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Towards better quality research in recurrent implantation failure: standardizing its definition is the first step
RBMOnline - Vol 12. No 3. 2006 383-385 Reproductive BioMedicine Online; www.rbmonline.com/Article/2167 on web 24 January 2006
Short communication Towards better quality research in recurrent implantation failure: standardizing its definition is the first step Tarek El-Toukhy1, Mohamed Taranissi Assisted Reproduction and Gynaecology Centre (ARGC), 13 Upper Wimpole Street, London WIM 7TD, UK. 1 Correspondence: Tel: +44 207 486 1230; Fax: +44 207 486 1232; e-mail: [email protected]
Abstract Recurrent implantation failure is a frustrating condition for clinicians and patients alike. The number of potential therapies offered to patients in order to overcome this problem is increasing, and more research is needed to establish which of those treatment options is truly beneficial. Improved understanding of their value is more likely if the same definition of recurrent implantation failure is used across future studies. In this article, the inconsistency present in current literature is examined and the case is argued for a standardized definition for the condition. Keywords: IVF failure, IVF standardization, recurrent implantation failure, research in IVF Despite its gradual improvement over the last two decades, the success rate of IVF has remained relatively low. This means that the majority of couples seeking IVF may have to undergo more than one cycle of treatment to achieve a pregnancy and that, unfortunately, many will remain childless even after multiple attempts. Implantation failure is a major clinical dilemma, since its potential causes are often complex and poorly understood. Desperate to achieve a successful outcome, and tired of repeating the same treatment protocols, couples who experience recurrent IVF implantation failure (RIF) are turning to new treatment technologies before clear evidence to prove their safety and benefit is established. Various treatment modalities applied at different stages of the treatment cycle have been suggested for the management of RIF such as preimplantation genetic screening (PGS) using either fluorescent in-situ hybridization or comparative genomic hybridization, assisted hatching, blastocyst culture, immune testing and therapy, cytoplasmic transfer, embryo co-culture, sequential embryo transfers, zygote tubal transfer, and using fibrin glue at embryo transfer. The use of most of those proposed treatments is based on logical postulations and presumptions and, at best, limited data, but lacks substantive proof of clinical efficacy from randomized studies. Nevertheless, there is already evidence that their use is escalating internationally. For example, European Society of Human Reproduction and Embryology (ESHRE) preimplantation genetic diagnosis (PGD) consortium data published in 2005 (Sermon et al., 2005) showed that the most common indication for PGS is RIF, despite the lack of prospective randomized studies in favour of PGS. A recent review (Urman et al., 2005) addressed the lack of sufficient data to prove the value of those treatment modalities,
and called for them to be tested in well-designed controlled trials in order to clarify their place in the management of patients with RIF. The difficulty and expense of performing large randomized trials, however, means that there will be increasing reliance on pooling of data from multiple smaller studies for the majority of the new treatments. Therefore, it is utterly incomprehensible how controlled studies can be uniformly designed when presently there is lack of a standardized definition for RIF. Before such trials can be conducted, clinicians must agree and standardize the definition of RIF first, as this will help the process of collection and analysis of data from different studies in order to shape scientific consensus. In this respect, we need to examine the components of the term ‘recurrent implantation failure’.
‘Recurrent’ Currently, there are two traditional definitions for RIF. The first definition refers to patients who have had at least three failed IVF attempts. However, many published studies investigating new therapies for RIF have included patients after two failed cycles only (Kwak-Kim et al., 2003; Munné et al., 2003; Demirol and Gurgan, 2004; Kahraman et al., 2004; Wilding et al., 2004; Check et al., 2005). Even the same group of researchers have alternated between using two or three failed cycles as the definition of RIF to suit different studies (Ng et al., 2002; Kwak-Kim et al., 2003). The adherence to a specified number of failed cycles is vital since the likelihood of a successful outcome varies depending on the cycle order. Studies that looked at pregnancy and live birth rates after successive IVF attempts showed that the chance of pregnancy per cycle tends to remain stable in the
383
Short communication - Standardization in recurrent implantation failure - T El-Toukhy & M Taranissi first three attempts, but declines afterwards (Croucher et al., 1998; Templeton and Morris, 1998; Osmanagaoglu et al., 1999; Nargund et al., 2001; Sharma et al., 2002). Thus, including patients after only two failed cycles may overestimate the benefit of the treatment modality in question (Egger and Smith, 1995). The second definition of RIF is failure of IVF after cumulative transfer of more than 10 embryos of high quality (Stern et al., 1998; Voullaire et al., 2002; Inagaki et al., 2003; Thornhill et al., 2005). This arbitrary definition is more subjective, since it relies on each clinic’s criteria of what represents a good quality embryo. Furthermore, if the definition is applied in many European countries to women younger than 40 years, those patients will have had five or more failed IVF attempts before they are considered under the umbrella of RIF. The discrepancy between the two definitions could potentially introduce significant heterogeneity when comparing results from different studies, thus limiting their usefulness. On the other hand, the total number of embryos replaced per RIF patient could be a useful variable when comparing between the different groups in controlled studies, particularly in view of the presence of numerous embryo transfer policies among individual IVF clinics. Finally, the nature of the transfer cycle – whether using fresh or cryothawed embryos – can impact on the likelihood of implantation. Improvement in ovarian stimulation and embryo cryopreservation protocols, coupled with the growing tendency to replace fewer embryos, will inevitably increase the chance of couples achieving embryo freezing. Cryothawed embryo replacements have on average a 30% lower chance of pregnancy compared with fresh embryo transfers (Edgar et al., 2000; Wright et al., 2005). Thus, it is necessary to clarify whether the three failed cycles were all fresh transfers or had included one or more cryothawed embryo transfers. Clearly, the prognosis for a second fresh cycle in a patient who had three failed transfers (one fresh and two subsequent cryothawed attempts) is likely to be better than that in a patient who had three consecutive failed fresh cycles. It is, therefore, prudent to adhere to only one definition and standardize the minimum number of failed fresh cycles couples have to undergo before they are included in future controlled trials investigating new therapies for RIF.
Implantation failure
384
Clinicians have yet to agree the definition of implantation failure, and in many studies no definition is described in the methodology section. Some investigators consider it to indicate a negative pregnancy test 2 weeks after embryo transfer (i.e. IVF failure). Others use the term to indicate either absence of a gestational sac on ultrasound 5 weeks after transfer or of a fetal heartbeat at or beyond 3 weeks of pregnancy, and some even consider failure as absence of a live birth after IVF (Munné et al., 2003; Takahashi et al., 2004; Check et al., 2005; Thornhill et al., 2005). The latter group of investigators, thus, include patients who had a biochemical pregnancy or clinical miscarriage within the limits of implantation failure. There is considerable evidence to suggest that patients who had conceived after previous IVF treatment could expect a better
chance of pregnancy in subsequent cycles, compared with those who had a negative pregnancy test after IVF (Tan et al., 1994; Molloy et al., 1995; Croucher et al., 1998; Templeton and Morris, 1998; Bates and Ginsburg, 2002; El-Toukhy et al., 2003). Therefore, the lack of a clear demarcation between conception failure, implantation failure and pregnancy failure can introduce a degree of bias into RIF studies (Easterbrook et al., 1991). Arguably, patients who repeatedly show no evidence of a gestational sac or fetal heartbeat on scanning despite an initial rise of their β-human chorionic gonadotrophin (HCG) levels might be better studied separately from those who repeatedly fail to conceive after embryo transfer. At least, the proportion of RIF patients who had previously achieved an IVF pregnancy (miscarriage or live birth) should be explicitly reported in future studies.
Influence of the treating centre Another issue that is often overseen when recruiting RIF patients into research trials is the impact of the overall success rate of the treating centre on cycle outcome. IVF results vary considerably between individual clinics. In the UK, for example, the live birth rate per embryo transfer among IVF clinics in 2002 ranged between 9% and 59% in women younger than 35 years, and between 0% and 21% in women aged 40–42 years (Human Fertilisation and Embryology Authority, 2005). Clinics which have facilities to provide treatment for RIF patients are usually large clinics with wide experience, and are likely to be among those with the better results (Gianaroli et al., 2005; Verlinsky et al., 2005). Clearly, an improvement in outcome after treatment would be expected, regardless of whether the new technology in question is used or not. For the same reason, uncontrolled studies of new treatment modalities in RIF patients are prone to bias since they can show a high pregnancy rate that is actually related to the background expertise of the treating centre rather than the treatment modality tested. Although this factor is difficult to standardize, future studies should include, as a minimum requirement, data on what percentage of their RIF patients had treatment failure at the authors’ institution before the index cycle. In conclusion, high-quality research in the rapidly expanding area of management of RIF is urgently required. The lack of an agreed and a standardized definition for RIF is an international problem that could limit the value and reliability of such research. Fertility specialists should strive to provide as accurate information as possible in order for their RIF patients to make an informed choice regarding new technologies introduced into practice. For this information to be available, researchers must adhere to one agreed definition of RIF in future studies. We hope the arguments raised in this article will help us to do so.
References Bates GW Jr, Ginsburg ES 2002 Early pregnancy loss in in-vitro fertilization is a positive predictor of subsequent IVF success. Fertility and Sterility 77, 337–341. Check JH, Liss JR, Check ML et al. 2005 Lymphocyte immunotherapy can improve pregnancy outcome following embryo transfer (ET) in patients failing to conceive after two previous ET. Clinical and Experimental Obstetrics and Gynecology 32, 21–22. Croucher C, Lass A, Maragara R, Winston R 1998 Predictive value of
Short communication - Standardization in recurrent implantation failure - T El-Toukhy & M Taranissi the results of a first in-vitro fertilization cycle on the outcome of subsequent cycles. Human Reproduction 13, 403–408. Demirol A, Gurgan T 2004 Effect of treatment of intrauterine pathologies with office hysteroscopy in patients with recurrent IVF failures. Reproductive BioMedicine Online 8, 590–594. Easterbrook PJ, Berlin JA, Gopalan R, Matthews DR 1991 Publication bias in clinical research. Lancet 337, 867–872. Edgar D, Bourne H, Speirs A, McBain J 2000 A quantitative analysis of the impact of cryopreservation on the implantation potential of human early cleavage stage embryos. Human Reproduction 15, 175–179. Egger M, Smith GD 1995 Misleading meta-analysis. British Medical Journal 310, 752–754. El-Toukhy T, Khalaf Y, Al-Darazi K et al. 2003 Cryo-thawed embryos obtained from conception cycles have double the implantation and pregnancy potential of those from unsuccessful cycles. Human Reproduction 18, 1313–1318. Gianaroli L, Magli MC, Ferrarelli AP et al. 2005 The beneficial effects of preimplantation genetic diagnosis for aneuploidy support extensive clinical application. Reproductive BioMedicine Online 10, 633–640. Human Fertilisation and Embryology Authority 2005 The HFEA Guide to Infertility and Directory of Clinics 2005/06. HFEA, London. Kahraman S, Benkhalifa M, Donmez E et al. 2004 The results of aneuploidy screening in 276 couples undergoing assisted reproductive techniques. Prenatal Diagnosis 24, 307–311. Kwak-Kim JY, Chung-Bang HS, Ng SC et al. 2003 Increased T helper 1 cytokine responses by circulating T cells are present in women with recurrent pregnancy losses and infertile women with multiple implantation failures after IVF. Human Reproduction 18, 767–773. Inagaki N, Stern C, McBain J et al.2003 Analysis of intra-uterine cytokine concentration and matrix-metalloproteinase activity in women with recurrent failed embryo transfer. Human Reproduction 18, 608–615. Molloy D, Doody ML, Breen T 1995 Second time around: a study of patients seeking second assisted reproduction pregnancies. Fertility and Sterility 64, 546–551. Munné S, Sandalinas M, Escudero T et al. 2003 Improved implantation after preimplantation genetic diagnosis of aneuploidy. Reproductive BioMedicine Online 7, 91–97. Nargund, G, Waterstone J, Bland JM et al. 2001 Cumulative conception and live birth rates in natural (unstimulated) IVF cycles. Human Reproduction 16, 259–262. Ng SC, Gilman-Sachs A, Thaker P et al. 2002 Expression of intracellular Th1 and Th2 cytokines in women with recurrent spontaneous abortion, implantation failures after IVF/ET or normal pregnancy. American Journal of Reproductive Immunology 48, 77–86. Osmanagaoglu K, Tournaye H, Camus M et al. 1999 Cumulative delivery rates after intracytoplasmic sperm injection: 5 year follow-up of 498 patients. Human Reproduction 14, 2651–2655. Sermon K, Moutou C, Harper JC et al. 2005 ESHRE PGD Consortium data collection IV: May–December 2001. Human Reproduction 20, 19–34. Sharma V, Allgar V, Rajkhowa M 2002 Factors influencing the cumulative conception rate and discontinuation of in vitro fertilization treatment for infertility. Fertility and Sterility 78, 40–46. Stern C, Chamley D, Hale L et al. 1998 Antibodies to beta2 glycoprotien I are associated with in vitro fertilization implantation failure as well recurrent miscarriage: results of a prevalence study. Fertility and Sterility 70, 938–944. Takahashi K, Mukaida T, Tomiyama T et al. 2004 GnRh antagonists improved blastocyst quality and pregnancy outcome after multiple failures of IVF/ICSI-ET with a GnRH agonist protocol. Journal of Assisted Reproduction and Genetics 21, 317–322. Tan SL, Doyle P, Maconochie N et al. 1994 Pregnancy and birth rates of live infants after in vitro fertilization in women with and without previous in vitro fertilization pregnancies: a study of eight thousand cycles at one center. Amerian Journal of Obstetrics and
Gynecology 170, 34–40. Templeton A, Morris J 1998 Reducing the risk of multiple births by transfer of two embryos after in vitro fertilization. New England Journal of Medicine 339, 573–577. Thornhill AR, deDie-Smulders CE, Geraedts JP et al. 2005 ESHRE PGD Consortium ‘Best practice guidelines for clinical preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)’. Human Reproduction 20, 35–48. Urman B, Yakin K, Balaban B 2005 Recurrent implantation failure in assisted reproduction: how to counsel and manage. B. Treatment options that have not been proven to benefit the couple. Reproductive BioMedicine Online 11, 382–391. Verlinsky Y, Tur-Kaspa I, Cieslak J et al. 2005 Preimplantation testing for chromosomal disorders improves reproductive outcome in poor prognosis patients. Reproductive BioMedicine Online 11, 219–225. Wilding M, Forman R, Hogewinf G et al. 2004 Preimplantation genetic diagnosis for the treatment of failed in vitro fertilizationembryo transfer and habitual abortion. Fertility and Sterility 81, 1302–1307. Wright VC, Schieve LA, Reynolds MA, Jeng, G 2005 Assisted Reproductive Technology Surveillance – United States, 2002. MMWR Surveillance Summaries 54, 1–24. Voullaire L, Wilton L, McBain J et al. 2002 Chromosome abnormalities identified by comparative genomic hybridization in embryos from women with repeated implantation failure. Molecular Human Reproduction 8, 1035–1041. Received 28 November 2005; refereed 12 December 2005; accepted 9 January 2006.
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Short communication Towards better quality research in recurrent implantation failure: standardizing its definition is the first step Tarek El-Toukhy1, Mohamed Taranissi Assisted Reproduction and Gynaecology Centre (ARGC), 13 Upper Wimpole Street, London WIM 7TD, UK. 1 Correspondence: Tel: +44 207 486 1230; Fax: +44 207 486 1232; e-mail: [email protected]
Abstract Recurrent implantation failure is a frustrating condition for clinicians and patients alike. The number of potential therapies offered to patients in order to overcome this problem is increasing, and more research is needed to establish which of those treatment options is truly beneficial. Improved understanding of their value is more likely if the same definition of recurrent implantation failure is used across future studies. In this article, the inconsistency present in current literature is examined and the case is argued for a standardized definition for the condition. Keywords: IVF failure, IVF standardization, recurrent implantation failure, research in IVF Despite its gradual improvement over the last two decades, the success rate of IVF has remained relatively low. This means that the majority of couples seeking IVF may have to undergo more than one cycle of treatment to achieve a pregnancy and that, unfortunately, many will remain childless even after multiple attempts. Implantation failure is a major clinical dilemma, since its potential causes are often complex and poorly understood. Desperate to achieve a successful outcome, and tired of repeating the same treatment protocols, couples who experience recurrent IVF implantation failure (RIF) are turning to new treatment technologies before clear evidence to prove their safety and benefit is established. Various treatment modalities applied at different stages of the treatment cycle have been suggested for the management of RIF such as preimplantation genetic screening (PGS) using either fluorescent in-situ hybridization or comparative genomic hybridization, assisted hatching, blastocyst culture, immune testing and therapy, cytoplasmic transfer, embryo co-culture, sequential embryo transfers, zygote tubal transfer, and using fibrin glue at embryo transfer. The use of most of those proposed treatments is based on logical postulations and presumptions and, at best, limited data, but lacks substantive proof of clinical efficacy from randomized studies. Nevertheless, there is already evidence that their use is escalating internationally. For example, European Society of Human Reproduction and Embryology (ESHRE) preimplantation genetic diagnosis (PGD) consortium data published in 2005 (Sermon et al., 2005) showed that the most common indication for PGS is RIF, despite the lack of prospective randomized studies in favour of PGS. A recent review (Urman et al., 2005) addressed the lack of sufficient data to prove the value of those treatment modalities,
and called for them to be tested in well-designed controlled trials in order to clarify their place in the management of patients with RIF. The difficulty and expense of performing large randomized trials, however, means that there will be increasing reliance on pooling of data from multiple smaller studies for the majority of the new treatments. Therefore, it is utterly incomprehensible how controlled studies can be uniformly designed when presently there is lack of a standardized definition for RIF. Before such trials can be conducted, clinicians must agree and standardize the definition of RIF first, as this will help the process of collection and analysis of data from different studies in order to shape scientific consensus. In this respect, we need to examine the components of the term ‘recurrent implantation failure’.
‘Recurrent’ Currently, there are two traditional definitions for RIF. The first definition refers to patients who have had at least three failed IVF attempts. However, many published studies investigating new therapies for RIF have included patients after two failed cycles only (Kwak-Kim et al., 2003; Munné et al., 2003; Demirol and Gurgan, 2004; Kahraman et al., 2004; Wilding et al., 2004; Check et al., 2005). Even the same group of researchers have alternated between using two or three failed cycles as the definition of RIF to suit different studies (Ng et al., 2002; Kwak-Kim et al., 2003). The adherence to a specified number of failed cycles is vital since the likelihood of a successful outcome varies depending on the cycle order. Studies that looked at pregnancy and live birth rates after successive IVF attempts showed that the chance of pregnancy per cycle tends to remain stable in the
383
Short communication - Standardization in recurrent implantation failure - T El-Toukhy & M Taranissi first three attempts, but declines afterwards (Croucher et al., 1998; Templeton and Morris, 1998; Osmanagaoglu et al., 1999; Nargund et al., 2001; Sharma et al., 2002). Thus, including patients after only two failed cycles may overestimate the benefit of the treatment modality in question (Egger and Smith, 1995). The second definition of RIF is failure of IVF after cumulative transfer of more than 10 embryos of high quality (Stern et al., 1998; Voullaire et al., 2002; Inagaki et al., 2003; Thornhill et al., 2005). This arbitrary definition is more subjective, since it relies on each clinic’s criteria of what represents a good quality embryo. Furthermore, if the definition is applied in many European countries to women younger than 40 years, those patients will have had five or more failed IVF attempts before they are considered under the umbrella of RIF. The discrepancy between the two definitions could potentially introduce significant heterogeneity when comparing results from different studies, thus limiting their usefulness. On the other hand, the total number of embryos replaced per RIF patient could be a useful variable when comparing between the different groups in controlled studies, particularly in view of the presence of numerous embryo transfer policies among individual IVF clinics. Finally, the nature of the transfer cycle – whether using fresh or cryothawed embryos – can impact on the likelihood of implantation. Improvement in ovarian stimulation and embryo cryopreservation protocols, coupled with the growing tendency to replace fewer embryos, will inevitably increase the chance of couples achieving embryo freezing. Cryothawed embryo replacements have on average a 30% lower chance of pregnancy compared with fresh embryo transfers (Edgar et al., 2000; Wright et al., 2005). Thus, it is necessary to clarify whether the three failed cycles were all fresh transfers or had included one or more cryothawed embryo transfers. Clearly, the prognosis for a second fresh cycle in a patient who had three failed transfers (one fresh and two subsequent cryothawed attempts) is likely to be better than that in a patient who had three consecutive failed fresh cycles. It is, therefore, prudent to adhere to only one definition and standardize the minimum number of failed fresh cycles couples have to undergo before they are included in future controlled trials investigating new therapies for RIF.
Implantation failure
384
Clinicians have yet to agree the definition of implantation failure, and in many studies no definition is described in the methodology section. Some investigators consider it to indicate a negative pregnancy test 2 weeks after embryo transfer (i.e. IVF failure). Others use the term to indicate either absence of a gestational sac on ultrasound 5 weeks after transfer or of a fetal heartbeat at or beyond 3 weeks of pregnancy, and some even consider failure as absence of a live birth after IVF (Munné et al., 2003; Takahashi et al., 2004; Check et al., 2005; Thornhill et al., 2005). The latter group of investigators, thus, include patients who had a biochemical pregnancy or clinical miscarriage within the limits of implantation failure. There is considerable evidence to suggest that patients who had conceived after previous IVF treatment could expect a better
chance of pregnancy in subsequent cycles, compared with those who had a negative pregnancy test after IVF (Tan et al., 1994; Molloy et al., 1995; Croucher et al., 1998; Templeton and Morris, 1998; Bates and Ginsburg, 2002; El-Toukhy et al., 2003). Therefore, the lack of a clear demarcation between conception failure, implantation failure and pregnancy failure can introduce a degree of bias into RIF studies (Easterbrook et al., 1991). Arguably, patients who repeatedly show no evidence of a gestational sac or fetal heartbeat on scanning despite an initial rise of their β-human chorionic gonadotrophin (HCG) levels might be better studied separately from those who repeatedly fail to conceive after embryo transfer. At least, the proportion of RIF patients who had previously achieved an IVF pregnancy (miscarriage or live birth) should be explicitly reported in future studies.
Influence of the treating centre Another issue that is often overseen when recruiting RIF patients into research trials is the impact of the overall success rate of the treating centre on cycle outcome. IVF results vary considerably between individual clinics. In the UK, for example, the live birth rate per embryo transfer among IVF clinics in 2002 ranged between 9% and 59% in women younger than 35 years, and between 0% and 21% in women aged 40–42 years (Human Fertilisation and Embryology Authority, 2005). Clinics which have facilities to provide treatment for RIF patients are usually large clinics with wide experience, and are likely to be among those with the better results (Gianaroli et al., 2005; Verlinsky et al., 2005). Clearly, an improvement in outcome after treatment would be expected, regardless of whether the new technology in question is used or not. For the same reason, uncontrolled studies of new treatment modalities in RIF patients are prone to bias since they can show a high pregnancy rate that is actually related to the background expertise of the treating centre rather than the treatment modality tested. Although this factor is difficult to standardize, future studies should include, as a minimum requirement, data on what percentage of their RIF patients had treatment failure at the authors’ institution before the index cycle. In conclusion, high-quality research in the rapidly expanding area of management of RIF is urgently required. The lack of an agreed and a standardized definition for RIF is an international problem that could limit the value and reliability of such research. Fertility specialists should strive to provide as accurate information as possible in order for their RIF patients to make an informed choice regarding new technologies introduced into practice. For this information to be available, researchers must adhere to one agreed definition of RIF in future studies. We hope the arguments raised in this article will help us to do so.
References Bates GW Jr, Ginsburg ES 2002 Early pregnancy loss in in-vitro fertilization is a positive predictor of subsequent IVF success. Fertility and Sterility 77, 337–341. Check JH, Liss JR, Check ML et al. 2005 Lymphocyte immunotherapy can improve pregnancy outcome following embryo transfer (ET) in patients failing to conceive after two previous ET. Clinical and Experimental Obstetrics and Gynecology 32, 21–22. Croucher C, Lass A, Maragara R, Winston R 1998 Predictive value of
Short communication - Standardization in recurrent implantation failure - T El-Toukhy & M Taranissi the results of a first in-vitro fertilization cycle on the outcome of subsequent cycles. Human Reproduction 13, 403–408. Demirol A, Gurgan T 2004 Effect of treatment of intrauterine pathologies with office hysteroscopy in patients with recurrent IVF failures. Reproductive BioMedicine Online 8, 590–594. Easterbrook PJ, Berlin JA, Gopalan R, Matthews DR 1991 Publication bias in clinical research. Lancet 337, 867–872. Edgar D, Bourne H, Speirs A, McBain J 2000 A quantitative analysis of the impact of cryopreservation on the implantation potential of human early cleavage stage embryos. Human Reproduction 15, 175–179. Egger M, Smith GD 1995 Misleading meta-analysis. British Medical Journal 310, 752–754. El-Toukhy T, Khalaf Y, Al-Darazi K et al. 2003 Cryo-thawed embryos obtained from conception cycles have double the implantation and pregnancy potential of those from unsuccessful cycles. Human Reproduction 18, 1313–1318. Gianaroli L, Magli MC, Ferrarelli AP et al. 2005 The beneficial effects of preimplantation genetic diagnosis for aneuploidy support extensive clinical application. Reproductive BioMedicine Online 10, 633–640. Human Fertilisation and Embryology Authority 2005 The HFEA Guide to Infertility and Directory of Clinics 2005/06. HFEA, London. Kahraman S, Benkhalifa M, Donmez E et al. 2004 The results of aneuploidy screening in 276 couples undergoing assisted reproductive techniques. Prenatal Diagnosis 24, 307–311. Kwak-Kim JY, Chung-Bang HS, Ng SC et al. 2003 Increased T helper 1 cytokine responses by circulating T cells are present in women with recurrent pregnancy losses and infertile women with multiple implantation failures after IVF. Human Reproduction 18, 767–773. Inagaki N, Stern C, McBain J et al.2003 Analysis of intra-uterine cytokine concentration and matrix-metalloproteinase activity in women with recurrent failed embryo transfer. Human Reproduction 18, 608–615. Molloy D, Doody ML, Breen T 1995 Second time around: a study of patients seeking second assisted reproduction pregnancies. Fertility and Sterility 64, 546–551. Munné S, Sandalinas M, Escudero T et al. 2003 Improved implantation after preimplantation genetic diagnosis of aneuploidy. Reproductive BioMedicine Online 7, 91–97. Nargund, G, Waterstone J, Bland JM et al. 2001 Cumulative conception and live birth rates in natural (unstimulated) IVF cycles. Human Reproduction 16, 259–262. Ng SC, Gilman-Sachs A, Thaker P et al. 2002 Expression of intracellular Th1 and Th2 cytokines in women with recurrent spontaneous abortion, implantation failures after IVF/ET or normal pregnancy. American Journal of Reproductive Immunology 48, 77–86. Osmanagaoglu K, Tournaye H, Camus M et al. 1999 Cumulative delivery rates after intracytoplasmic sperm injection: 5 year follow-up of 498 patients. Human Reproduction 14, 2651–2655. Sermon K, Moutou C, Harper JC et al. 2005 ESHRE PGD Consortium data collection IV: May–December 2001. Human Reproduction 20, 19–34. Sharma V, Allgar V, Rajkhowa M 2002 Factors influencing the cumulative conception rate and discontinuation of in vitro fertilization treatment for infertility. Fertility and Sterility 78, 40–46. Stern C, Chamley D, Hale L et al. 1998 Antibodies to beta2 glycoprotien I are associated with in vitro fertilization implantation failure as well recurrent miscarriage: results of a prevalence study. Fertility and Sterility 70, 938–944. Takahashi K, Mukaida T, Tomiyama T et al. 2004 GnRh antagonists improved blastocyst quality and pregnancy outcome after multiple failures of IVF/ICSI-ET with a GnRH agonist protocol. Journal of Assisted Reproduction and Genetics 21, 317–322. Tan SL, Doyle P, Maconochie N et al. 1994 Pregnancy and birth rates of live infants after in vitro fertilization in women with and without previous in vitro fertilization pregnancies: a study of eight thousand cycles at one center. Amerian Journal of Obstetrics and
Gynecology 170, 34–40. Templeton A, Morris J 1998 Reducing the risk of multiple births by transfer of two embryos after in vitro fertilization. New England Journal of Medicine 339, 573–577. Thornhill AR, deDie-Smulders CE, Geraedts JP et al. 2005 ESHRE PGD Consortium ‘Best practice guidelines for clinical preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)’. Human Reproduction 20, 35–48. Urman B, Yakin K, Balaban B 2005 Recurrent implantation failure in assisted reproduction: how to counsel and manage. B. Treatment options that have not been proven to benefit the couple. Reproductive BioMedicine Online 11, 382–391. Verlinsky Y, Tur-Kaspa I, Cieslak J et al. 2005 Preimplantation testing for chromosomal disorders improves reproductive outcome in poor prognosis patients. Reproductive BioMedicine Online 11, 219–225. Wilding M, Forman R, Hogewinf G et al. 2004 Preimplantation genetic diagnosis for the treatment of failed in vitro fertilizationembryo transfer and habitual abortion. Fertility and Sterility 81, 1302–1307. Wright VC, Schieve LA, Reynolds MA, Jeng, G 2005 Assisted Reproductive Technology Surveillance – United States, 2002. MMWR Surveillance Summaries 54, 1–24. Voullaire L, Wilton L, McBain J et al. 2002 Chromosome abnormalities identified by comparative genomic hybridization in embryos from women with repeated implantation failure. Molecular Human Reproduction 8, 1035–1041. Received 28 November 2005; refereed 12 December 2005; accepted 9 January 2006.
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