HUMAN FERTILISATION & EMBRYOLOGY AUTHORITY THE SCIENTIFIC AND CLINICAL ADVANCES GROUP

Transcription

1 HUMAN FERTILISATION & EMBRYOLOGY AUTHORITY THE SCIENTIFIC AND CLINICAL ADVANCES GROUP EMBRYO TRANSFER REVIEW 1. Members are asked to consider the embryo transfer review paper SCAG (04/03)01. Issues to consider 2. Members are asked to consider the literature review and to consider the following issues: To consider the issue raised in this current brief review, in particular: The methodology to be used in monitoring the new two embryo policy, this includes the proposal that embryo transfers and pregnancy outcomes can be recorded through the Registry on the treatment forms. A report could possibly be made available to Members of SCAG towards the end of the year on the data collected. The evidence available for more than two embryos to be transferred in poor prognosis patients The impact that the new HFEA policy will have on clinics. The evidence for moving towards an elective one embryo transfer policy. Future work for SCAG. Christina Panton HFEA Executive April

2 HUMAN FERTILISATION & EMBRYOLOGY AUTHORITY THE SCIENTIFIC AND CLINICAL ADVANCES GROUP EMBRYO TRANSFER REVIEW 1. Background 1.1 Several European states now routinely limit embryo replacement to two embryos per cycle and others are also pushing for the reduction to single embryo transfers (Van Royen et al 1999). By contrast in the USA the replacement of five or even six embryos is allowed under certain circumstances (SART Guidelines, November 1999). Against this background of seriously conflicting views the HFEA decided in 2001 to re-examine its embryo replacement policy to see whether it remains appropriate. 1.2 The original embryo transfer policy amended in August 2001 stated: As a consequence of the review, the Authority has decided to revise its policy on embryo transfer, reducing the number of embryos to normally be transferred from three to two. In exceptional circumstances, a three egg or three embryo transfer may be performed. These exceptional circumstances will be case specific, (HFEA CH (08)01). 1.3 Technology in the field of ART has improved considerably in the 12 years since the HFE Act 1990 was passed. Live birth rates in IVF have increased from 14% per treatment cycle in 1991/2 to a national average of 21.8% in 2000/ However, more recent analysis of data submitted to the HFEA for the year April 2000/2001 indicates 109 sets of triplets (1.7%) and 1579 sets of twins (25%) born from cycles undertaken. The range of two embryo transfer cycles varied substantially between an excess of 80% elective transfer of 2 embryos (18 out of 64 centres) to less than 20% (4 clinics) regardless of age. One third of the centres (21/64) accounted for 53% of the live-born triplets and more than 50% of their transfers were 3 embryos (Braude 2003 unpublished). These figures reflect the unacceptably high rate of multiple pregnancy and the inconsistency in which centres have applied the exceptional circumstances provision. 1.5 The HFEA has recently announced, through it s launch of the 6 th edition of the Code of Practice, a revised policy for the number of embryos that should be transferred in any given treatment cycle as follows: To reduce the risk of multiple pregnancy, centres are expected to place no more than either two eggs or two embryos in a woman in any one cycle 2

3 1.6 This new policy has now been enshrined in the 6 th edition in paragraph The statement removes the notion that three embryos can be transferred in exceptional circumstances. However, a number of factors still remain that require careful consideration. As the following discussion supports, many patients will benefit from the two embryos transfer policy with little affect on their success rates, but their will be a small number of patients that may benefit from a higher number of embryos to be transferred. In addition, there is demonstrable inconsistency in the application of the 2 embryo transfer policy implemented in August 2001, as demonstrated by the Audit report attached in (Appendix A) where it is shown that in one particular centre over 90% of embryo transfers were three embryo transfers. 2. Professional Guidelines 2.1 This change in practice is reflected in the guidelines of both the British Fertility Society and the Royal College of Obstetrics and Gynaecology. 2.2 The BFS recommendations for good practice state that all possible efforts should be made to avoid multiple pregnancies. It then states that it should be usual practice to transfer a maximum of two embryos in each treatment cycle. 2.3 The RCOG s Evidence-Based Clinical Guidance No.6 states that a reduction in the number of multiple pregnancies resulting from assisted reproduction is of national importance and that every attempt should be made to avoid multiple births and particularly triplets, following IVF treatment. There follows a recommendation that a maximum of two embryos should be transferred in women under 40 years of age. 2.4 The Eshre Capri Workshop recommended either two or three embryos to be transferred depending on female age. However, in a more recent recommendation it was suggested that the number of embryos to be transferred should be limited to two (Eshre Workshop Group 2000) 3. International Laws and Policies relating to embryo transfer 3.1 The following international laws and policies have been noted: 3.2 Reproductive Technology (Code of Ethical Clinical Practice) Regulations of Southern Australia States that transferring more than three embryos or eggs in any one cycle is not permitted. 3.3 Select Committee on The Human Reproductive Technology Act 1991 Report (Western Australia) States that up to three embryos can be transferred in any one cycle., although an from Sandra Webb from the Western Australia Reproductive Technology Council indicates that the Act itself does not set a limit. Instead, practitioners must maintain the standards set by the Reproductive Technology Accreditation Committee. These encourage two, but may allow three or even four in exceptional circumstances. 3

4 3.4 Infertility Treatment Authority, Victoria, Australia, Conditions of Licence Allows more than four embryos to be transferred in exceptional circumstances, especially if the woman is over Guidelines of the German Medical Association Two embryo transfer recommended. 3.6 ESHRE Guidelines for Good Practice in IVF Laboratories Makes a general recommendation against transferring more than two embryos. 3.7 Netherlands Health Council s Report on IVF (1997) Normally no more than two and never more than three embryos are to be transferred at any one time. 3.8 Fertility Society of Australia Code of Practice for Centres using Assisted Reproductive Technology States that for women over 40, the low implantation rate makes it permissible to transfer even more than four embryos or oocytes. 4. Multiple Births 4.1 There is continuing concern about the high incidence of multiple births following IVF treatment. Many authors have confirmed that multiple births are an avoidable complication resulting in high perinatal morbidity and mortality (Petterson et al., 1993; FIVNAT 1995; Dunn and McFarlane., 1996) and significant financial (Callahan et al 1994; Mugford and Henderson 1995) and Psychological (Garel et al.,1997) consequences. 4.2 Infants born after IVF in Australia were more likely to require neonatal ventilator use than non-ivf infants, irrespective of whether they were born as a singleton or multiple pregnancies (Leslie et al 1992). They were more likely to utilise the resources of neonatal intensive care units, but less likely to visit GPs or other health workers during their first year of life (Leslie et al., 1998). The increased need for neonatal care has been attributed to the well known increased rate of preterm births and multiple births and multiple birth after IVF (Gissler et al 1995; Bergh et al 1999). 4.3 More recently, much attention has been given to the economic impact of multiple gestations (Elster 2000; Jones 2003 PhD thesis, unpublished data). 4.4 A study by Ericson et al., 2002 confirms and extends previously published observations that the main increased utilization of health care by IVF children occurs during the first period of life. This study shows that IVF children have an increased use of in patient care, not only in the neonatal period but for some years afterwards. The article concludes that by reducing the rate of twin births by using one embryo transfer a substantial saving in hospital cost could be achieved, which could then balance the extra number of embryo transfers needed in order to obtain a pregnancy. 4

5 5. Reduction of Multiple Births 5.1 The best way of reducing the number of multiple births is to reduce the number of embryos placed in a woman in the course of IVF treatment. It is also possible to reduce the incidence of multiple births by fetal reduction after implantation has occurred however the procedure is invasive and it is important to remember that embryo reduction may be accompanied by, long term psychological side effects. Embryo reduction should be regarded as a useful tool but not as a means to facilitate high order embryo transfers (Wennerholm et al., 2000). 5.2 The number of fetal reductions recorded in the National Statistics Series AB no 28, Abortion Statistics 2001 HMSO 2002(Appendix B) shows that for 2001 : 49 cases in all to women resident in Eng & Wales (of which 22 were carried out under Section 1(1)(d)[ that there is a substantial risk that if the child were born it would suffer from such physical or mental abnormalities as to be seriously handicapped] and the further 28 under [Section 1(1)(a) that the pregnancy has not exceeded its twenty-fourth week and that the continuance of the pregnancy would involve risk, greater than if the pregnancy were terminated, of injury to the physical or mental health of the pregnant woman or any existing children of her family] and [Section 1(1)(b) that the termination is necessary to prevent grave permanent injury to the physical or mental health of the pregnant woman]. 5.3 It is not recorded which of these pregnancies resulted from assisted conception. 5.4 Details of procedures are collected on the abortion notification form HSA4. This form must be submitted to the CMO within 14 days of the procedure. It is a criminal offence not to notify such a procedure under the Abortion Act 1967 as amended by section 37 of the HFEA Act There is no evidence to suggest significant under-reporting from centres (Appendix. 6. Two Embryo Transfer 6.1 In order to further reduce the multiple pregnancy rates especially triplet pregnancies, replacement of only 2 embryos has been advocated by many authors (Waterstone et al., 1991; Templeton and Morris 1998; Nijs et al 1993; Staessen et al. 1993; Vauthier 1994; Fujii 1998; Devreker1999; Dean 2000; Ernest Hung Yu Ng et al 2001). 6.2 Further to the studies mentioned above, Engmann et al 2001 conducted one of the first studies in a single centre in the UK that spanned a period both before and after the HFEA s policy of limiting the number of embryos transferred to three. 5

6 6.3 They argue that previous studies investigating factors associated with the probability of multiple birth, and examining how limiting the number of embryos transferred affects the probability of both birth and multiple births, have tended to be based on either relatively small data series (Nijs et al., 1993; Staesen et al., 1993; Bassl et al 1997; Elsner et al 1997) or on pooling of heterogenous data from several different clinics (Templeton and Morris, 1998; Schieve et al 1999). 6.4 This study examined trends over time, in the probability of birth (single or multiple) and the proportion of multiple births among deliveries, using data from a single centre in the UK between 1984 and 1997 which spanned periods pre and post HFEA legislation. Their study suggests that increasing the number of embryos transferred has little or no effect on the probability of birth, but merely increases the probability of multiple birth. The authors encourage a reduction in the number of embryos to be transferred. 6.5 Given that in a majority of the cases an embryo never reaches the uterine cavity in vivo at 48 72h, which is the case in the majority of IVF cycles today, recent studies by (Hernandez 2001;Hamberger & Hazekamp 2002) discuss the importance of optimisation of culture conditions. Optimising the culture conditions would permit a better selection of embryos and perhaps a more optimal timing for replacement. A number of specific problems related to IVF embryo transfer policy can be identified that require optimisation. These include; natural or stimulated cycle; fertilisation; culture of embryos; PGD; freezing of oocytes and embryos; embryo reduction; patient age. 7. Patient Age 7.1 Poor reproductive outcomes in older patients undergoing IVF embryo transfer with their own oocytes have been well documented (Van Blerkom et al., 1995; Grasie et al., 1997; Janny and Menezeo, 1996). However, high pregnancy rates have been reported in women of advanced reproductive age following the transfer of embryos obtained from oocytes from younger women (Navot et al 1994). This suggests that endometrial receptivity in some older patients may not be compromised and that their poor performance is largely due to poor quality oocytes and embryos. A study by Obasaju M et al 2001 confirms, as with other authors, that aneuploidy is the principal cause of the poor pregnancy prognosis observed in women of this age group. This study demonstrates that acceptable pregnancy rates can be obtained from the transfer of single chromosomally normal embryos in women over 40 years of age despite the high rate of aneuploidy detected. 7.2 A paper by Licciardi et al 2001 examined whether limiting the number of embryos transferred in an oocyte donation program can maintain acceptable pregnancy rates while reducing the overall risk of multiple birth. The model demonstrated that in good prognosis patients, the implantation and pregnancy rates were not compromised by limiting the number of embryos replaced. The article also argued that where the ASRM has recommended that the presence of frozen embryos be considered when determining the embryo transfer number in patients under 35 years, the authors were of the view that they did not observe a difference in pregnancy rate relative to 6

7 cryopreservation status and suggested that the decision to transfer fewer embryos be independent of that. 7.3 In light of the above discussion it is interesting to note that in the data provided by the HFEA to the EIM 2000 (Appendix C) that 931 three embryo transfers were carried out compared to 912 two embryo transfers for oocyte recipients in the higher age group of patients. 8. The move towards a single embryo transfer 8.1 In contradiction to Licciardi et al 2001 above, clinical data provided by Tiitinen et al., 2001 showed that elective single embryo transfer with a good cryopreservation programme results in very acceptable pregnancy rates with a low risk for twins in a selected patient group. 8.2 A more recent study (Sutter et al., 2002) has shown that more ART cycles are required to obtain the same number of children born following single embryo transfer compared to two embryo transfer. Single embryo transfer allows the avoidance of twins and thus diminishes pregnancy-related and neonatal care costs. The authors showed that two embryo transfer is more effective in terms of child per cycle rate, but single embryo transfer is as cost effective per child born. Twins originating from two embryo transfer increase the indirect and long tem costs of neonatal care; however these were not discussed in this paper.the real advantage of single embryo transfer is the avoidance of the very high long term costs resulting from the increased morbidity of twins after birth. 8.3 The decrease in the number of embryos transferred from two to one is feasible in at least one third of the population of patients, reducing the twin incidence to approximately half of its original incidence and maintaining a high overall pregnancy rate. The most suitable group of patients are young women in their first IVF/ICSI cycle (Martikainen et al., 2001; Gerris et al., 2002) Combining validated strict growth criteria of early cleaving embryos with a clinical profile of the twin prone patient as described by some authors (Strandell et al 2000) would be a most successful combination. 8.4 A Recommendation made by Eshre Campus Course Report 2001 states: A twin or higher order MP of 25% or more is not acceptable and must induce practitioners to elaborate an individualised embryo transfer strategy aiming to reduce this incidence to perhaps 10%. 8.5 Elective single embryo transfer should be recommended if at least 2 conditions are met. Patient is twin prone needs defining If a top quality embryo can be transferred what is the definition of a top quality embryo and how could this be made consistent amongst centres. 7

8 9. Discussion 9.1 Given the heterogeneity within IVF couples, many centres may consider the current limit of two embryos to be quite restrictive and impeding on clinical judgement. Many practitioners consider that individualisation of the number transferred according to different personal criteria is the best way to improve the chances of success for a given couple. Factors that should be considered are usually; age of woman, number of attempts, embryo quality and fertilisation rate. 9.2 Perhaps the biggest challenge persisting in the field of human ART is to identify the most developmentally competent embryos available so that fewer embryos of higher quality are transferred. Only then will the goal of maximising the pregnancy rate while minimising the risk of a high order multiple gestation be achieved. 9.3 Cohen et al., 2001 discusses the many explanations for the fact that no consensus can be reached on the strategies to avoid multiple pregnancies in ART; Teams in IVF are not always the same as the obstetrical ones and usually not the same teams as those that follow through the patients complications. The fact that triplets are not always an obstetrical problem even though it is always a psychological, economical and social complication. The fact that a twin pregnancy even though it is often less complicated than a triplet one, induces 42% of prematurity (55% are before 32 weeks) and more than 3% of twins die in utero or are neonatal deaths. This is not well known. The fact that women and couples are unaware of the difficulties of multiple pregnancies and births bring pressure on the doctors to replace a maximum number of embryos to increase their chances. The fact that IVF teams take in to account the financial factors of the couple and try to give them as maximum chance as they can on each attempt. The fact that not all teams have at their disposal a good cryopreservation program. 9.4 A strategy of elective transfer of two embryos would probably be largely acceptable if: A good selection of high quality embryos on day 3 would allow a high rate of transfer of one or two blastocysts. Good results of cryopreservation program were part of the agreement of an IVF centre. The singleton live birth rates were the principal outcome of ART reported by centres and registries, twins and triplets should be reported separately. Financial considerations could improve. Public or private insurers and patients could be informed that the limited costs of reimbursement of IVF/ICSI procedures will be regained by the prevention of large costs of children born from multiple pregnancies. 9.5 Finally, there is evidence to suggest a possible move towards an elective one embryo transfer. It is clear from the evidence available that this would be successful in certain 8

9 patient groups. The implementation of such a policy requires extensive counselling of the infertile couple, appropriate legislation and a strict selection criteria (Pinborg et., 2003). 10. Conclusion 10.1 This review would indicates that the current HFEA two embryo transfer policy is appropriate practice for good prognosis patients and in some cases selected patient groups would benefit from elective one embryo transfer. Such a policy would significantly reduce the multiple pregnancy rates in clinics without reducing the overall live birth rates It is important that the HFEA maintains a continuing monitoring process to ensure that this new policy is implemented correctly. The HFEA should use its extensive data base to monitor the implementation of the two embryo transfer policy and to provide an evidence base to support centres and the Authority when reviewing the live birth rates. This will ensure that centres maintain a consistent approach to this policy and maintain best practice. 11. Issues to consider: 11.1 Members are asked to consider the literature review and to consider the following issues: To consider the issue raised this current brief review, in particular: The methodology to be used in monitoring the new two embryo policy, this includes the proposal that embryo transfers and pregnancy outcomes can be recorded through the Registry on the treatment forms. A report could possibly be made available to Members of SCAG towards the end of the year on the data collected. The evidence available for more than two embryos to be transferred in poor prognosis patients The impact that the new HFEA policy will have on clinics. The evidence for moving towards an elective one embryo transfer policy. Future work for SCAG. Christina Panton HFEA Executive April

10 APPENDIX A Progress Report on the Audit (Data Register Project) (Presented as part of the above report to The Authority Meeting Held in February 2003) Transfers of 3 or more embryos We looked at 610 embryo transfers, of which 85 (14%) were 3-embryo transfers. In some cases (notably centres 068, 069, 032) reasons were not recorded for the 3- embryo transfer. We noted particularly high rates of 3-embryo transfer from the samples examined at the following centres: Centre Embryo transfers examined 3-embryo transfers % 3-embryo transfers % % % % 10

11 Licensed Fertility Treatment: Selective Terminations Lord Alton of Liverpool asked Her Majesty's Government: APPENDIX B How many pregnancies arising out of licensed fertility treatment have been selectively terminated in each of the past five years; at what stage of gestation was each pregnancy terminated; and on what ground of the Abortion Act 1967 (as amended) was each abortion performed.[hl2146] Baroness Andrews: Information on whether selective terminations of pregnancy were performed following licensed fertility treatment is not collected centrally as it is not a requirement of the Abortion Regulations Information is collected on gestation and grounds and is shown in the following table. Data are for all selective terminations performed in England and Wales in the past five years. 1 Apr 2003 : Column WA121 Number of selectively terminated pregnancies, by gestation and grounds under the Abortion Act 1967, as amended, in England and Wales, 1997 to 2001 Year Gestation in weeks Section 1(1)(a) Section 1(1)(b) Section 1(1)(c) Section 1(1)(d) 1997 under to to and over Total under to to and over Total under to to and over Total under to to and over Total under Total 11

12 9 to to and over Total Prepared by Department of Health, Statistics Division 3G. 1. Data for 2002 will be available later this year. 2. The grounds under the Act are as follows: Section 1(1)(a) that the pregnancy has not exceeded its twenty-fourth week and that the continuance of the pregnancy would involve risk, greater than if the pregnancy were terminated, of injury to the physical or mental health of the pregnant woman or any existing children of her family; or Section 1(1)(b) that the termination is necessary to prevent grave permanent injury to the physical or mental health of the pregnant woman; or Section 1(1)(c) that the continuance of the pregnancy would involve risk to the life of the pregnant woman, greater than if the pregnancy were terminated; or Section 1(1)(d) that there is a substantial risk that if the child were born it would suffer from such physical or mental abnormalities as to be seriously handicapped. 12

13 APPENDIX C European IVF Monitoring (EIM) 2000 Name of country United Kingdom (Please note that these figures have yet to be audited or verified by the HFEA) Name and full address of contact person. Richard Baranowski Human Fertilisation & Embryology Authority Paxton House 30 Artillery Lane London E1 7LS Telephone +44 (0) Fax +44 (0) richard.baranowski@hfea.gov.uk Please return prior to 1 st of april 2003 to ESHRE Central Office Van Aakenstraat 41 B-1850 Grimbergen, Belgium Tlf FAX bruno.vandeneede@eshre.com 13

14 European IVF monitoring (EIM) 2000 Module 0 Number and size of clinics IVF clinics (units) in the country Number Total number of clinics in the country 75 Total number of clinics reporting to the National Register 75 Size of the clinics. (Based on the total annual number of IVF, ICSI, FER and ED combined) Number of clinics < 100 cycles cycles cycles cycles 24 > cycles 7 14

15 15 SCAG(04/03)01

16 European IVF monitoring (EIM) 2000 Module 1 a IVF and ICSI fresh cycles Number of treatments and pregnancies IVF (n) ICSI (n) All (n) Initiated cycles Aspirations Transfers, all Transfer 1 embryo * ( all ) Transfer 2 embryos Transfer 3 embryos Transfer 4 or more embryos Pregnancies**, all * Indicate if possible the number of elective single embryo transfers after IVF and ICSI combined : Not possible * Indicate - if possible the number of elective dual embryos transfer after IVF and ICSI combined : Not possible ** Please use the WHO definition of clinical pregnancy: evidence of pregnancy by clinical or ultrasound parameters (ultrasound visualisation of a gestational sac). It includes ectopic pregnancy. Multiple gestational sacs in one patient are counted as one clinical pregnancy. 16

17 Currently, the HFEA makes use of only 1 index for clinical pregnancy - detection of fetal pulsation on ultrasound and so cannot supply the number of clinical pregnancies exactly as defined by WHO. 17

18 European IVF monitoring (EIM) 2000 Module 1 a Number of treatments and pregnancies FER. Frozen embryo (or 2 PN) replacements IVF (n) ICSI (n) All (n) Thawings Transfers, all Transfer of 1 embryo Transfers of 2 embryos Transfers of 3 embryos Transfers of 4 or more embryos Pregnancies, all Egg donations Donation cycles Transfers, all Transfer 1 embryo IVF (n) ICSI (n) All (n) Transfer 2 embryos Transfer 3 embryos

19 Transfer of 4 or more embryos Pregnancies, all

20 European IVF monitoring (EIM) 2000 Module 1 a. Preimplantation Genetic Diagnosis (PGD) Number of treatments, pregnancies and deliveries ( n ) Initiated cycles Aspirations Transfers Pregnancies Deliveries Not available Not available Not available Not available Not available 20

21 European IVF monitoring (EIM) Module 1b Female age Number of initiated cycles in specific age groups in relation to treatment. IVF ICSI EGG DONATION Age < Age Age Age Age > All women

22 European IVF monitoring (EIM) 2000 Module 1 c Complications to treatments and fetal reduction Complications with admission to hospital Number Hyperstimulation syndrome 376 Complications to oocyte retrieval (all) 120 Bleeding 6 Infection 0 Maternal death (documented) Not available Fetal reduction 82 22

23 European IVF monitoring 2000 Module 2ART deliveries resulting from treatments performed in 2000 IVF (n) ICSI (n) FER (n) Egg Donation (n) PGD (n) Clinical pregnancies (all) Not available Documented pregnancy losses (abortions and ectopic pregnancies) Not available Lost for follow-up Not available Singleton deliveries Not available Twin deliveries Not available Triplet deliveries Not available Quadruplet deliveries Not available All deliveries Not available 23

24 BIBLIOGRAPHY Paper considered: Bassil S. Predictive factors for multiple pregnancy in in-vitro fertilisation. J. Reproduct. Med 42, Bergh et al., Deliveries and children born after in-vitro fertilisation in Sweden ; a retrospective cohort study. Lancet 354, Braude P., The UK legislative experience: A model for other countries. (2003 Unpublished paper). Callahan T. L., et al., The economic impact of multiple gestation pregnancies and the contributin of assisted reproduction. N. Engl. J Med., 331, Cohen et al. How to avoid Multiple Pregnancies in Asssited Reproductive Technologies. Seminars in reproductive Medicine Vol 19 N0. No Dean NL et al., Impact of reducing the number of embryos transferred form three to two in women under the age of 35 who produced three or more high-qulaity embryos. Ferility & Sterility 74: Devreker F et al., Comparison of two elective transfer policies of two embryos to reduce multiple pregnancies without impairing pregnancy rates. Human Reproduction 1999; 14: Elsner C.W., Multiple pregnancy rate and embryo transfer number during in vitro fertilisation Am J Obstet. Gynecol. 177, Elster N. Less is more: the risks of multiple births. The Institute for Science, law, and Technology Working Group on Reproductive Technology. Fertility and Sterility Oct; 74(4): Ericson et al., Hospitalisation of infants born after IVF. Human Reproduction Vol 17, No. 4 pp , Ernest Hung Yu Ng et al 2001: Transfer of two embryos instead of three will not compromise pregnancy rate but will reduce multiple pregnancy rate in an assisted reproduction unit. J. Obstet. Gynaecol. Res Vol 23 No E. Van Royen, K. Mangelschots et al., Characterization of a top quality embryo, a step towards single-embryo transfer, Human Reproduction, vol.14 no.9, pp , 1999 Engmann et al. Trends in the incidence of births and multiple birthe and the factors that determine the probability of multiple birth after IVF treatment. Human Reproduction Vol 16 No. 12 pp , SART Guidelines, November A. Dunn & A. Macfarlane, Recent trends in the incidence of multiple births and associated mortality in England and Wales, Archives of Disease in Childhood 75, F10-F19, Ericson et al: Hosptal care utilization of infants born after IVF. Human Reproduction Vol 17. No.4 pp ,

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27 Wennerholm U.B., et al., Incidence of congenital malformations in children born after ICSI. Human Reproduction 15,