Human Reproduction vol.12 no.ll pp.2402-2407, 1997 Natural cycle in-vitro fertilization in couples with unexplained : impact of various factors on outcome

F.Zayed1'3, E.A.Lenton1'2 and I.D.Cooke2 The first live birth following IVF occurred in 1978 and was a consequence of IVF performed in the natural cycle 'Sheffield Fertility Centre, 26 Glen Road, Sheffield S7 IRA and 2University Department of Obstetrics and Gynaecology, of a woman with tubal infertility (Edwards et al, 1980). Downloaded from https://academic.oup.com/humrep/article/12/11/2402/664697 by guest on 30 September 2021 Jessop Hospital for Women, Sheffield S3 7RE, UK This success encouraged a number of groups to attempt NIVF, but they experienced difficulties (Johnston et al, 3To whom correspondence should be addressed at: Department of Obstetrics and Gynaecology, Jordan University of Science and 1981; Jones et al, 1982). NIVF was quickly abandoned in Technology, P.O. Box 962106, Amman-11196, Jordan favour of stimulated IVF (SIVF), which yielded higher pregnancy rates as a consequence of transferring several This study evaluated outcome in 117 couples with un- embryos (Wood et al, 1985; Testart et al, 1986). However, explained infertility who underwent 162 attempts at recently interest in NIVF has revived because of concerns natural cycle in-vitro fertilization (NIVF) between 1991 surrounding ovarian stimulation. These include ovarian and 1993. An egg was obtained in 138 cycles and a hyperstimulation syndrome, multiple pregnancies (Rizk single embryo was transferred in 89 cycles. There were 16 et al, 1991; Tan et al, 1992), a possible decrease in implantations (four biochemical pregnancies, three clinical endometrial receptivity (Paulson et al, 1990), the emotional abortions and nine live births). The implantation rate per 'roller coaster' of IVF- (Claman et al, embryo was 16/89 (18.0%), which translated into a live 1993), a suggested increased risk of developing ovarian birth rate per egg collection of 9/138 (6.5%). The impact cancer (Whittemore et al, 1991; Spirtas et al, 1993), factors that were assessed included oocyte quality, sperm legal and ethical dilemmas associated with storage and quality, embryo quality and woman's age. The outcome disposal of surplus embryos and the rising cost of stimulation measures used were fertilization/inseminated egg and as a consequence of the introduction of recombinant implantation/replaced embryo. All embryo transfers were drugs. of single embryos. We conclude that, in couples with Ranoux et al (1988) reported a NIVF of unexplained infertility, outcome following NIVF is affected 20% per embryo transfer that later increased to 32% in an by both egg and sperm quality and by the age of the expanded series (Foulot et al, 1989). Svalander et al. (1991), woman. Embryo quality was independent of the above Lenton et al. (1992) and Paulson et al. (1992) all reported factors but was also critical for successful implantation. reasonable pregnancy rates following NIVF which Claman Key words: implantation/in-vitro fertilization/natural cycle/ et al (1993) and DeLauretis et al (1994) were unable to unexplained infertility confirm. Fertilization rates in NIVF studies have been reported to vary from 50 to 90%, depending on whether the spontaneous luteinizing hormone (LH) surge was used to time egg recovery (Lenton et al, 1992; Taymor et al, 1992; DeLauretis et al, Introduction 1994) or human chorionic gonadotrophin (HCG) was given As the name implies, the mechanism(s) resulting in infertility (Muasher et al, 1980; Foulot et al, 1989; Svalander et al, in those couples designated as having unexplained infertility 1991; Paulson, 1993; Claman et al, 1993; DeLauretis et al, are unknown. It can be speculated that there may be occult 1994; Scarduelli et al, 1994). Few studies have described problems in either the oocyte or the spermatozoon, leading to outcomes in patients selected by type of infertility (Fahy et al., fertilization failure or dysfunctional embryos, or at the level 1995) or have assessed cost-effectiveness and other factors of the endometrium, resulting in implantation failure. Conven- (Daya et al, 1995). In the UK, NIVF is now only rarely tional infertility investigations consisting of a performed as a direct consequence of the negative impact of and tests to assess ovulatory status and tubal patency are the inevitably lower pregnancy outcomes on overall clinic unable to detect subtle functional disorders. performance reflected in comparative data published annually Natural cycle in-vitro fertilization (NIVF) has been used to by the Human Fertilisation and Embryology Authority (HFEA, treat unexplained infertility, but the pregnancy rates are rela- 1995 and 1996 Patient Guides). tively low (Lenton et al, 1992). Despite this, NIVF is a good The following retrospective analysis of NIVF undertaken in model for assessing fertilization and embryo development couples with unexplained infertility aimed to study the impact under spontaneous or natural cycle conditions. Information of various gamete-associated parameters on implantation rates gained from the analysis of such studies may yield insights into in the hope that this would give some insight into the factors the importance of the contribution of the egg, spermatozoon and that may be important for success. embryo to successful pregnancy outcome.

2402 © European Society for Human Reproduction and Embryology Natural cycle IVF in unexplained infertility

Table I. The impact of female age on the proportion of oocytes suitable for insemination, the percentage of oocytes which fertilized and the implantation rate (human chorionic gonadotrophin >10 U/l) following single embryo transfer in the natural cycle relative to the implantation rate per egg collection cycle

Female All cycles Oocytes Fertilization Implantation Implantation age with suitable for per inseminated per replaced per cycle with (years) oocytes (%) insemination (%) oocyte (%) embryo (%) oocytes (%)

24-29 22 91 85 17.6 13.6 30-35 73 96 73 19.1 12.3 36-40 35 91 69 19.0 11.4 41-44 8 75a 67 0 0

aThere were significantly fewer (P < 0.05) suitable oocytes retrieved from older women relative to those =£40 years. Downloaded from https://academic.oup.com/humrep/article/12/11/2402/664697 by guest on 30 September 2021

Methods and materials of NIVF and the quality of both sperm and eggs were analysed for their impact on fertilization, as well as for embryo development and Subjects implantation. The differences were considered significant at a level The Sheffield Fertility Centre has extensive experience of NIVF. This of P < 0.05. study is a retrospective analysis of all cases of unexplained infertility treated by NIVF between 1991 and 1993. Unexplained infertility was defined according to the following criteria: duration of infertility ^2 Results years, regular menstrual cycles (25-34 days), patent tubes diagnosed The analysis included 117 couples studied during 162 NIVF by laparoscopy or hysterosalpingography and a normal semen analysis using local criteria of concentration >20X 106 spermatozoa/ cycles. Seven cycles were cancelled due to poor follicular ml, motility >30% (grades I+II), normal morphology >25% and growth or dysfunctional ovulation, and in 10 cycles the women antisperm antibodies <25%. The age of the female partners ranged ovulated spontaneously prior to egg collection. Eggs were from 24 to 44 years and that of the male partners from 22 and 49 obtained in 138 of the 145 cycles (93.2%) undergoing follicular years; duration of infertility was from 2 to 19 years. aspiration; 128 of the eggs obtained were normal (92.8%) and were inseminated and 94 (73.4%) fertilized with two pronuclei. Natural cycle IVF Of these, 89 single embryos were replaced, resulting in 16 All the IVF cycles were completely natural, clomiphene citrate was implantations (four biochemical pregnancies, three clinical not used and all egg collections were performed following detection of the spontaneous LH surge. Blood was taken for base line plasma abortions and nine live births). The overall implantation rate LH and follicle stimulating hormone (FSH) concentrations on day 2 per cycle was 16/162 (9.9%), while the implantation rate per and then twice daily from day 9 of the cycle for measurement of cycle with an egg was 16/138 (11.6%) and the implantation oestradiol and to detect the onset of the LH surge. The precise time rate per single embryo replaced was 16/89 (18.0%). The live of onset of the LH surge was calculated by interpolation from tables birth rate per cycle with egg collection was 9/138 (6.5%). derived from LH profiles obtained during earlier studies of NIVF (see Figs. 1, 2 and 3 in Lenton et al., 1992). Egg collection was Female age ideally timed to be ~34—36 h from the onset of the spontaneous LH To study the impact of female age, patients were divided into surge and was performed using transvaginal ultrasound (Ramsewak et al., 1990). Measurements of LH and oestradiol were performed four groups: 24-29, 30-35, 36-40 and 41^4 years of age using enzyme immunoassay (Serozyme; Serono Diagnostics Limited, (Table I). The proportion of oocytes suitable for insemination Surrey, UK). All semen samples for IVF were prepared by Percoll (i.e. normal oocytes) was constant at 91-96%, except in women density centrifugation. Oocytes were conventionally fertilized in vitro aged >40 years, when it declined to 75% (P < 0.05). and single embryos were transferred 2-3 days after follicle aspiration. Fertilization rates also declined slowly but steadily with Luteal support was with dydrogesterone (30 mg daily, Duphaston; increasing age, from 85% in the youngest group to 67% in Solvay Healthcare Ltd, Southampton, UK). Implantations were identi- women >40 years. Surprisingly, implantation rates per embryo fied by serially rising HCG concentrations and later confirmed as a remained constant up to the age of 40 years, but no implanta- clinical pregnancy when an intrauterine gestation sac was seen on tions were achieved in the eight women aged 2=41 years in ultrasound. Some implantations resulted in a biochemical pregnancy, this study. The small changes in fertilization rates, even under which was defined as rising HCG (>10 U/l) with 3=5 days menstrual delay but where no gestation sac was seen. This study did not set the age of 40 years, were reflected in the overall outcomes out to examine early pregnancy wastage, and indeed the numbers (implantation rate per egg collection), which again declined were too small for this to be meaningful, so for the purposes of the slowly but steadily with advancing age. comparison of gamete characteristics, only a single determinant, that of implantation irrespective of whether the pregnancy continued, was Oocyte quality assessed. Further, as only one embryo was ever replaced per cycle, Oocytes were collected in 138 cycles. They were scored by the implantation rate per embryo transfer was the same as the assessing the cumulus mass and corona radiata and were implantation rate per embryo. considered good if there was a loosely aggregated granulosa, Statistical methods expanded cumulus and corona radiata, indicating a mature Statistical analysis of discrete variables was by %2 analysis with oocyte; others were classified as poor or damaged/abnormal. Fisher's exact test where applicable. Female age, number of attempts Damaged or morphologically abnormal oocytes were not 2403 F.Zayed, E.A.Lenton and I.D.Cooke

Table II. The impact of oocyte quality on the percentage of oocytes which fertilized and the implantation rate following single embryo transfer in the natural cycle relative to the implantation rate per egg collection cycle

Oocyte All cycles Fertilization Implantation Implantation quality with per inseminated per replaced per cycle with oocytes (%) oocyte (%) embryo (%) oocytes (%)

Good 104 78 17.9 13.5 Poor 24 54a 18.2 8.3 Abnormal 10 NI

aThere was a significantly lower (P < 0.01) fertilization rate with 'poor' eggs. NI = not inseminated. Downloaded from https://academic.oup.com/humrep/article/12/11/2402/664697 by guest on 30 September 2021

Table III. The impact of sperm quality on the proportion of morphologically normal oocytes (good quality eggs), the percentage of oocytes which fertilized and the implantation rate following single embryo transfer in the natural cycle relative to the implantation rate per egg collection cycle

Sperm All cycles Oocytes Fertilization Implantation Implantation quality8 with suitable for per inseminated per replaced per cycle with oocytes (%) insemination (%) oocyte (%) embryo (%) oocytes (%)

NI 56 95 79 17.5 12.5 N2 52 92 75 20.6 13.5 N3 30 90 59b 13.3 6.7

aMen were arbitrarily classified into three groups according to their pre-treatment semen analysis: NI = progressive motility >50%, normal morphology >50%; N2 = progressive motility >40%, normal morphology >25%; N3 = progressive motility >30%, normal morphology >25%. ^here was a significantly lower (P < 0.05) fertilization rate using spermatozoa from semen samples designated N3 relative to those from NI and N2 samples.

>30%, normal morphology >25%). Sperm concentration was Table IV. The impact of embryo quality on implantation rate per single >20Xl06/ml and antisperm antibodies <25% in all groups. embryo transfer The semen samples from group NI met the World Health Embryo No. of cycles Implantation Organization (WHO, 1987) criteria for normal semen para- a grade with embryos per embryo (%) meters. Group N3 met the WHO (1992) criteria with respect Gl 24 25.0 to motility but not morphology (>50%), although stricter G2 13 23.1 classifications of morphology yielding lower normal para- G3 39 17.9 meters have recently been recommended (Kruger et al, 1986). G4 5 0.0 G5 8 0.0 Coincidentally, the incidence of damaged/abnormal eggs G6 5 NR unsuitable for insemination was higher in N3 couples (10%) than in either NI or N2 (mean 6.5%). Even after excluding NR = not replaced. aEmbryos were graded morphologically before replacement as good (Gl), the influence of abnormal eggs, fertilization rates (79 and reasonable/good (G2), reasonable (G3), reasonable/poor (G4), poor (G5) and 75%) and implantation rates (17 and 19%), although uniform very poor (G6). for both NI and N2 respectively, were slightly reduced in the N3 group (59%, P < 0.05 and 13%, not significant, inseminated. A total of 104 oocytes obtained were classified respectively) (Table III). As with female age and oocyte as good quality (75%), 24 (17%) as poor quality and 10 (7%) quality, the lower proportion of fertilizable eggs coupled with as abnormal eggs (Table II). Fertilization occurred in 81/104 lower fertilization and embryo implantation rates effectively (78%) of the 'good' eggs and in 13/24 (54%) of the 'poor' halved the final outcome (implantation per egg collected) in eggs (P < 0.01). Again, implantation rates per embryo were N3 couples. not influenced by egg quality and were constant at ~18%. However, the impact of the reduced fertilization rates effec- tively reduced the overall outcome from 13.5 to 8.3% with Embryo quality the 'good' and 'poor' eggs respectively. To study the impact of embryo quality on implantation, the embryos were graded morphologically before replacement as Sperm quality good (Gl), reasonable/good (G2), reasonable (G3), reasonable/ To assess the impact of sperm quality, the male partners were poor (G4), poor (G5) and very poor (G6). This last group of arbitrarily classified into three groups according to their pre- embryos was not replaced. Ninety-four embryos were obtained treatment semen analysis as NI (progressive motility >50%, but only 89 embryos were transferred in 89 cycles because normal morphology >50%), N2 (progressive motility >40%, five embryos were graded very poor (G6) (Table IV). Both normal morphology >25%) and N3 (progressive motility Gl and G2 embryos displayed a high implantation rate (25 2404 Natural cycle IVF in unexplained infertility

and 23% respectively), with G3 embryos intermediate (18%). investigations are normal and so it is necessary to postulate No implantations were, however, recorded with either G4 that there may be as-yet-unidentified factors associated with or G5 embryos, although the numbers of these embryos either the egg, spermatozoon, embryo or uterus that could be were small. causal. The interaction between egg and spermatozoon can be studied by assessing fertilization rates, while the interaction Repeated cycles of NIVF between embryo and uterus (endometrium) is studied via A small number of couples (n = 38) elected to have a second implantation rates. NIVF cycle during the study period for a variety of reasons. Analysing the impact of female age on the percentage of In general, these were either because of failure to recover an morphologically acceptable eggs, fertilization and implantation egg in the first attempt (9%), or because they conceived in the rates, the above results suggested that only the oldest women first attempt but the pregnancy either did not continue or they were likely to have eggs that were unsuitable for insemination wished to have a second child (9%), or because although they but, irrespective of this, fertilization rates per inseminated failed to conceive in the first cycle they were committed to egg declined steadily with increasing female age (Table I). Downloaded from https://academic.oup.com/humrep/article/12/11/2402/664697 by guest on 30 September 2021 the concept of NIVF and wanted to try again. Not unexpectedly, However, provided fertilization occurred, the resulting embryos in this selected and highly motivated subgroup, implantation all had an equal chance of implanting. No implantations rates per single replaced embryo were 15% (first attempt) and occurred in the small group of women aged >40 years, but 31% (second attempt), giving implantation rates per egg since only four of these cycles reached embryo transfer, this collection cycle of 9 and 15% respectively. is to be expected. There is no obvious explanation for the decline in fertilization rates, nor indeed did they reach statistical significance, but they are in line with other findings that female Discussion fertility declines with increasing age (Collins and Rowe, 1989). Relatively few studies describing treatment with NIVF have Surprisingly, considering that the oocytes were graded been reported. Most studies are limited by attempts to morphologically rather than functionally, a correlation was manipulate the timing of egg collection by administration of seen between fertilizing ability and egg quality. Fertilization HCG; these cycles are not strictly NIVF but merely unstimu- rates were significantly lower (P < 0.01) in the eggs classified lated IVF, and may not be directly comparable. In this as 'poor', although they were still suitable for insemination. retrospective study, we tried to assess those factors which Again, provided the egg fertilized normally, the resulting could be expected to influence outcome in couples with embryo's potential to implant was independent of egg quality. unexplained infertility but, in common with most other NIVF One explanation is that the morphological egg grading 'over- analyses, we experienced difficulties in obtaining sufficient calculated' the incidence of functionally incompetent eggs by data on pregnancy outcomes for valid statistical analyses. a factor of two. Thus, ~50% of the eggs classified as 'poor' Although 162 cycles were eligible for inclusion, only 138 may actually have been normal, and they fertilized and the successfully yielded eggs. In seven cases (4.3%), the cycle resulting embryos implanted at the normal rate. The other was cancelled due to suboptimum folliculogenesis, but whether 50% were definitely abnormal and failed to fertilize. Overall this was a sporadic or a persistent problem associated with the treatment outcomes were significantly influenced by the lower infertility is unknown. In 10 cases (6.2%), the follicle ruptured fertilization rates, with the 19% of cycles yielding 'poor' eggs just before egg recovery. This was due either to miscalculating having only half the per-cycle chance of a pregnancy than the LH surge-egg collection interval or to an abnormality of cycles with 'good' eggs. the cycle resulting in premature ovulation. At follicle aspiration Analysis of the impact of sperm quality, as assessed by pre- no egg was obtained in a further seven cases (4.3%), despite treatment semen analyses, also demonstrated a small but many flushes of the follicle. It is possible that some of these significant effect on fertilization rates: 41% of the men with a follicles did not contain an egg (Ashkenazi et al., 1987) or borderline-normal semen analysis (N3) failed to fertilize the that there was again an unappreciated LH timing problem. single egg available compared with only 23% of the clearly Daya et al. (1995) described the outcome of 240 NIVF cycles normal men (Nl and N2 combined). Implantation rate per (all infertility cases), and in their study only 65% of cycles embryo was not significantly different within any of the three progressed to oocyte retrieval compared with 85% in our male groups but overall, pregnancy outcomes per egg collection study. As with other forms of IVF, a small cancellation rate is cycle were, as seen above, clearly affected by the lower N3 inevitable, but with NIVF in particular, there is a significant fertilization rate. It is perhaps surprising that sperm quality chance of failing to recover the only available egg, resulting had any impact at all on outcome because not only does a of course in cycle termination. There is no evidence from semen analysis describe sperm appearance, not sperm function, these data that the proportion of cycles which failed to yield but the pre-treatment analyses were often obtained several an egg was any higher than could be reasonably expected months prior to the IVF cycle. Furthermore, for the purposes of from the NIVF technique and, at 15% cancellation rate, was fertilization in vitro, all these men could have been considered not very different from stimulated IVF. Thus, there is no normal. It is perhaps worth pointing out that, in NIVF, failure support for the hypothesis that couples with unexplained to fertilize the single egg is an event which terminates that infertility (with regular ovulatory cycles) experience more treatment attempt, but it does not necessarily follow that cycle dysfunction than other regularly cycling women. fertilization would fail again on another occasion in that same In couples with unexplained infertility, standard infertility couple (Rowlands et al., 1994). One of the advantages of 2405 F.Zayed, E.A.Lenton and I.D.Cooke stimulated IVF is that, with several eggs available, failure of From the above results it is possible that, with careful patient some of the eggs to fertilize still leaves embryos to replace. selection (women <40 years, completely normal male charac- The overall fertilization rate obtained here was 69%, which teristics) and better methods of assessing gamete competence, was not much different from overall stimulated IVF fertiliza- satisfactory pregnancy and live birth rates could be easily and tion rates. cheaply achievable. The results described in this study failed to show any impact of egg quality, sperm quality or female age (except >40 years), provided fertilization occurred, on the potential of an embryo Acknowledgements to implant. However, it was observed that the morphological We would like to express our gratitude to all the staff employed at grading of the embryo at the time of replacement did correlate the Sheffield Fertility Centre during the time period when these patients were treated, in particular Drs Anju Kumar, Sohani Verma, with implantation. Some 81% of embryos were graded GI- Nicky Monks and Karen Turner. We would also like to thank Steven GS, the first three best grades, and these all showed an Evans for performing the statistical analyses. equivalent probability of implanting. The corollary is that Downloaded from https://academic.oup.com/humrep/article/12/11/2402/664697 by guest on 30 September 2021 ~75% of the G1-G3 embryos with apparently 'good' potential also failed to implant and a further 19% of all the embryos References (G4-G6) were also unable to generate a pregnancy. As with Ashkenazi, J., Feldberg, D., Shelf, M. et al. (1987) Empty follicle syndrome: an entity in the etiology of infertility of unknown origin or a phenomenon egg and sperm assessment, embryo gradings just prior to associated with purified follicle-stimulating therapy. Fertil. Steril., 48, replacement provide only a crude measure of an embryo's 152-154. later developmental capacity. Possibly, many embryos failed Claman, P., Domingo, M., Gamer, P. et al. (1993) Natural cycle in-vitro fertilization-embryo transfer at the University of Ottawa: an inefficient to develop to blastocyst, a few may have been replaced into therapy for tubal infertility. Fertil. Steril, 60, 298-302. a uterus with an unreceptive endometrium and a few may have Collins, J.A. and Rowe, T.C. (1989) Age of the female partner is a prognostic been lost during embryo transfer itself. Finally, it is worth factor in prolonged unexplained infertility: a multicentre study. Fertil. emphasizing that the maximum implantation rate per IVF- Steril, 52, 15-20. Daya, S., Gunby, J., Hughes, E.G. et al (1995) Natural cycles for in-vitro generated embryo, even under carefully selected conditions, fertilization: cost-effectiveness analysis and factors influencing outcome. is likely to be no more than 25% and even then not all of Hum. Reprod., 10, 1719-1724. these implantations will progress to a live birth. If each DeLauretis, L., Scardulli, C, Bailo, U. et al. (1994) IVF in natural cycles: stimulated IVF embryo were to have a similar 25% implantation our experience. Hum. Reprod., 9 (Suppl. 4), 131. Edwards, R.G., Steptoe, PC. and Purdy, J.M. (1980) Establishing full-term potential, then simultaneous replacement of two embryos human pregnancies using cleaving embryos grown in-vitro. Br. J. Obstet. would yield a pregnancy rate of 44% per embryo transfer, Gynaecol, 87, 737-756. three such embryos replaced together would increase this to Fahy, U.M., Cahill, D.J., Wardle, P.G. and Hull, M.G.R. (1995) In-vitro fertilization in completely natural cycles. Hum. Reprod., 10, 572-575. 58% (simple binomial expansion). Since pregnancy rates of Foulot, H., Ranoux, C, Dubuisson, J.B. et al. (1989) In-vitro fertilization this order are seldom seen following assisted conception, without ovarian stimulation: a simplified protocol applied in 80 cycles. except perhaps with donated gametes, we must conclude Fertil. Steril, 52, 617-620. that stimulated IVF-generated embryos have relatively low Human Embryo and Fertilisation Authority (1995, 1996) The Patients' Guide to DI and IVF Clinics, Paxton House, 30 Artillery Lane, London. implantation potentials. Johnston, I., Lopata, A., Spiers, A. et al. (1981) In-vitro fertilization: the Clearly, many couples in this series had little chance of challenge of the eighties. Fertil. Steril, 36, 699-706. conceiving following NIVF, but the importance of patient Jones, H.W., Jones, G., Andrews, M. et al. (1982) The programme for in- vitro fertilization at Norfolk. Fertil. Steril, 38, 14-21. selection is reflected in the improved outcome in the small Kruger, T.F., Menkveld, R., Stander, F.S. et al (1986) Sperm morphologic group of couples who attempted NIVF for the second time. features as a prognostic factor in in-vitro fertilization. Fertil Steril, 46, An implantation rate of 15% per egg collection cycle is 1118-1123. not dissimilar to rates obtained after stimulated intrauterine Lenton, E.A., Cooke, I.D., Hooper, M. et al. (1992) In-vitro fertilization in the natural cycle. Balliere's Clin. Obstet. Gynaecol, 6, 229-245. insemination (IUI) (multiple eggs) or stimulated IVF (multiple Muasher, S.J., Kruithoff, C, Webster, S. et al. (1980) Natural cycle in-vitro embryos), but costs considerably less. Those patients with a fertilization (IVF): a simplified treatment method. Fertil. Steril, 33, 26-27. poor prognosis for NIVF still have recourse to treatment Paulson, R.J. (1993) Natural cycle in-vitro fertilization. Infertil Reprod. Med. involving ovarian stimulation. Clin. North Am., 4, 653-665. Paulson, R.J., Sauer, M.V. and Lobo, R.A. (1990) Embryo implantation after In conclusion, in couples with unexplained infertility, the human in-vitro fertilization: importance of endometrial receptivity. Fertil. outcome following NIVF is marginally affected by both egg Steril, 53, 870-874. and sperm quality and by the age of the woman, principally Paulson, R.J., Sauer, M.V., Francis, M.M. et al. (1992) In-vitro fertilization in unstimulated cycles: the University of South California experience. via alterations in fertilization rates. Embryo implantation Fertil. Steril, 57, 290-293. potential is independent of the above factors but is also critical Ramsewak, S.S., Cooke, I.D., Li, T.C. et al. (1990) Are factors that influence for pregnancy to occur. As fertilization has such a major oocyte fertilization also predictive? An assessment of 148 cycles of in-vitro impact on NIVF outcomes, it is clear that couples with male fertilization without gonadotrophin stimulation. Fertil. Steril, 54, 470-474. Ranoux, C, Foulot, H., Dubuisson, J.B. et al. (1988) Returning to spontaneous factor infertility should not be recruited for this treatment, cycles in in-vitro fertilization. J. In Vitro Fertil. Embryo Transfer, 5, 304. but it remains to be established whether women with tubal Rizk, B., Doyle, P., Tan, S.L. et al. (1991) Perinatal outcome and congenital infertility will respond similarly to couples with unexplained malformations in IVF babies. Hum. Reprod., 6, 1259-1264. infertility. Daya et al. (1995) claimed that, in spite of their Rowlands, D.J., McDermott, A. and Hull, M.G.R. (1994) The prognosis for assisted conception treatment after unexpected failure of fertilization in vitro: low clinical pregnancy rate and very low live birth rate per cycle a comparative study. Hum. Reprod., 9, 2287-2290 (3.8%), NIVF was still more cost-effective than stimulated IVF. Scardulli, C, Caccamo, A., Bailo, U. et al. (1994) Does HCG improve 2406 Natural cycle IVF in unexplained infertility

pregnancy rate in IVF in natural cycles? Hum. Reprod., 9 (Suppl. 4), 131-132. Spirtas, R., Kaufman, S.C. and Alexander, N.J. (1993) Fertility drugs and ovarian cancer: red alert or red herring? Fertil. SteriL, 59, 291-293. Svalander, P., Green, B., Haglund, K. et al. (1991) Natural versus stimulated cycles in IVF-ET treatment for tubal factor infertility. Hum. Reprod., 6 (Suppl. 1), 101. Tan, S.L., Doyle, P., Campbell, S. et al. (1992) Obstetric outcome of in-vitro fertilization pregnancies compared with normally conceived pregnancies. Am. J. Obstet. Gynecol., 167, 778-784. Taymor, M.L., Ranoux, C.J. and Gross, G.L. (1992) Natural oocyte retrieval with intravaginal fertilization: a simplified approach to in-vitro fertilization. Obstet. Gynecol., 80, 888-891. Testart, J., Belaisch-Allart, J. and Frydman, R. (1986) Relationship between embryo transfer results and ovarian response and in-vitro fertilization rate:

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Received on November 11, 1996; accepted on August 13, 1997

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