Reproductive Unit, Department of Obstetrics and Gynaecology, University Medical Centre Ljubljana, lajmerjeva 3, 1000-Ljubljana, Slovenia
1 To whom correspondence should be addressed. e-mail: irma.virant{at}kclj.si
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: blastocysts/ICSI/spermatozoa/testis
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Abnormal sperm in terms of concentration, morphology and motility may manifest a negative effect on preimplantation embryo development to the blastocyst stage (Janny and Ménézo, 1994; Shoukir et al., 1998
; Griffiths et al., 2000
; Dumoulin et al., 2001
; Miller and Smith, 2001
). Additionally, the ICSI procedure in itself contributes to a reduced capacity of blastocyst formation in comparison with classical IVF (Griffiths et al., 2000
; Dumoulin et al., 2001
).
The source and maturity of sperm, most likely to be indicative of the severity of spermatogenic disorders, affect the rate of blastocyst formation and blastocyst implantation. It has been reported that sperm from non-obstructive azoospermic subjects, when utilized for ICSI, result in embryos that progress to the blastocyst stage at a lower rate than from obstructive azoospermic subjects and from ejaculated sperm (Balaban et al., 2001). Round spermatid injection is associated with a significantly lower embryo development rate and a significantly higher developmental arrest rate, when compared with the injection of testicular sperm (Balaban et al., 2000
; Vicdan et al., 2001
). It has been reported that pronuclear morphology is correlated with chromosomal complement, and impacted upon by the sperm source (Kahraman et al., 2002
).
Silber et al. (2002) found a higher rate of chaotic mosaicism in embryos derived from TESEICSI than in those derived from ICSI with ejaculated sperm. The difference was highly significant. It has been found (Obasaju et al., 1999
) that paternal factors, which are likely to derive from the centrosome, can contribute to embryonic numerical chromosomal abnormalities, which in turn may predispose to implantation failure. Sperm quality may adversely affect the chromosome constitution of embryos that result from ICSI (Obasaju et al., 1999
). These findings indicate the importance of, and the need for, good embryo selection after TESEICSI.
Little is known about the factors affecting embryo development to the blastocyst stage after ICSI with testicular sperm. The question of whether the use of blastocyst culture selects the best embryos after ICSI with testicular sperm and leads to a better implantation rate still remains to be answered.
The aim of this study was to find the factors affecting the developmental potential of embryos after ICSI with testicular sperm, and to evaluate the clinical role of blastocyst culture in patients with azoospermia in comparison with conventional cleaving stage embryos.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The study was randomized so that each day of TESEICSI cycles with embryos cultured for 2 days (Group 1) was followed by the day of TESEICSI cycles with embryos cultured for 5 days (Group 2). In this manner 226 cycles of ICSI with frozenthawed testicular sperm were included in the study. In 98 cycles (Group 1) ICSI-derived embryos were cultured conventionally for 2 days in the Universal IVF Medium (Medi-Cult, Denmark) and a maximum of two cleavage-stage embryos were transferred into the uterus on day 2. In 128 cycles (Group 2) embryos were cultured for 5 days in the Medium 1 and Medium 2 of Blast Assist System (Medi-Cult) and a maximum of two most developed embryosblastocysts, delayed embryosmorulae, or arrested embryoswere transferred into the uterus on day 5. Supernumerary embryos were cryopreserved. We compared the clinical results between the groups. All men gave informed consent to participate in the study. The study had been approved by the National Medical Ethics Committee.
Studied population
In this study 226 ICSI cycles with testicular sperm were performed in 154 infertile men (74 men in Group 1 and 80 in Group 2) suffering from azoospermia: 29 obstructive azoospermia (16 in Group 1 and 13 in Group 2) and 125 non-obstructive azoospermia (58 in Group 1 and 67 in Group 2). Data on the age and testicular volume were collected for all the patients. Histological diagnosis of spermatogenesis was made in 62 patients (28 in Group 1 and 34 in Group 2), evaluation of serum FSH concentration in 77 patients (48 in Group 1 and 29 in Group 2). Serum FSH concentration was defined as increased at 10 IU/l and high at
20 IU/l.
Testicular biopsy and tissue cryopreservation
In all couples ICSI was performed using frozenthawed testicular sperm. In our centre the diagnostic testicular biopsy has been followed by testicular tissue freezing to avoid possible negative effects of subsequent multiple biopsies since 1997. Moreover, with sperm cryopreservation we avoid ovarian stimulation and oocyte retrieval if no testicular sperm are retrieved.
Testicular tissue was extracted by open biopsy or aspiration. Each testicular specimen was analysed for the presence of sperm. A part of the sample was immediately fixed in the Bouins solution for histological analysis of spermatogenesis using modified Johnsens score (from score 1: Sertoli cells-only and thin epithelium, to score 10: normal spermatogenesis and thick epithelium) (Holstein et al., 1994). The remaining testicular specimen was frozen to be used in subsequent ICSI treatments. Testicular tissue was dissected, mixed with cryoprotectant solution10% glycerol in Flushing Medium (Medi-Cult), put into ampoules, and frozen automatically (MiniCool 40, Air Liquide, France) to 150°C. Then it was plunged into liquid nitrogen (196°C) and stored until thawing for ICSI. It was thawed at room temperature.
IVF
Female partners were stimulated using first a desensitizing protocol of GnRH agonist (s.c. buserelin acetate 0.6 mg once daily; Suprefact; Hoechst AG, Germany), started on day 22 of the menstrual cycle. If after 14 days serum estradiol concentrations were <40 pg/ml and no ovarian cystic structures were observed on ultrasound (US) examination, stimulation was started with 225 IU/day of hMG (Pergonal; Serono, Switzerland) or FSH (Metrodin, HP 75 IU; Serono). hCG (Pregnyl; Organon, The Netherlands) 5000 IU was administered when a leading follicle measuring >18 mm in diameter was obtained. Transvaginal ultrasound-guided aspiration of ovarian follicles was performed 36 h after hCG administration using a single lumen needle.
Oocyte and sperm preparation before ICSI
Cumuluscorona cell complexes were isolated from the follicular fluid and put into 5 ml Falcon tubes with 1 ml of Universal IVF medium (Medi-Cult; the tubes were gassed in 5% O2, 5% CO2 and 90% N2. The removal of the cells of the cumulus and the corona radiata by hyaluronidase has been described extensively elsewhere (Palermo et al., 1992; Van Steirteghem et al., 1993
). Oocytes were placed in 80 IU hyaluronidase (Type VIII; Sigma, USA) and the cells of the cumulus and the corona radiata were removed with a denudation pipette (Swemed Lab, Sweden) and washed with Flushing Medium (Medi-Cult).
After testicular tissue preparation on PureSperm (Nidacon, Sweden) discontinuous concentration gradient and washing, 5 µl droplets of sperm suspension were prepared under liquid paraffin (Medi-Cult).
ICSI procedure
Metaphase-II oocytes were placed in 5 µl droplets of Universal IVF medium under liquid paraffin (Medi-Cult). ICSI was performed by the conventional method (Van Steirteghem et al., 1993) without using polyvinylpyrrolidone (PVP). A metaphase-II oocyte was aspirated with a slight negative pressure by the holding pipette (Swemed Lab) and a single spermatozoon was injected into the ooplasm by the micro-injection pipette (Swemed Lab) under an inverted microscope (Diaphot-TMD, Nikon, Japan) equipped with a hydraulic micro-manipulator (Narishige, Japan). Before micro-injection, no special selection of sperm was performed.
Embryo culture to the cleaving stage and transfer on day 2
In each patient, all embryos were cultured in a group in 0.5 ml of Universal IVF Medium (Medi-Cult) in a double-well dish (Falcon); a maximum of two embryos were transferred into the uterus on day 2 using the TDT embryo transfer set (Prodimed, Neuilly-en-Thelle, France). Supernumerary embryos of good quality (<15 % fragmentation) were cryopreserved.
Embryo culture to the blastocyst stage and transfer on day 5
Embryos were cultured to the blastocyst stage in sequential media, Medium 1 and Medium 2 of Blast Assist System (Medi-Cult). All embryos of each patient were cultured in a group. On day 1, fertilized oocytes were transferred into 0.5 ml of fresh Medium 1 in a double-well dish (Falcon). On day 2 they were transferred into fresh Medium 2. Then embryos were transferred each day into a fresh Medium 2, and on day 5 a maximum of 2 multi-cell embryos were transferred into the uterus. On day 5 we classified embryos as most developed embryosblastocysts, delayed embryosmorulae, and arrested embryoslower than morula stage. We transferred two blastocysts into the uterus; if there were no blastocysts, we transferred the two most developed embryos that did not reach the stage of blastocystmorulae, or arrested embryos. Supernumerary blastocysts were cryopreserved.
Luteal support and follow-up of pregnancy
On the day of embryo transfer, the luteal phase support was started using oral dydrogesterone, 300 mg/day (Dabroston; BELUPA, Croatia). Biochemical pregnancy was confirmed by serum beta-hCG determination 15 days after embryo transfer. Clinical pregnancy was confirmed by US demonstration of at least one gestational sac at 6 to 7 weeks of pregnancy.
Statistical analysis
For statistical analysis the SPSS program (SPSS Inc., Chicago, Illinois, USA) was used. Differences between the groups were evaluated by MannWhitney U-test. Correlations between the clinical parameters (female age, female indications of infertility, male age, serum FSH, testicular volume, modified Johnsens score), and the developmental potential of embryos after ICSI with testicular sperm were evaluated by Spearmans correlation coefficient. Statistical significance was set at P < 0.05.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Clinical results concerning ICSI with testicular sperm are presented in Table I. The group receiving embryos on day 2 did not differ from the group receiving embryos on day 5 in the male and female age, and proportion of female indications of infertility.
|
Clinical results after day 2 transfer versus day 5 transfer
Blastocyst transfer provided a high clinical pregnancy rate per embryo transfer (55 %). After the transfer of blastocysts on day 5, pregnancy and implantation rates were significantly higher than after the transfer of embryos on day 2; the abortion rate was significantly lower (Table I).
Clinical results after embryo transfer on day 5
After prolonged culture, at least one blastocyst was transferred in 31 of the 108 (24%) ICSI cycles. In the remaining transfer cycles, embryos that did not reach the blastocyst stage were transferred: morulae in 30 (28%) cycles and arrested embryos at the lower than the morula stage in 47 (44%) cycles (Table II).
|
If only blastocysts had been transferred on day 5, the clinical pregnancy rate per started cycle would have been approximately the same as in the day 2 transfer group: 13% (17 pregnancies in 128 cycles) versus 16% (16 pregnancies in 98 cycles) (Table I).
Developmental stage of embryos on day 5
After prolonged culture, 68 of the 290 (23%) embryos reached the blastocyst stage and 54 (19%) embryos reached the morula stage, whereas 35 (12%) embryos arrested before the morula stage having more than 6 cells, and 134 (46%) embryos arrested at the 26-cell stage.
Clinical factors affecting developmental potential of embryos
There was no correlation between the female age (r = 0.083, P = 0.390), female indications of infertility (r = 0.039, P = 0.687), and the number of blastocysts in the couple. In the male partner, there was no correlation between the number of blastocysts and age (r = 0.167, P = 0.197), serum FSH (r = 0.249, P = 0.143), modified Johnsens score (r = 0.098, P = 0.504) and testicular volume (r = 0.039, P = 0.687).
The only correlation we observed was a positive correlation between the serum FSH concentration in the male partner and the number of arrested embryos that did not reach the morula stage on day 5 (r = 0.387; P < 0.05). In men with high serum FSH concentrations (20 IU/l) there was a significantly lower proportion of morulae and a higher proportion of embryos arrested before the morula stage than in patients with normal serum FSH concentrations (Table III), but there was no statistically significant difference in the proportion of blastocysts between these two groups.
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In this study, 23% of embryos developed to the blastocyst stage after ICSI with testicular sperm. From our own experience, a significantly lower proportion of embryos develop to the blastocyst stage after ICSI with testicular sperm than after ICSI with ejaculate sperm (45%) or classical IVF (60%) thus confirming the negative paternal effects on embryo development.
Some recent studies show that blastocysts may have chromosomal abnormalities. It has been shown that some chromosomally abnormal human embryos develop to the blastocyst stage (Sandalinas et al., 2001). However, in our study a high pregnancy rate per embryo transfer (55%) and a very low spontaneous abortion rate (6%) by blastocysts were obtained. Clinical pregnancies (13%) were also achieved by the transfer of morulae, although half of these pregnancies ended in a spontaneous abortion. Morulae are delayed embryos and a good percentage of these embryos should reach the blastocyst stage on day 6. Our findings fit with the observation of a lower implantation rate of the embryos reaching the blastocyst stage on day 6. After 47 transfers of embryos arrested at a lower cell-stage than the morula only one pregnancy was achieved, which ended in a spontaneous abortion.
By using blastocyst culture the genetic risk is not avoided, but is much decreased. A significantly higher proportion of genetically abnormal embryos is found among arrested embryos; aneuploidy mosaicism was found in almost 37% of arrested embryos (Ménézo and Ben Khalifa, 1995). In yet another study the percentage of abnormal cells was 54% in arrested embryos, and 17.1% in blastocysts (Veiga et al., 1999
). Our study confirms the finding that after prolonged culture, arrested embryos lead to a spontaneous abortion, therefore the transfer of arrested embryos is not recommended. Moreover, if on day 5 only blastocysts had been transferred, the clinical pregnancy rate per started cycle would have been approximately the same as with the transfer on day 2. In this case, however, many women would have been saved from having a transfer and pregnancy that would end in an abortion. Also, prolonged culture of embryos improves the selection of embryos for cryopreservation thus avoiding the freezing of arrested embryos.
We did not observe any correlation between the female age, female indications of infertility, and the number of blastocysts in the couple. Most cycles were performed for the male factor of infertilityazoospermia.
The only correlation we found was a positive correlation between the serum FSH concentration in the male partner and the number of arrested embryos that did not reach the morula stage on day 5. In men with high serum FSH concentrations (20 IU/l) there was a significantly lower proportion of morulae and a higher proportion of embryos arrested prior to reaching the morula stage. We also found a higher proportion of men with only arrested embryos after ICSI with testicular sperm than in patients with normal serum FSH concentrations. Negative paternal effects were expressed at lower cell stages, whereas the proportion of blastocysts was approximately the same as in patients with normal serum FSH. We consider it very likely that an increased number of arrested embryos in men with high FSH is related to the switch from maternal to embryonic genome at the 48-cell stage (Bolton et al., 1989
).
Serum FSH concentration is not a highly predictive factor for successful testicular sperm recovery in azoospermic patients (Tournaye et al., 1997). No strong predictors for successful testicular sperm recovery are available except histopathology (Tournaye et al., 1997
). FSH concentrations correlate with spermatogenetic activity. However, the prediction of successful sperm retrieval is not absolutely reliable. Testicular sperm extraction can also be successful when FSH hormone concentrations are outside the threshold levels (Bohring et al., 2002
). It is possible to obtain sperm from patients with markedly elevated serum FSH (38.7 IU/l) as reported by Gil-Salom (Gil-Salom et al., 1995
). In our study the highest serum FSH concentration at which testicular sperm were retrieved was 38.3 IU/l. Besides, 61% of men included in our study had increased serum FSH levels (
10 IU/l), and 28% of men had high serum FSH concentration (
20 IU/l). Therefore, the negative effect of high FSH should not be overlooked.
FSH concentrations might reflect the testicular sperm quality. Egozcue showed that meiotic disorders in infertile men are frequent, and increase with high FSH concentrations (Egozcue et al., 2000). These patients produce more sperm with autosomal and sex chromosomal disomies and diploid sperm, originating either from meiotic mutations or from a compromised testicular environment. It has been stated that sperm concentration <1 x 106/ml and/or serum FSH concentration >10 IU/l are the only predictors of male germ cell meiotic abnormalities (Vendrell et al., 1999
).
There is a link between gonadal failure (high serum FSH levels) and the occurrence of sperm chromosome aneuploidies (Levron et al., 2001). Testicular sperm have higher rates of sperm aneuploidy and diploidy than ejaculated sperm (Bernardini et al., 2000
; Mateizel et al., 2002
). Paternal factors negatively affecting the embryo development are related to anomalies of male germ cell DNA condensation (Francavilla et al., 2001
) and fragmentation (Tesarik et al., 2001
; Evenson et al., 2002
), as well as to centrosome anomalies (Hewitson et al., 2002
). The factors leading to azoospermia may affect testicular sperm morphology (Yavetz et al., 2001
).
In our study there was a strong negative correlation between FSH concentrations and Johnsens score. The serum FSH concentrations of 10 IU/l provided a mean Johnsens score of 5, and the FSH concentration of 20 IU/l, a Johnsens score of 2. These elevated FSH concentrations mainly correspond to immature germ cells or absence of germ cells. In most patients with high serum FSH concentration (20 IU/l) we extracted sperm from the sites of focal spermatogenesis; immature germ cells prevailed. FSH level >20 IU/l might represent the threshold level of testicular sperm maturity and explain the arrest of embryo development.
We found no statistical difference in the developmental potential of embryos in patients with obstructive versus non-obstructive azoospermia. Some men with non-obstructive azoospermia had a normal or only slightly elevated serum FSH concentration (i.e. azoospermia with maturation arrest), similar to that in men with obstructive azoospermia. Male serum FSH seems to be one of the most important factors for testicular sperm quality and embryo development.
Blastocyst formation is a good indicator of clinical results after ICSI with testicular sperm in terms of high implantation rate and low abortion rate. High male serum FSH concentrations negatively affect the developmental potential of embryos, these negative paternal effects being manifested before the morula stage.
![]() |
Acknowledgements |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Balaban, B., Urman, B., Isiklar, A., Alatas, C., Mercan, R., Aksoy, S. and Nuhoglu, A. (2001) Blastocyst transfer following intracytoplasmic injection of ejaculated, epididymal or testicular spermatozoa. Hum. Reprod., 16, 125129.
Behr, B., Pool, T.B., Milki, A.A., Moore, D., Gebhardt, J. and Dasig, D. (1999) Preliminary clinical experience with human blastocyst development in vitro without co-culture. Hum. Reprod., 14, 454457.
Bernardini, L., Gianaroli, L., Fortini, D., Conte, N., Magli, C., Cavani, S., Gaggero, G., Tindiglia, C., Ragni, N. and Venturini, P.L. (2000) Frequency of hyper-, hypohaploidy and diploidy in ejaculate, epididymal and testicular germ cells of infertile patients. Hum. Reprod., 15, 21652172.
Bohring, C., Schroeder-Printzen, I., Weidner, W. and Krause, W. (2002) Serum levels of inhibin B and follicle-stimulating hormone predict successful sperm retrieval in men with azoospermia who are undergoing testicular sperm extraction. Fertil. Steril., 78, 11951198.[CrossRef][ISI][Medline]
Bolton, V.N., Hawes, S.M., Taylor, C.T. and Parsons, J.H. (1989) Development of spare human preimplantation embryos in vitro: An analysis of the correlations among gross morphology, cleavage rates, and development to the blastocyst. J. In vitro Fertil. Embryo Transfer, 6, 3035.[ISI][Medline]
Dumoulin, J.M., Coonen, E., Bras, M., Bergers-Janssen, J.M., Ignoul-Vanvuchelen, R.C., van Wissen, L.C., Geraedts, J.P. and Evers, J.L. (2001) Embryo development and chromosomal anomalies after ICSI: effect of the injection procedure. Hum. Reprod., 16, 306312.
Egozcue, S., Blanco, J., Vendrell, J.M., Garcia, F., Veiga, A., Aran, B., Barri, P.N., Vidal, F. and Egozcue, J. (2000) Human male infertility: chromosome anomalies, meiotic disorders, abnormal spermatozoa and recurrent abortion. Hum. Reprod. Update, 6, 93105.
Evenson, D.P., Larson, K.L. and Jost L.K. (2002) Sperm chromatin structure assay: its clinical use for detection of sperm DNA fragmentation in male infertility and comparison with other techniques. J. Androl., 23, 2543.
Francavilla, S., Bianco, M.A., Cordeschi, G., DAbrizio, P., De Stefano, C., Properzi, G. and Francavilla, F. (2001) Ultrastructural analysis of chromatin defects in testicular spermatids in azoospermic men submitted to TESE-ICSI. Hum. Reprod., 16, 14401448.
Gardner, D.K., Schoolcraft, W.B., Wagley, L., Schlenker, T., Stevens, J. and Hesla, J. (1998) A prospective randomized trial of blastocyst culture and transfer in in-vitro fertilization. Hum. Reprod., 13, 34343440.[Abstract]
Gil-Salom, M., Remohi, J., Minguez, Y., Rubio, C. and Pellicer, A. (1995) Pregnancy in an azoospermic patient with markedly elevated serum follicle-stimulating hormone levels. Fertil. Steril., 64, 12181220.[ISI][Medline]
Griffiths, T.A., Murdoch, A.P. and Herbert, M. (2000) Embryonic development in vitro is compromised by the ICSI procedure. Hum. Reprod., 15, 15921596.
Hewitson, L., Simerly, C.R. and Schatten G. (2002) Fate of sperm components during assisted reproduction: implications for infertility. Hum. Fertil. (Camb), 5, 110116.
Holstein, A.F., Schulze, W. and Breucker, H. (1994) Histopathology of human testicular and epididymal tissue. In Hergreave, T.B. (ed), Male Infertility. Springer Verlag, London, pp 105148.
Janny, L. and Ménézo, Y. (1994) Evidence for a strong paternal effect on human preimplantation embryo development and blastocyst formation. Mol. Reprod. Dev., 38, 3642.[ISI][Medline]
Kahraman, S., Kumtepe, Y., Sertyel, S., Donmez, E., Benkhalifa, M., Findikli, N. and Vanderzwalmen, P. (2002) Pronuclear morphology scoring and chromosomal status of embryos in severe male fertility. Hum. Reprod., 17, 31933200.
Karaki, R.Z., Samarraie, S.S., Younis, N.A., Lahloub, T.M. and Ibrahim, M.H. (2002) Blastocyst culture and transfer: a step toward improved in vitro fertilization outcome. Fertil. Steril., 77, 114118.[CrossRef][ISI][Medline]
Langley, M.T., Marek, D.M., Gardner, D.K., Doody, K.M. and Doody, K.J. (2001) Extended embryo culture in human assisted reproduction treatments. Hum. Reprod., 16, 902908.
Levron, J., Aviram-Goldring, A., Madgar, I., Raviv, G., Barkai, G. and Dor, J. (2001) Sperm chromosome abnormalities in men with severe male factor infertility who are undergoing in vitro fertilization with intracytoplasmic sperm injection. Fertil. Steril., 76, 479484.[CrossRef][ISI][Medline]
Mateizel, I., Verheyen, G., Van Assche, E., Tournaye, H., Liebaers, I. and Van Steirteghem, A. (2002) FISH analysis of chromosome X, Y and 18 abnormalities in testicular sperm from azoospermic patients. Hum. Reprod., 17, 22492257.
Ménézo, Y.J. and Ben Khalifa, M. (1995) Cytogenetic and cryobiology of human cocultured embryos: 3-year experience. J. Assist. Reprod. Genet., 12, 3540.[ISI][Medline]
Ménézo, Y., Chouteau, J., Guyader-Joly, C. and Veiga, A. (1999) Sequential media: why and how? Contracept. Fertil. Sex., 27, 449451.[ISI][Medline]
Miller, J.E. and Smith, T.T. (2001) The effect of intracytoplasmic sperm injection and semen parameters on blastocyst development in vitro. Hum. Reprod., 16, 918924.
Obasaju, M., Kadam, A., Sultan, K., Fateh, M. and Munné, S. (1999) Sperm quality may adversely affect the chromosome constitution of embryos that result from intracytoplasmic sperm injection. Fertil. Steril., 72, 11131115.[CrossRef][ISI][Medline]
Palermo, G., Joris, H., Devroey, P. and Van Steirteghem, A.C. (1992) Pregnancies after intracytoplasmic injection of single spermatozoon into an oocyte. Lancet, 340, 1718.[ISI][Medline]
Plachot, M., Belaisch-Allart, J., Mayenga, J.M., Chouraqui, A., Serkine, A.M. and Tesquier, L. (2000) Blastocyst stage transfer: the real benefits compared with early embryo transfer. Hum. Reprod., 15 (Suppl 6), 2430.
Sakkas, D. (1999) The use of blastocyst culture to avoid inheritance of an abnormal paternal genome after ICSI. Hum. Reprod., 14, 45.
Sandalinas, M., Sadowy, S., Alikani, M., Calderon, G., Cohen, J. and Munné, S. (2001) Developmental ability of chromosomally abnormal human embryos to develop to the blastocyst stage. Hum. Reprod., 16, 19541958.
Shoukir, Y., Chardonnens, D., Campana, A, and Sakkas, D. (1998) Blastocyst development from supernumerary embryos after intracytoplasmic sperm injection: a paternal influence? Hum. Reprod., 13, 16321637.[Abstract]
Silber, S.J., Sadowy, S., Lenahan, K., Kilani, Z., Gianaroli, L. and Munné, S. (2002) Chromosomal abnormalities in embryos derived from testicular sperm extraction. Hum. Reprod., 17 (Abstract Bk 1), O-104.
Tesarik, J., Greco, E. and Mendoza, C. (2001) Assisted reproduction with in-vitro-cultured testicular spermatozoa in cases of severe germ cell apoptosis: a pilot study. Hum. Reprod., 16, 26402645.
Tournaye, H., Verheyen, G., Nagy, P., Ubaldi, F., Goossens, A., Silber, S., Steirteghem, A.C. and Devroey, P. (1997) Are there any predictive factors for successful testicular sperm recovery in azoospermic patients? Hum. Reprod., 12, 8086.[CrossRef][ISI][Medline]
Van Steirteghem, A.C., Nagy, Z., Joris, H., Liu, J., Staessen, C., Smitz. J., Wisanto, A. and Devroey, P. (1993) High fertilization and implantation rates after intracytoplasmic sperm injection. Hum. Reprod., 8, 10611066.[Abstract]
Veiga, A., Gil, Y., Boada, M., Carrera, M., Vidal, F., Boiso, I., Ménézo, Y. and Barri P.N. (1999) Confirmation of diagnosis in preimplantation genetic diagnosis (PGD) through blastocyst culture: preliminary experience. Prenat. Diagn., 19, 12421247.[CrossRef][ISI][Medline]
Vendrell, J.M., Garcia, F., Veiga, A., Calderon, G., Egozcue, S., Egozcue, J. and Barri, P.N. (1999) Meiotic abnormalities and spermatogenic parameters in severe oligoasthenozoospermia. Hum. Reprod., 14, 375378.
Vicdan, K., Isik, A.Z. and Delilbasi, L. (2001) Development of blastocyst-stage embryos after round spermatid injection in patients with complete spermiogenesis failure. J. Assist. Reprod. Genet., 12, 319328.
Wilson, M., Hartke, K., Kiehl, M., Rodgers, J., Barabec, C. and Lyles, R. (2002) Integration of blastocyst transfer for all patients. Fertil. Steril., 77, 693696.[CrossRef][ISI][Medline]
Yavetz, H., Yogev, L., Kleiman, S., Botchan, A., Hauser, R., Lessing, J.B. and Gamzu, R. (2001) Morphology of testicular spermatozoa obtained by testicular sperm extraction in obstructive and nonobstructive azoospermic men and its relation to fertilization success in the in vitro fertilization-intracytoplasmic sperm injection system. J. Androl., 22, 376381.
Submitted on November 5, 2002; accepted on January 1, 2003.