Cumulative live birth rates in cohorts of patients treated with in vitro fertilization or intracytoplasmic sperm injection

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1 Cumulative live birth rates in cohorts of patients treated with in vitro fertilization or intracytoplasmic sperm injection Cynthia Witsenburg, M.D., Sandra Dieben, M.D., Lucette Van der Westerlaken, M.Sc., Harjo Verburg, M.D., and Nico Naaktgeboren, Ph.D. IVF Center, Leiden University Medical Center, Leiden, The Netherlands Objective: Follow-up of IVF/intracytoplasmic sperm injection (ICSI) patients to obtain accurate information concerning chances of live birth as well as early treatment dropout. Comparison of the cumulative pregnancy rates, established in cohorts, with those estimated with life table analysis to determine which method provides the most accurate data without overestimation. Design: Retrospective longitudinal cohort study. Setting: Academic medical IVF center. Patient(s): All 750 patients from the Leiden IVF center and another 706 patients from cooperating clinics starting IVF/ICSI treatment in the period Intervention(s): All observations were part of standard IVF/ICSI and cryopreservation protocols. Main Outcome Measure(s): Endpoints of this study were a first live birth or termination of treatment. Treatment cycles were followed until the end of 2002, pregnancy follow-up through September Result(s): The cumulative live birth rate for the Leiden cohort was 59.1%. In yearly cohorts this varied from 54.8% to 67.1%. Cumulative live birth rates were 61.8% 63.2% for unexplained infertility (n 229), endometriosis (n 19), and andrologic indication (n 223). For tubal (n 129) and hormonal (n 46) indications the rates were 55.8% and 45.7%, respectively. The group of egg donation or surrogacy (n 10) reached 40.0%, and patients with two or more indications (n 84) 56.0%. For women 35 years of age the cumulative live birth rate was 64.6%, for women years of age it was 48.7%, and for women years of age 31.0%. Conclusion(s): In contrast to estimation of expected cumulative pregnancy rates the cohort measurement does not overestimate success rates. It accurately reflects chances of both live birth as well as early treatment dropout. The cumulative live birth rate was 59.1%. Over time results improved and the contribution of cryopreservation increased. (Fertil Steril 2005;84: by American Society for Reproductive Medicine.) Key Words: Cumulative live birth rate, IVF/ICSI cohorts, cryopreservation, BESST Couples at the onset of IVF/intracytoplasmic sperm injection (ICSI) treatment are facing a pathway that is intense, uncertain, and not without risks. To avoid needless treatment with unnecessary disappointment and costs it is important to make accurate estimates of the chance of achieving a live birth as well as the chance of dropping out of the treatment program before that time. Knowledge about the multiple birth rate is also important. Since the introduction of IVF in 1978 (1) approximately 1,000,000 children have been born by means of IVF and ICSI treatments. Over the years results have become better, although the numbers of multiples remained too high. Most reports and registries consider pregnancy or birth rates per treatment cycle or embryo transfer (ET) (2 5). It is therefore not possible to determine whether the birth rate per patient increased to the same extent. For couples about to Received June 22, 2004; revised and accepted February 22, Reprint requests: Nico Naaktgeboren, Ph.D., IVF Center, Leiden University Medical Center H3-P-26, P.O. Box 9600, 2300 RC Leiden, The Netherlands (FAX: ; n.naaktgeboren@lumc.nl). start an IVF/ICSI treatment it is more important to know the ultimate chance of having a baby rather than the success rate per cycle. In this respect it is also important for the couples concerned to be correctly informed about the chance of achieving a single or multiple pregnancy and birth. A major challenge for the centers is to obtain the highest possible birth rate while reducing multiple births to a minimum. Some studies report success as cumulative (live) birth or pregnancy rates after multiple IVF/ICSI treatments (6 9). A popular tool for estimating the cumulative success rates is the life table analysis (10). However, using this type of analysis to report the outcome of fertility treatments is highly questionable because it tends to overestimate success rates. Some other investigators show both the observed and the expected values, but prefer to report the estimated outcome (11 13). Overestimation of results is also present in studies that use modified models that estimate the so called pessimistic, realistic, and optimistic or crude and expected cumulative live birth rates (CLBR) (14, 15). The fact that some patients drop out also influences the final cumulative success rate (16). Another way of presenting fertility /05/$30.00 Fertility and Sterility Vol. 84, No. 1, July 2005 doi: /j.fertnstert Copyright 2005 American Society for Reproductive Medicine, Published by Elsevier Inc. 99

2 treatment outcome was published in a recent debate: BESST (birth emphasizing a successful singleton at term) was proposed as the most relevant standard of success (17). It is our belief that the cohort study design in which couples are followed over a longer period of time will provide realistic information. It accurately reflects the chance of a live birth after IVF/ICSI treatment without overestimating success rates. It can also provide accurate data about both the singleton and multiple birth rates and information about the chance of early dropout of the treatment program. In this study we followed two cohorts of patients. One cohort consisted of 750 couples that started their first IVF/ ICSI treatment between 1996 and 2000 at the Leiden University Medical Center. The second cohort was formed by 706 patients from transport IVF clinics, cooperating with our laboratory. Endpoints of the follow-up were a first live birth or discontinuation of treatment. Treatment results and pregnancies were recorded through December The live birth rates are updated to the end of September Cohorts were arranged by year of treatment onset, indication for treatment, and woman s age at the start of the treatment. MATERIALS AND METHODS Patients Between January 1996 and December 2000, 750 couples started their first IVF/ICSI treatment at the Leiden University Medical Center (LUMC) in the Netherlands. This cohort of patients was followed until the end of During the same period of time another cohort of 706 patients, treated in cooperation with three so-called transport clinics was studied. For the latter patient group, counseling, stimulation, monitoring, and oocyte pickups are provided by the transport clinics themselves. The actual laboratory procedures, ET, and cryopreservation are taken care of by our center. The 750 LUMC patients were studied in yearly cohorts. Cohorts per indication and women s age at the start of treatment were defined as well. The number of patients starting treatment each year varied from 128 to 164. The average women s age at treatment onset was 33.0 ( 4.0) years. As divided by age, 523 (69.7%) women were 36, 195 (26.0%) 36 39, and 32 (4.3%) 39 years at the start of the treatment. Indications for IVF/ICSI treatment were andrologic (n 233, 31.1%), tubal (n 129, 17.2%), hormonal (n 46, 6.1%), endometriosis (n 19, 2.5%), unexplained (n 229, 30.5%), egg donation or surrogacy (n 10, 1.3%), and multiple indications (n 84, 11.2%). The 706 patients of the transport clinics were studied as one cohort. The average age at treatment onset in this cohort was 33.2 ( 5.2) years. Because IVF, ICSI, and embryo cryopreservation are proven methods for the treatment of infertility there was no need for institutional review board approval. An informed consent is not necessary for a standard IVF procedure; however, written informed consent to perform ICSI and/or cryopreservation was obtained. IVF/ICSI Treatment The LUMC patients were stimulated according to a standard short stimulation protocol, starting by downregulation with an GnRH agonist on the first day of the menstruation as a nasal spray (Synarel, 1.2 mg daily; Pharmacia BV, Woerden, The Netherlands) or SC (Decapeptyl, 1.0 mg daily; Ferring, Hoofddorp, The Netherlands). This was followed by ovarian stimulation with purified urinary FSH (Metrodin; Serono, Geneva, Switzerland) or recombinant FSH (Gonal F; Serono) starting either on day 4 with 150 IU when the women were 37 years of age or younger, or on day 2 with 225 or 300 IU if the women were or years of age, respectively. The patients were monitored by vaginal ultrasound scans and serum E 2 measurement. If necessary the dose was adjusted during stimulation or in the following treatment cycle. When desired follicle growth was achieved, hcg (Profasi, 10,000 IU; Serono) was given SC, followed by oocyte pickup 36 hours later. After 1,598 oocyte retrievals, fertilization was performed by conventional IVF (n 1,125; 70.4%) or ICSI (n 473; 29.6%) following standard techniques. In general, the ET took place 3 days after the oocyte pickup, the maximum number of embryos per transfer being 2 for women younger than 38 years and 3 for women 38 years of age and above (average 2.00 embryos per transfer). As luteal support, progesterone (Progestan, 600 mg daily; Organon Oss, The Netherlands) was given vaginally starting the day after the pickup, and additional hcg (Pregnyl, 1,500 IU; Organon) was given SC 3 days after the transfer. The ovarian stimulation protocols in the transport clinics were similar; the percentage of cycles with ICSI was also similar to those in the LUMC cohort (32%). Embryo Cryopreservation The surplus of good quality embryos were cryopreserved on day 3 or 4 after oocyte pickup, using dimethyl sulfoxide (DMSO) as cryoprotectant. Transfers of cryopreserved embryos were performed preferably in spontaneous cycles. Pregnancy Definition A live birth is used as the main outcome in this study. A pregnancy was defined as an increasing -hcg 50 IU/L at 15 days and more after oocyte retrieval. Ongoing pregnancy was defined by the presence of a gestational sac with fetal heart activity after at least 12 weeks of gestation. Cohort Analysis All initiated treatment cycles were included in the cohort analysis. A treatment cycle was defined as the start of hormonal stimulation of the ovary, whether or not this would 100 Witsenburg et al. Cohort follow-up of IVF/ICSI patients Vol. 84, No. 1, July 2005

3 lead to ET. Patients remained in the cohort until the first live birth occurred. Continuation of treatment after a nonviable pregnancy, or a longer interval without treatment, was considered as part of the original cohort. Patients that did not resume treatment before the end of this study in December 2002 were considered as treatment dropouts. Success rates refer to the number of patients that started their first cycle within a specific cohort. Frozen ET cycles were not counted as separate treatment cycles. Pregnancies and live births that resulted from frozen embryos were referred to the cycle from which the embryos initially originated. Such a referral system becomes especially meaningful when determining the cumulative treatment effect per patient (18, 19). Statistical Analysis Differences in observed success rates between groups were analyzed by means of nonparametric statistics ( 2 ). P.05 was considered to be significant. All tests were performed using SPSS software (SPSS, Chicago, IL). RESULTS All the initiated cycles of the 750 patients of the LUMC cohort were included in this cohort study. The patients were followed until they had a first live birth after IVF/ICSI treatment in a freshly stimulated cycle or after cryopreservation, or until they stopped treatment unsuccessfully. In Table 1 the treatment results and the cumulative results are summarized. The average number of treatment cycles per patient was 2.4. For these patients a total of 1,826 cycles was started in the period of January 1996 to December This resulted in 1,598 oocyte pickups (92.8%) and 1,483 ETs (81.2% per started cycle). The average number of retrieved oocytes per pickup was 8.60, with a mean of 2.02 embryos per transfer. The pregnancy rate was 30.3% per freshly stimulated cycle and 32.0% with the results of cryopreservation included. For 139 patients 204 transfers of frozen/thawed embryos took place after the fresh cycle did not result in a pregnancy followed by a live birth. This procedure resulted in 32 pregnancies followed by the live birth of 16 singletons and 4 sets of twins. The live birth rate per patient was 14.4%. Transfers of cryopreserved embryos accounted for 5.5% of all achieved pregnancies and for 4.5% of all achieved live births. Over time the contribution of cryopreservation increased and the multiple pregnancy rate decreased (Table 1). Ultimately, 75.6% of the pregnancies resulted in a live birth, 74.3% of them singletons, 24.8% twins, and 0.9% (n 4) triplets. Two of the 4 triplet births originated from double ET. The multiple birth rate in the 1999 and 2000 cohorts (average 20%) was significantly ( 2 df 1; P.02) lower than in the cohorts started between 1996 and 1998 (average 30%). The live birth rate was 24.3% per started treatment cycle, including the births originating from cryopreservation. The pregnancy rate per ET was 37.3%, and the live birth rate was 29.9%. After oocyte retrieval, IVF was performed in 1,125 cases (70.4%) and ICSI in 473 (29.6%). Exactly the same percentages were found for the number of live births resulting from IVF (n 312) and ICSI (n 131). Because it TABLE 1 Summary of treatment results and cumulative live birth rates Total No. of patients No. of cycles ,826 No. of cycles per patient No. of pregnancies No. of pregnancies after cryo a No. of pregnancies, cryo a included No. of abortion/eug No. of live births, excluding cryo a No. of live births after cryo a Total no. of live births, cryo a included Contribution of cryo a to total births (%) Live birth rate per cycle (%) Multiple birth rate b Cumulative live birth rate per patient (%) a cryo cryopreservation and transfers after thawing. b Results of were significantly higher than in 1999 and 2000 (P.017). Fertility and Sterility 101

4 TABLE 2 Live birth per cycle and cumulative live birth rate per patient. Cycle number No. of patients started No. of patients stopped No. of patients with a live birth (after cryo) 199 (11) 136 (4) 64 (4) 23 (0) 11 (1) 7 (0) 3 (0) Live birth rate per patient started in cycle X (%) Live birth rate per patient started in cohort (%) Cumulative live birth rate per patient (%) Cumulative singleton birth rate per patient (%) Note: Five patients continued after the 7th cycle; no pregnancies were established in the following treatment cycles. appeared that the effectiveness of IVF and ICSI is equal, the cohorts were not separated for type of treatment. A first IVF/ICSI treatment cycle resulted in a live birth for 26.5% of the patients. For a second, third, and fourth cycle this value was 27.7%, 21.4%, and 15.2%, respectively. Ultimately, the CLBR was 59.1%, with a mean treatment period of 11 months and an average of 2.4 cycles per patient (Table 2, Fig. 1). Over time the results improved. The CLBR in the different yearly cohorts varied from 54.8% in 1996 to 67.1% in The CLBR was 43.9% for singletons, 14.7% for twins, and 0.5% for triplets. No selective fetal reduction was performed. More than 95% of these pregnancies and live births were achieved within 3 years after treatment onset. When the patients indication for IVF/ICSI treatment was taken into account, the CLBRs were as follows: endometriosis (n 19, CLBR 63.2%), unexplained infertility (n 229, CLBR 62.4%), andrologic indication (n 233, CLBR 61.8%), tubal infertility (n 129, CLBR 55.8%), and hormonal dysfunction (n 46, CLBR 45.7%). For the subgroup with unexplained infertility using donor semen (n 62) the CLBR reached 74.2%. In the cohort of patients with 2 or more different indications (n 84) a CLBR of 56.0% was found (Table 3). Only patients with infertility due to hormonal dysfunction had a significantly lower CLBR than the group with unexplained infertility (P.034). There was no significant difference in the average number of treatment cycles per patient between any of the mentioned indications. The CLBR for the different age groups decreases significantly with age: 64.6% for women younger than 36 years of age (n 523), 48.7% for women aged years (n 195), and 31.3% for women aged years (n 32) at the start of treatment ( 2 df 2; P.005) (Table 4). Only 39 of the 750 patients (5.2%) continued treatment up to a sixth cycle. In total, after 6 treatment cycles 440 patients (58.7%) achieved a live birth, 296 patients (39.5%) concluded treatment without achieving a live birth, and 14 patients (1.9%) continued treatment. Three of them became pregnant (Fig. 1). The cumulative success rates are influenced by the dropout rate during an IVF treatment (16). Figure 2 shows the association between the cumulative dropout rate after 2 cycles and the observed success rate determined in our cohort of patients and from published data (9, 11, 13 16, 20, 21). The higher the success, the lower the dropout rate. Figure 3 compares the cohort of our 750 LUMC patients with the cohort of the 706 patients from the transport IVF FIGURE 1 Cumulative live birth and dropout rate after IVF/ ICSI as function of treatment cycle number. The live births are subdivided into singletons in the black bands, twin births in blue bands, and triplet births in yellow bands. Patients continuing treatment are in gray bands and patients that stopped further treatment are in red bands. 102 Witsenburg et al. Cohort follow-up of IVF/ICSI patients Vol. 84, No. 1, July 2005

5 TABLE 3 Cumulative live birth rates per indication. Patients Treatment cycles Live births One single indication Tubal (55.8%) Andrological (61.8%) Unexplained (all) a (62.4%) Unexplained with donor semen (74.2%) Unexplained with own semen (58.1%) Hormonal a (45.7%) Endometriosis (63.2%) Egg donation or surrogacy (40.0%) Subtotal with single indication 666 1, (59.5%) Multifactorial indication (56.0%) Total 750 1, (59.1%) Note: Data are presented as number (percent of started patients). a P.05 for patients with hormonal subfertility compared with patients with unexplained infertility. clinics. Almost identical live birth rates per treatment cycle were found for the transport cohort as for our own cohort (24.4% vs. 24.3%). The CLBR per patient however was significantly (P.001) lower for the cohort of the transport IVF clinics: 49.4% vs. 59.1% (Fig. 3). Table 5 compares the actual observed success rates in cohorts with the calculated expected success rates after 3 and 5 or more treatment cycles, as reported in several recent studies (6 9, 11 16, 20, 21). To objectively interpret these data we used the ratio expected/observed success rates to express the extent of overrating. This ratio tended to get higher as the actual observed cumulative birth rates decreased. In addition, we observed that the ratio increased with longer follow-up periods (Fig. 4). DISCUSSION In this cohort study, the mean CLBR for couples starting their first IVF/ICSI treatment cycle between January 1996 and December 2000 (n 750) at the Leiden University Medical Center was 59.1%. Most of these pregnancies (399 90%) were achieved within the first 3 treatment cycles. Only 39 patients (5.2%) continued treatment up to a sixth cycle. More than 95% of all treatments took place within the first 3 years from treatment onset; therefore, a follow-up period with a minimum of 3 years is necessary to obtain reliable data about the final pregnancy and live birth chances. This study showed that by means of the follow-up of patient cohorts reliable information can be gathered on the cumulative outcome in IVF/ICSI programs. Such information is useful for the patient and also can be applied to compare results between centers or countries. The ultimate take-home baby rate depends on both the live birth rate per treatment cycle as well as the number of treatments per patient. The comparison between the cohort of patients starting in our clinic and the transport clinic cohort illustrates that with an almost equal live birth rate per treatment cycle of 24% the CLBR per patient can be significantly (P.001) different (59.1% and 49.4%, respectively). This discrepancy can be explained by the lower number of TABLE 4 Cumulative live birth rate per age group. 35 y y 40 y Total No. of patients No. of live births Cumulative live birth rate per patient (%) 64.6 a 48.7 a 31.3 a 59.1 a Results are significantly different (P.005). Fertility and Sterility 103

6 FIGURE 2 Relation of cumulative dropout rate after 2 treatment cycles and observed cumulative success rate. The letters B I correspond to the references as indicated in Table 5; A the data from this study. treatment cycles per patient in the transport clinic group (1.98 vs. 2.43). The lower number of cycles per patient in the transport clinic cohort is associated with a higher dropout rate, which causes a lower CLBR. This illustrates that the observed CLBR per patient after follow-up of cohorts contained more realistic information for the patient than the live birth rate per cycle. The question arises how long one should continue IVF/ ICSI treatment if pregnancy is not achieved. The cumulative dropout rate after the first 2 cycles was 15.5%. The almost doubling of the cumulative dropout rate from 15.5% to 26.7% after the third cycle not leading to pregnancy can most likely be explained by the reimbursement policy of the Dutch insurance companies. In most cases they paid only for a maximum of 3 treatment cycles. In our IVF center the maximum number of treatment cycles is usually set on 6. In the cohort 151 of the 351 women not pregnant after 3 cycles (43.0%) continued treatment. For these 151 women this resulted in 44 (29.1%) ongoing pregnancies, live birth rates per treatment cycle being approximately 15.5% for cycle number 4 to 7 (Table 2). The contribution to the overall CLBR may be rather small owing to the small number of patients (an increase from 53.2% to 59.1%), nevertheless continuation after 3 unsuccessful cycles for at least some patients may well be worthwhile, because almost one third of these couples obtained a first live birth after the third treatment cycle. Some women seem to be more fertile than others, even after IVF/ICSI treatment. Taking into account that after each treatment cycle a selection has taken place, the 2 then newly formed groups (pregnant and not pregnant) probably did not share the same characteristics at onset and therefore should not be compared. It is hypothesized that the patients who declined further treatment would have had the same chances as those that continued. After each unsuccessful treatment cycle the ultimate take-home baby chance will decrease and a higher proportion of patients will stop further treatment. Calculation with life table analysis of expected CLBRs overestimates the chances. Usually the reason for discontinuation of treatment is left out, but even when poor prognosis is taken into consideration (14, 15), this does not give all couples a realistic perspective concerning the ultimate treatment outcome. Owing to the considerable dropout rates and the assumption that patients who stop treatment would have had the same chances as those continuing treatment, the theoretically expected birth rate is always overestimated. We compared published data (Table 5, Figs. 2 and 4) and ascertained that the expected birth chances were overrated when established with life table analysis. The level of overrating increases with lower observed pregnancy rates, longer follow-up periods, and higher dropout rates (6 9, 11 16, 20, 21). The dropout rate, and consequently the observed/expected success ratio, seems to be affected by several patient characteristics. This can be illustrated in the studies by Osmanagaoglu et al.: In the testicular sperm extraction (TESE) group (21) as well as in the group FIGURE 3 Live birth rate per cycle (light blue bars) and cumulative live birth rate per patient (dark blue bars) for the LUMC cohort and the transport clinic cohort. a Results are significantly different (P.001). 104 Witsenburg et al. Cohort follow-up of IVF/ICSI patients Vol. 84, No. 1, July 2005

7 TABLE 5 Observed and expected cumulative live birth rates per started patient and ratio expected/observed cumulative live birth rate after 3 and after 5 or more cycles. Live birth rate after 3 cycles (%) Live birth rate after 5 or more cycles (%) Study a Observed Expected Ratio Observed Expected Ratio This study A Olivius et al. (15) B Stolwijk et al. (14) C De Jong et al. (9) D Land et al. (16) E Osmanagaoglu et al. (13) F Osmanagaoglu et al. b (21) G Osmanagaoglu et al. c (21) G Osmanagaoglu et al. (20) H De Mouzon et al. (11) I Dor et al. (6) Alsalili et al. (7) Engmann et al. (8) Fukuda et al. (12) d, 34 y Fukuda et al. (12) d, y Note: Ratio expected/observed cumulative live birth rate. a Studies with their reference number. The studies used in Figure 2 are indicated with the corresponding character. b G1 obstructive azoospermia group (21). c G2 nonobstructive azoospermia group (21). d Results for patients aged under 34 and years, respectively. 37 years of age (20) we see very high overrating ratios. For example, after a long follow-up in the TESE group with nonobstructive azoospermia, the calculated expected live birth rate reaches 65% but the actual observed birth rate is only 18% (Table 2). Patients may withdraw from treatment before a pregnancy has been achieved for various reasons. Financial, geographic, physical, as well as emotional aspects may all influence the decision. Therefore, a reliable estimation of expected birth rates cannot be made when a prognosis is based only on the ovary response to hormone stimulation, the number of oocytes retrieved at the pickup, or the number and quality of the transferred embryos in previous treatment cycles. Even the so-called realistic prognosis is overestimating the success rate (15). Calculation of the expected CLBRs cannot be based on pregnancy rates observed in the group that continue treatment only. Several patient characteristics, such as the indication for IVF/ICSI treatment, previous pregnancies, and woman s age at treatment onset, will influence the final chance of having a baby. It is therefore very important to consider the motivation to discontinue treatment in the patient group with premature treatment dropout. If not, the life table analysis will underestimate the chance of premature treatment dropout and will overrate the cumulative birth rate. As long as one cannot provide all these data, the only true realistic predictor remains the observed CLBR in patient cohorts. Owing to changes in laboratory techniques, ET policies, etc., results may differ over time. The cumulative outcome of yearly cohorts is an important tool to keep track of these changes in order to be able to provide couples accurate up-to-date information about their chances. For instance, the improvement of our ET technique (22) was reflected in the observed success rates for the cohorts started between 1996 and And although the 2000 cohort had an average follow-up period of only 2.5 years, live birth rates are already better than those of the earlier cohorts of From the 1998 cohort onward we see a CLBR of approximately 60%. The cohort method also enables us to show diminishing multiple birth rates as well as the increased influence of cryopreservation, as a consequence of the increasing application of single ET. For the most common IVF/ICSI indications the CLBRs vary from 56% to 63% and do not appear significantly different. This was also observed by Olivius et al. (15). In our study group the highest score was obtained in the subgroup of unexplained infertility in combination with donor semen (74.2%). This group was considered as part of the Fertility and Sterility 105

8 FIGURE 4 Relation of the observed cumulative live birth rate and the overestimation factor. Results after a follow-up period of 3 cycles are shown by the red line; a follow-up of 5 or more cycles is represented by the blue line. Data points refer to Table 5. A the data from this study. unexplained infertility group because all included patients had at least 12 insemination cycles before starting IVF. The high CLBR for these women might be explained by a relative low frequency of female subfertility in combination with good-quality donor semen. With the increase of the women s age at treatment onset the chances of getting pregnant after IVF/ICSI treatment go down significantly (P.01). At the same time chances of early pregnancy loss increase. Nevertheless, in this study the CLBR for women years of age was still 31.3%. Earlier observations showed similar results (8). It is our policy to transfer a limited number of embryos, which makes excessive stimulation unnecessary. This is reflected by the average numbers of oocytes per retrieval and the average number of embryos per transfer; in this study 8.6 and 2.0, respectively. Nevertheless during this study we observed 24.8% twins and 0.9% triplets. Double ET appears to be responsible for half the number of triplets. No selective fetal reduction was performed. Although the birth results presented in this study were high compared with other publications from this period (Table 5), the average multiple birth rate is similar to the mean value observed in 2000 in the whole of Europe. The triplet rate is lower than that published in the last available European report of Assisted Reproduction Technology registries (3). The numbers of twins and triplets reported in our study were 24.8% and 0.9% respectively, whereas the European data showed an average of 24.4% twin births and 2.0% triplet births. Moreover, the multiple birth rate in this study decreased from approximately 30% for the cohorts started between 1996 and 1999 to approximately 20% for the 2000 and 2001 cohorts. Nevertheless, a further decrease in future remained an absolute priority. The major challenge in artificial reproductive technology is to obtain the highest possible birth rates together with the lowest possible numbers of multiple births. To reduce the number of multiples we started in 2002 a protocol for single embryo transfer (SET). In 2003, 29% of all transfers in our center, including the transport clinics, were SETs. The multiple pregnancy rate for fresh stimulated cycles as well as after cryopreservation decreased to 10% and is currently the lowest in The Netherlands (19). The ongoing pregnancy rate per stimulated cycle initiated decreased from around 25% to approximately 20%. Of course it is our concern that the reduction of pregnancy chances remain restricted to an absolute minimum. We believe that embryo cryopreservation can compensate for the decreased pregnancy rates, because 106 Witsenburg et al. Cohort follow-up of IVF/ICSI patients Vol. 84, No. 1, July 2005

9 we saw that the overall ongoing pregnancy rate, with the cryopreservation results included, was hardly affected (between 26% and 28%) after the introduction of the SET protocol (19). The recently proposed BESST as the standard to present the successes obtained with assisted reproduction technology (17) is in our opinion less informative than the cohort method. BESST has the disadvantage that it provides no information about the risk of multiple birth rates. The correlation between BESST and the multiple birth rate is very weak. Even when using the cohort method for determining cumulative birth rates, it remains very difficult to compare results between centers or countries. The outcome is influenced by several variables, such as the transfer policy concerning the number of embryos and the definition of multiple rate (with or without fetal reduction). Moreover, the percentage of multiples considered to be acceptable differs between countries. In conclusion, it can be stated that the cohort follow-up method for determining the crude CLBR is very informative for the patient. This procedure can be used to show the singleton birth rate as well as the risk for a multiple birth. It does not overestimate the success rate and provides a comparison between patient groups and subgroups. Yearly cohorts can be used to trace the effects of changes in treatment policies. Moreover, by defining all kinds of cohorts, the method is easily applicable for comparison between these cohorts. It shows not only the final success rates but also the proportion of patients ending treatment without success. This is in contrast with the popular and widely used life table analysis of the cumulative success rate, which, depending on patients as well as center characteristics, provides us with a considerable overestimation. REFERENCES 1. Steptoe P, Edwards R. Birth after reimplantation of a human embryo. Lancet 1978;2: Assisted reproductive technology in the United States: 1999 results generated from the American Society for Reproductive Medicine/ Society for Assisted Reproductive Technology Registry. Fertil Steril 2002;78: Assisted reproductive technology in Europe, Results generated from European registers by ESHRE. Hum Reprod 2004;19: Hurst T, Lancaster P. Assisted Conception Australia and New Zealand 1999 and Assisted Conception Series No. 6. Sydney: Australian Institute of Health and Welfare National Perinatal Statistics Unit; Bachelot A, Pouly JL, Devecchi A, Quenard A, de Mouzon J FIVNAT general balance. Contracept Fertil Sex 1998;26: Dor J, Seidman DS, Ben-Shlomo I, Levran D, Ben-Rafael Z, Mashiach S. Cumulative pregnancy rate following in-vitro fertilisation: the significance of age and infertility reason. Hum Reprod 1996;11: Alsalili M, Yuzpe A, Tummon I, Parker J, Martin J, Daniel S, et al. Cumulative pregnancy rates and pregnancy outcome after in-vitro fertilisation: 5000 cycles at one centre. Hum Reprod 1995;10: Engmann L, Maconochie N, Bekir JS, Jacobs HS, Tan SL. Cumulative probability of clinical pregnancy and live birth after a multiple cycle IVF package: a more realistic assessment of overall and age-specific success rates? Br J Obstet Gynaecol 1999;106: de Jong D, Eijkemans MJC, Beckers NGM, Pruijsten RV, Fauser BCJM, Macklon NS. The added value of embryo cryopreservation to cumulative ongoing pregnancy rates per IVF treatment: is cryopreservation worth the effort? J Assist Reprod Genet 2002;12: Kaplan EL, Meier P. Non-parametric estimation from incomplete observation. J Am Stat Assoc 1958;53: De Mouzon J, Rossin-Amar B, Bachelot A, Renon C, Devecchi A. FIVNAT. Influence of attempt rank in in vitro fertilisation. Contracept Fertil Sex 1998;26: Fukuda J, Kumagai J, Kodama H, Murata M, Kawamura K, Tanaka T. Upper limit of the number of IVF-ET treatment cycles in different age groups, predicted by cumulative take-home baby rate. Acta Obstet Gynaecol Scand 2001;80: Osmanagaoglu K, Tournaye H, Camus M, Vandervorst M, Van Steirteghem A, Devroey P. Cumulative delivery rates after intracytoplasmatic sperm injection: 5 year follow-up of 498 patients. Hum Reprod 1999;14: Stolwijk AM, Wetzels AMM, Braat DDM. Cumulative probability of achieving an ongoing pregnancy after in vitro fertilisation and intracytoplasmatic sperm injection according to a women s age, subfertility diagnosis and primary or secondary subfertility. Hum Reprod 2000;15: Olivius K, Friden B, Lundin K, Bergh C. Cumulative probability of live birth after three in vitro fertilization/intracytoplasmatic sperm injection cycles. Fertil Steril 2002;77: Land JA, Courtar DA, Evers JLH. Patient dropout in an assisted reproductive technology program: implications for pregnancy rates. Fertil Steril 1997;68: Min JK, Breheny SA, MacLachlan V, Healy DL. What is the most relevant standard of success in assisted reproduction? The singleton, term gestation, live birth rate per cycle initiated: the BESST endpoint for assisted reproduction. Hum Reprod 2004;19: Kovacs GT, Maclachlan V, Brehny S. What is the probability of conception for couples entering an IVF program? Aust N Z J Obstet Gynaecol 2001;41: Dutch Society for Obstetrics and Gynaecology. Voorlichting, IVF resultaten, IVF-cyfers per kliniek Available at: files/ivfcijfers2003perkliniek.pdf. Accessed November Osmanagaoglu K, Tournaye H, Kolibianakis E, Camus M, Van Steirteghem A, Devroey P. Cumulative delivery rates after ICSI in women aged 37 years. Hum Reprod 2002;17: Osmanagaoglu K, Vernaeve V, Kolibianakis E, Tournaye H, Camus M, Van Steirteghem A, et al. Cumulative delivery rates after ICSI treatment cycles with freshly retrieved testicular sperm: a 7-year follow-up study. Hum Reprod 2003;18: Naaktgeboren N, Dieben S, Heijnsbroek I, Verburg H, Van der Westerlaken L. Embryo transfer, easier said than done. Embryo transfer (ET) technique, a highly underestimated part of the IVF/ICSI procedure. Fertil Steril 1998;70(Suppl 1):352. Fertility and Sterility 107