other authors in retrospective studies.
Aromatase Inhibitors
Aromatase inhibitors are administered orally and help to reduce the cost of treatment by reducing the requirement of gonadotrophins, especially in patients with poor ovarian reserve. Grabia et al. [27] observed a PR of 27 % in good prognosis patients. Most studies have used letrozole with the standard dose of gonadotrophins in antagonist protocols. Verpoest et al. [28] randomized 20 good prognosis patients for the use of 150 IU rFSH from CD2 with or without the addition of 2.5 mg letrozole. GnRH antagonist co-treatment was started from CD6. The use of aromatase inhibitors resulted in higher numbers of oocytes and a tendency toward higher clinical pregnancy rates per started cycle in the letrozole group.
In conclusion oral ovulogens in combination with gonadotrophins have a place in cost-effective mild ovarian stimulation treatments especially in poor responders. More RCTs however are needed to assess the true benefit of these protocols.
12.3.5 Comparison of Embryo Quality
High estradiol levels have a negative impact on the developmental and implantation potential of embryos [29]. An increase in aneuploid embryos has also been reported [30]. It has been hypothesized that ovarian stimulation might disrupt mechanisms involved in maintaining accurate chromosome segregation [31]. Baart et al. [19] found a higher number of aneuploid embryos in the conventional protocol suggesting that more oocytes do not necessarily mean more good quality or more chromosomally normal oocytes. These findings imply that mild stimulation selects less oocytes but with a better quality that lead to the production of euploid embryos.
12.3.6 Comparison of Endometrial Receptivity
Supraphysiological levels of estradiol negatively impact endometrial receptivity [32] and are responsible for implantation failure. This point has been amply proved by the higher pregnancy rates in oocyte donation cycles where the endometrium is not subject to high steroids. Global gene profiling of the endometrium has revealed that there are alterations in the endometrial gene profiles during the phase of receptivity, in patients who have undergone stimulation [33]. The comparisons of gene expression from the same patients between natural and stimulated cycles revealed that endometrial profiles showed moderately altered receptivity in most cases (86 %) and a strongly altered receptivity in14 % during COS [34]. Mild stimulation protocols aim at a more physiological response and hence would improve implantation rates [35]. Between agonist and antagonist, the endometrial gene expression pattern is closer to the natural cycle in the GnRH antagonists protocols [36].
12.3.7 Psychological Aspects
Couples faced with infertility are under immense emotional stress, which is compounded by the stress-related to treatment. Patients are on an emotional roller coaster oscillating between hope, anxiety, and bitter disappointment cycle after cycle. With respect to treatment failure, patients have symptoms of depression, anger, and guilt; psychological stress is the most important reason for patients to discontinue treatment [37].
Mild stimulation protocols have fewer symptoms of depression after IVF failure, the drop-out rate is lower, and patients go for repeat cycles earlier, thus improving their CPR [38–40]. However, lower per cycle pregnancy rates and repeated IVF attempts by themselves would increase stress. Devroy et al. [41] failed to observe a difference in anxiety levels or depression between patients in the mild and conventional protocol. So far there is inconclusive evidence to confirm a psychological benefit with mild protocols.
12.3.8 Cost Comparison
Cost per cycle is lower in the mild stimulation protocol, but since more fresh attempts are required to achieve pregnancy, the cost evens out. Cost of antagonist is still much higher than agonist. There is however an overall reduced cost till delivery because of the reduction in multiple pregnancies [42]. Low cycle cost may provide accessibility to patients in the lower socioeconomic strata giving them an opportunity to have at least one cycle.
12.3.9 Physical Burden
Reduction in the days and number of injections, reduced visits for monitoring, reduced blood tests, and finally a reduction in OHSS [20] dramatically alleviate the physical burden of treatment in mild protocols. Long-term health risks related to excessive ovarian stimulation need to be kept in mind though so far studies on this front have been reassuring.
Listed below are the advantages and disadvantages of “mild stimulation IVF.”
12.3.10 Advantages
1.
2.
3.
4.
5.
6.
7.
8.
12.3.11 Disadvantages
1.
2.
3.
4.
5.
12.4 Natural Cycle and Modified Natural Cycle IVF
12.4.1 Natural Cycle IVF
Natural cycle IVF consists of simply monitoring the spontaneous cycle and retrieving a single oocyte post the spontaneous LH surge. Natural cycle IVF is more patient friendly in terms of requirement of no or far less hormonal medication, but needs more intense cycle monitoring and LH surge monitoring on the part of treating physician and round the clock working embryology laboratory. The per cycle costs of natural cycle IVF have been calculated to be 20–25 % of those of stimulated IVF [43]. Ongoing pregnancy rates per started natural cycle IVF have been reported to be dismal 7.2 % only.
12.4.2 Modified Natural Cycle (MNC-IVF)
To improve outcomes while preserving the advantages of natural cycle IVF, modifications have been made. In the “modified” natural cycle (MNC-IVF), rather than waiting for the spontaneous LH surge, inj. Hcg is given once the diameter of the leading follicle reaches 17–18 mm. To prevent the occurrence of a premature LH rise, which is seen in as many as 20 % of cycles, some protocols in MNC-IVF use GnRH antagonist during the late follicular phase. The ongoing growth of the dominant follicle is supported by the addition of exogenous gonadotrophins (referred to as “add back”). In most studies, GnRH antagonist and gonadotrophins (75–150 IU/day) are initiated at a follicle diameter of 12–17 mm.
Promoters of natural cycle IVF offer it as a series of treatment cycles, for it is safer, less stressful compared with conventional stimulation. It has been postulated that after four cycles of natural cycle IVF, the cumulative pregnancy rates are as high as 46 % with an associated live birth rate of 32 % in selected groups of patients [44]. Even though four cycles of natural cycle IVF were found to be comparable to a single cycle of conventional IVF in terms of pregnancy rates and cost effectiveness, the added investment of time and increased number of oocyte retrieval procedures also should be taken into account.
Most studies regarding modified natural cycle IVF include patients with a previous poor response to conventional ovarian stimulation. In this population, success rates between 0 and 14 % per started cycle have been reported in nonrandomized studies [45–47]. One large cohort study analyzed the cumulative pregnancy rate after three modified natural IVF cycles in good prognosis patients [48]. The ongoing pregnancy rate per cycle was 8.3 and 20.8 % after up to three cycles.
Conclusion
IVF is an ever evolving technology. There has been a sea change in technique both in the clinic and the laboratory and an improvement in drug quality and mode of administration. Despite these changes, there is still an immense physical and emotional burden attached to treatment. The treatment involves daily injections, frequent ultrasounds and blood tests, and anesthesia general or local, for oocyte retrieval. Among the complications, the most terrifying one is ovarian hyperstimulation syndrome which can be life threatening.
Mild stimulation protocols resulted from a desire to make the procedure more safe and simple. The fact that there has been an immense improvement in the IVF laboratory gave courage to the physician to aim for less eggs reducing the dose of gonadotrophins required and consequently the cost and complications. Unfortunately the change was not universally accepted because the per cycle pregnancy rates are lower, and the cumulative pregnancy rate though projected to be similar takes many more cycles of stimulation since there are less embryos available for cryopreservation. The cost too though low per cycle ultimately levels out.
The social scenario is also changing with more and more older women coming for IVF. Studies comparing the two protocols specifically in women over 38 years are not available, and more are required even in the younger age group. The contention that the emotional distress is lower has also been challenged. The decision to use either protocol has to be based on physician discretion and patient acceptance after full information of the pros and cons; the future may well be different.
References
1.
Griesinger G, Kolibianakis EM, Venetis C, Diedrich K, Tarlatzis B. Oral contraceptive pretreatment significantly reduces ongoing pregnancy likelihood in gonadotropin-releasing hormone antagonist cycles: an updated meta-analysis. Fertil Steril. 2010;94(6):2382–4.CrossRefPubMed
2.
Edwards RG, Lobo R, Bouchard P. Time to revolutionize ovarian stimulation. Hum Reprod. 1996;11(5):917–9.CrossRefPubMed
3.
Nargund G, Fauser BC, Macklon NS, Ombelet W, Nygren K, Frydman R; Rotterdam ISMAAR Consensus Group on Terminology for Ovarian Stimulation for IVF. The ISMAAR proposal on terminology for ovarian stimulation for IVF. Hum Reprod. 2007;22(11):2801–4.
4.
Macklon NS, Stouffer RL, Giudice LC, Fauser BC. The science behind 25 years of ovarian stimulation for in vitro fertilization. Endocr Rev. 2006;27(2):170–207.CrossRefPubMed
5.
Verberg MFG, Eijkemans MJC, Macklon NS, Heijen EMEW, Baart EB, Hohmann FP, et al. The clinical significance of the retrieval of a low number of oocytes following mild ovarian stimulation for IVF: a meta-analysis. Hum Reprod Update. 2009;15(1):5–12.CrossRefPubMed
6.
van Wely M, Kwan I, Burt AL, Thomas J, Vail A, Van der Veen F, Al-Inany HG. Recombinant versus urinary gonadotrophin for ovarian stimulation in assisted reproductive technology. Cochrane Database Syst Rev. 2011;(2):CD005354.
7.
de Jong D, Macklon NS, Fauser BC. A pilot study involving minimal ovarian stimulation for in vitro fertilization: extending the ‘follicle-stimulating hormone window’ combined with the gonadotropin-releasing hormone antagonist cetrorelix. Fertil Steril. 2000;73(5):1051–4.CrossRefPubMed
8.
Hohmann FP, Laven JS, de Jong FH, Eijkemans MJ, Fauser BC. Low-dose exogenous FSH initiated during the early, mid or late follicular phase can induce multiple dominant follicle development. Hum Reprod. 2001;16(5):846–54.CrossRefPubMed
9.
Trounson AO, Leeton JF, Wood C, Webb J, Wood J. Pregnancies in humans by fertilization in vitro and embryo transfer in the controlled ovulatory cycle. Science. 1981;212(4495):681–2.CrossRefPubMed
10.
Weigert M, Krischker U, Pohl M, Poschalko G, Kindermann C, Feichtinger W. Comparison of stimulation with clomiphene citrate in combination with recombinant follicle-stimulating hormone and recombinant luteinizing hormone to stimulation with a gonadotropin-releasing hormone agonist protocol: a prospective, randomized study. Fertil Steril. 2002;78(1):34–9.CrossRefPubMed
11.
Garcia-Velasco JA, Moreno L, Pacheco A, Guillén A, Duque L, Requena A, Pellicer A. The aromatase inhibitor letrozole increases the concentration of intraovarian androgens and improves in vitro fertilization outcome in low responder patients: a pilot study. Fertil Steril. 2005;84(1):82–7.CrossRefPubMed
12.
Vendola KA, Zhou J, Adesanya OO, Weil SJ, Bondy CA. Androgens stimulate early stages of follicular growth in the primate ovary. J Clin Invest. 1998;101(12):2622–9.PubMedCentralCrossRefPubMed
13.
Mitwally MF, Casper RF. Use of an aromatase inhibitor for induction of ovulation in patients with an inadequate response to clomiphene citrate. Fertil Steril. 2001;75(2):305–9.CrossRefPubMed
14.
Al-Inany HG, Abou-Setta AM, Aboulghar M. Gonadotrophin-releasing hormone antagonists for assisted conception. Cochrane Database Syst Rev. 2006;(3):CD001750.
15.
Al-Inany HG, Youssef MA, Aboulghar M, Broekmans F, Sterrenburg M, Smit J, Abou-Setta AM. Gonadotrophin – releasing hormone antagonists for assisted reproductive technology. Cochrane Database Syst Rev. 2011;(5): CD001750.
16.
van der Gaast MH, Eijkemans MJ, van der Net JB, de Boer EJ, Burger CW, van Leeuwen FE, Fauser BC, Macklon NS. Optimum number of oocytes for a successful first IVF treatment cycle. Reprod Biomed Online. 2006;13(4):476–80.CrossRefPubMed
17.
Revelli A, Casano S, Salvagno F, Piane LD. Milder is better? Advantages and disadvantages of “mild” ovarian stimulation for human in vitro fertilization. Reprod Biol Endocrinol. 2011;9:25.PubMedCentralCrossRefPubMed
18.
Hohmann FP, Macklon NS, Fauser BC. A randomized comparison of two ovarian stimulation protocols with gonadotropine-releasing hormone (GnRH) antagonist co-treatment for in vitro fertilization commencing recombinant follicle-stimulating hormone on cycle day 2 or 5 with the standard long GnRH agonist protocol. J Clin Endocrinol Metab. 2003;88(1):166–73.CrossRefPubMed
19.
Baart EB, Martini E, Eijkemans MJ, Van Ostal D, Beckers NG, Verhoeff A, Macklon NS, Fauser BC. Milder ovarian stimulation for in vitro fertilization reduces aneuploidy in the human preimplantation embryo: a randomised controlled trial. Hum Reprod. 2007;22(4):980–8.CrossRefPubMed
20.
Hejinen EM, Eijkemans MJ, De Klerk C, Polinder S, Beckers NG, Klinkert ER, et al. A mild treatment strategy for in vitro fertilization: a randomised non inferiority trial. Lancet. 2007;369(9563):743–9.CrossRef
21.
Verberg MF, Macklon NS, Nargund G, Frydman R, Devroey P, Broekmans FJ, Fauser BC. Mild ovarian stimulation for IVF. Hum Reprod Update. 2009;15(1):13–29.CrossRefPubMed
22.
Lekamge DN, Lane M, Gilchrist RB, Tremellen KP. Increased gonadotrophin stimulation does not improve IVF outcomes in patients with predicted poor ovarian reserve. J Assist Reprod Genet. 2008;25(11):515–21.PubMedCentralCrossRefPubMed
23.
Land JA, Yarmolinskaya MI, Dumoulin JC, Evers JL. High-dose human menopausal gonadotropin stimulation in poor responders does not improve in vitro fertilization outcome. Fertil Steril. 1996;65(5):961–5.PubMed
24.
Check JH. Mild ovarian stimulation. J Assist Reprod Genet. 2007;24(12):621–7.PubMedCentralCrossRefPubMed
25.
Dhont M, Onghena A, Coetsier T, De Sutter P. Prospective randomized study of clomiphene citrate and gonadotrophins versus goserelin and gonadotrophins for follicular stimulation in assisted reproduction. Hum Reprod. 1995;10(4):791–6.PubMed
26.
Lin YH, Hwang JL, Seow KM, Huang LW, Hsieh BC, Tzeng CR. Comparison of outcome of clomiphene citrate/human menopausal gonadotropine/cetrorelix protocol and buserelin long protocol- a randomized study. Gynecol Endocrinol. 2006;22(6):297–302.CrossRefPubMed
27.
Grabia A, Papier S, Pesce R, Mlayes L, Kopelman S, Sueldo C. Preliminary experience with a low-cost stimulation protocol that includes letrozole and human menopausal gonadotropins in normal responders for assisted reproductive technologies. Fertil Steril. 2006;86(4):1026–8.CrossRefPubMed
28.
Verpoest WM, Kolibianakis E, Papanikolaou E, Smitz J, Van Steirteghem A, Devroey P. Aromatase inhibitors in ovarian stimulation for IVF/ICSI: a pilot study. Reprod Biomed Online. 2006;13(2):166–72.CrossRefPubMed
29.
Valbuena D, Jasper M, Remohi J, Pellicer A, Simon C. Ovarian stimulation and endometrial receptivity. Hum Reprod. 1999;14 Suppl 2:107–11.CrossRefPubMed
30.
Katz-Jaffe MG, Trounson AO, Cram DS. Chromosome 21 mosaic human preimplantation embryos predominantly arise from diploid conceptions. Fertil Steril. 2005;84(3):634–43.CrossRefPubMed
31.
Munne S, Magli C, Adler A, Wright G, de Boer K, Mortimer D, Tucker M, Cohen J, Gianaroli L. Treatment-related chromosome abnormalities in human embryos. Hum Reprod. 1997;12(4):780–4.CrossRefPubMed
32.
Simon C, Cano F, Valbuena D, Remohi J, Pellicer A. Clinical evidence for a detrimental effect on uterine receptivity of high serum oestradiol concentrations in high and normal responder patients. Hum Reprod. 1995;10(9):2432–7.CrossRefPubMed
33.
Horcajadas JA, Mínguez P, Dopazo J, Esteban FJ, Domínguez F, Giudice LC, Pellicer A, Simón C. Controlled ovarian stimulation induces a functional genomic delay of the endometrium with potential clinical implications. J Clin Endocrinol Metab. 2008;93(11):4500–10.CrossRefPubMed
34.
Haouzi D, Assou S, Dechanet C, Anahory T, Dechaud H, De Vos J, Hamamah S. Controlled ovarian hyperstimulation for in vitro fertilization alters endometrial receptivity in humans: protocol effects. Biol Reprod. 2010;82(4):679–86.CrossRefPubMed
35.
Devroey P, Bourgain C, Macklon NS, Fauser BC. Reproductive biology and IVF: ovarian stimulation and endometrial receptivity. Trends Endocrinol Metab. 2004;15(2):84–90.CrossRefPubMed
36.
Martínez-Conejero JA, Simón C, Pellicer A, Horcajadas JA. Is ovarian stimulation detrimental to the endometrium? Reprod Biomed Online. 2007;15(1):45–50.CrossRefPubMed
37.
Olivius C, Friden B, Borg G, Bergh C. Why do couples discontinue in vitro fertilization treatment? A cohort study. Fertil Steril. 2004;81(2):258–61.CrossRefPubMed
38.
Verberg HF, Eijkemans MJ, Macklon NS, Heijnen EM, Fauser BC, Broekmans FJ. Predictors of ongoing pregnancy after single-embryo transfer following mild ovarian stimulation for IVF. Fertil Steril. 2008;89(5):1159–65.CrossRefPubMed
39.
de Klerk C, Heijnen EM, Macklon NS, Duivenvoorden HJ, Fauser BC, Passchier J, Hunfeld JA. The psychological impact of mild ovarian stimulation combined with single embryo transfer compared with conventional IVF. Hum Reprod. 2006;21(3):721–7.CrossRefPubMed
40.
de Klerk C, Macklon NS, Hejinen EMEW, Eijkemans MJC, Fauser BCJM, Passchier J, Hunfeld JAM. The psychological impact of IVF failure after two or more cycles of IVF with a mild versus standard treatment strategy. Hum Reprod. 2007;22(9):2554–8.CrossRefPubMed
41.
Devroey P, Aboulghar M, Garcia-Velasco J, Griesinger G, Humaidan P, Kolibianakis E, Ledger W, Tomás C, Fauser BC. Improving the patient’s experience of IVF/ICSI: a proposal for an ovarian stimulation protocol with GnRH antagonist co-treatment. Hum Reprod. 2009;24(4):764–77.CrossRefPubMed
42.
Polinder S, Heijnen EMEW, Macklon NS, Habbema JDF, Fauser BJCM, Eijemans MJC. Cost-effectiveness of a mild compared with a standard strategy for IVF: a randomized comparison using cumulative term live birth as the primary endpoint. Hum Reprod. 2008;23(2):316–23.CrossRefPubMed
43.
Aboulghar MA, Mansour RT, Serour GA, Amin YM, Sattar MA, Ramzy AM. In vitro fertilization in a spontaneous cycle: a successful simple protocol. J Obstet Gynaecol. 1995;21:337–40.CrossRef
44.
Nargund G, Waterstone J, Bland J, Philips Z, Parsons J, Campbell S. Cumulative conception and live birth rates in natural (unstimulated) IVF cycles. Hum Reprod. 2001;16(2):259–62.CrossRefPubMed
45.
Kolibianakis E, Zikopoulos K, Camus M, Tournaye H, Van Steirteghem A, Devroey P. Modified natural cycle for IVF does not offer a realistic chance of parenthood in poor responders with high day 3 FSH levels, as a last resort prior to oocyte donation. Hum Reprod. 2004;19(11):2545–9.CrossRefPubMed
46.
Hur C, Lee W, Lim J. Outcome of minimal stimulation IVF with short-term application of GnRH antagonist and low dose gonadotropins in natural cycle and cycles using clomiphene citrate in poor responders. Fertil Steril. 2005;84 Suppl 1:S325.CrossRef
47.
Elizur SE, Aslan D, Shulman A, Weisz B, Bider D, Dor J. Modified natural cycle using GnRH antagonist can be an optional treatment in poor responders undergoing IVF. J Assist Reprod Genet. 2005;22(2):75–9.PubMedCentralCrossRefPubMed
48.
Pelinck MJ, Vogel NE, Hoek A, Simons AH, Arts EG, Mochtar MH, Beemsterboer S, Hondelink MN, Heineman MJ. Cumulative pregnancy rates after three cycles of minimal stimulation IVF and results according to subfertility diagnosis: a multicentre cohort study. Hum Reprod. 2006;21(9):2375–83.CrossRefPubMed