Blastocyst development from supernumerary embryos after intracytoplasmic sperm injection: a paternal influence?

The success of intracytoplasmic sperm injection (ICSI) warrants further study on the role of paternal factors in early human embryogenesis. To investigate whether poor sperm parameters can influence embryo development, we examined the development of ICSI-fertilized embryos to the blastocyst stage. We present results of blastocyst development from supernumerary ICSI embryos after co-culture on monkey kidney epithelial cells. In addition, we compare the development of supernumerary embryos to the blastocyst stage after ICSI and in-vitro fertilization (IVF). Of 168 supernumerary ICSI embryos, 45 (26.8%) developed to blastocysts. Sperm concentration and morphology did not influence blastocyst development. In contrast, blastocysts arose from spermatozoa that had a significantly higher (P = 0.015) forward progressive motility compared with spermatozoa from those patients who failed to produce blastocysts (42.7% versus 28.2%, respectively). Overall the rate of embryo development to the blastocyst stage after ICSI was lower (26.8%) than that after IVF (47.3%). When the rate of blastocyst development was calculated for patients with three or more supernumerary embryos, it remained significantly higher for the IVF patients than for the ICSI patients (45.6% versus 30.0%). There was no significant difference in the mean cell number and quality of the supernumerary embryos between the IVF and ICSI patients. This study confirms previous reports that have postulated that abnormal spermatozoa may manifest a negative paternal effect on preimplantation embryo development.      

High fertilization and implantation rates after intracytoplasmic sperm injection

Previously reported better fertilization rate after intra-cytoplasmicsingle sperm injection (ICSI) than after subzonal inseminationof several spermatozoa was confirmed in a controlled comparisonof the two procedures in 11 patients. Intracytoplasmic sperminjection was carried out in 150 consecutive treatment cyclesof 150 infertile couples, who had failed to have fertilizedoocytes after standard in-vitro fertilization (IVF) proceduresor who were not accepted for IVF because not enough motile spermatozoawere present in the ejaculate. A single spermatozoon was injectedinto the ooplasm of 1409 metaphase II oocytes. Only 117 oocytes(8.3%) were damaged by the procedure and 830 oocytes (64.2%of the successfully injected oocytes) had two distinct pronucleithe morning after the injection procedure. The fertilizationrate was not influenced by semen characteristics. After 24 hof further in-vitro culture, 71.2% of these oocytes developedinto embryos, which were transferred or cryopreserved. Only15 patients did not have embryos replaced. Three-quarters ofthe transfers were triple-embryo transfers. High pregnancy rateswere noticed since 67 pregnancies were achieved, of which 53were clinical, i.e. a total and clinical pregnancy rate of 44.7%and 35.3% per started cycle and 49.6% and 39.2% per embryo transfer.A total of 237 supernumerary embryos were cryopreserved in 71treatment cycles.     

Comparison of clinical outcome after cryopreservation of embryos obtained from intracytoplasmic sperm injection and in-vitro fertilization

The impact of intracytoplasmic sperm injection (ICSI) on cryopreservedzygotes and embryos was evaluated by comparing embryo survivaland implantation between embryos derived from ICSI and thosederived from standard insemination procedures. The study includedpatients whose excess zygotes and embryos were cryopreservedbetween September 1993 and December 1994 and who subsequentlyunderwent a frozen embryo transfer. Embryo survival, clinicalpregnancy rates per transfer and pregnancy outcome were compared.Three hundred and thirty eight cryopreservation cycles, duringwhich 1471 embryos were cryopreserved, were included in thisstudy. Of those, 961 were derived from oocytes fertilized byinsemination in vitro and 510 were derived from oocytes fertilizedby ICSI. A total of 690 of the embryos (451 in the inseminationgroup and 239 in the ICSI group) have since undergone a thawcycle. The embryo survival rates were similar between the twogroups (70.5 and 73.2%, insemination and ICSI respectively)and were not significantly affected by the stage at cryopreservation.There was no significant difference in pregnancy rates per transfer(31.8 and 32.3%), the preclinical pregnancy loss rate (16.7and 23.8%), or the clinical miscarriage rate (16.7 and 23.8%)between the insemination and the ICSI groups respectively. Itis concluded that ICSI does not have an adverse impact on thesurvival and successful implantation of cryopreserved and thawedembryos.     

Comparison of in-vitro development of embryos originating from either conventional in-vitro fertilization or intracytoplasmic sperm injection

In this retrospective study on 1628 consecutive cycles performed during a period of 4 years, development in vitro is compared of embryos obtained after either conventional in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). At 39-42 h after insemination or injection, embryos obtained after ICSI were significantly (P < 0.01) further developed (mean cell number 3.48 +/- 0.03) as compared with those obtained after IVF (3.22 +/- 0.03), whereas after 63-66 h of in-vitro development this difference was no longer present (mean cell number 6.11 +/- 0.15 versus 6.09 +/- 0.13 respectively). Culture of surplus embryos obtained after IVF resulted in a significantly higher (P < 0.001) mean incidence of blastocyst formation per cycle as compared with the ICSI group (31.8 +/- 1.9 versus 23.0 +/- 1.4 respectively). Blastocysts from both groups consisted of comparable numbers of cells. Blastocyst formation was also significantly higher when embryos were cultured in groups (31.2 +/- 1.8) compared to single culture (23.1 +/- 1.5; P < 0.01), in human tubal fluid (HTF) medium (29.2 +/- 1.7) compared with IVF-50(TM) medium (24.2 +/- 1.6; P < 0.01), and when they were cultured under 5% O(2) (30.3 +/- 1.5) compared with 20% O(2) (21.7 +/- 1.7; P < 0.01). In all culture conditions used, the mean incidence of blastocyst formation per cycle showed comparable differences in favour of the IVF group as compared with the ICSI group.     

Oocyte morphology does not correlate with fertilization rate and embryo quality after intracytoplasmic sperm injection

The fertilization rates and further development of 528 humanmetaphase IT oocytes directly injected by a single spermatozoonwere analysed with respect to their morphological features atthe light microscopy level at the time of retrieval. The deviationsof oocyte morphology which were most frequently observed, afterremoval of cumulus cells, were dark incorporations, dark zonapellucida, large peri-vitelline space, spots, vacuoles, refractilebodies and irregular shape. These deviations correlated neitherwith the fertilization rate nor with the embryo quality score,as compared to ‘ideal’ oocytes. Since the majorityof oocytes displayed deviations from the ‘ideal’morphotype but were still fertilized and developed in cultureat a normal rate, they were probably as normal as ‘ideal’oocytes. Since some of these morphotypes, such as refractilebodies, have been shown to be associated with failure of fertilization,it seems that intracytoplasmic sperm injection may be an appropriatemethod of treatment for couples in whom repeated failure ofin-vitro fertilization is associated with the retrieval of dysmorphicoocytes in the presence of normal semen characteristics.     

Aetiology of failed and abnormal fertilization after intracytoplasmic sperm injection1

The aim of this study was to determine why oocytes remain unfertilizedor develop three pronuclei after intracytoplasmic sperm injection(ICSI). Unfertilized and abnormally fertilized oocytes werefixed in glutaraldehyde,stained with Hoechst 33342 and examinedby fluorescence microscopy to identify oocyte, sperm and polarbody DNA.One-pronuclear oocytes were considered to be unfertilized.Atotal of 285 unfertilized oocytes were examined (104 ICSI cycles).Overall, 83% of these oocytes were not activated (still at metaphaseII) while 17% had activated and formed a single (female) pronucleus.About 66% of the unfertilized, metaphase II oocytes containeda swollen sperm head, indicating that the oocyte was correctlyinjected but had failed to activate and complete the secondmeiotic division. Premature chromosome condensation of the spermDNA was evident in 6% of these metaphase II oocytes (4% of theunfertilized oocytes). The swollen sperm head was located amongthe oocyte chromosomes in 5%of the metaphase II oocytes. Othercauses of failed fertilization in the metaphase II oocytes werethe failure of sperm head decondensation (11%) and ejectionof the spermatozoon from the oocyte (23%). A similar patternwas observed in one-pronuclear oocytes (52%, swollen sperm head;28%, intact, undecondensed sperm head; 20%, ejection of thespermatozoon), which indicates that asynchronous pronucleardevelopment does not explain the presence of one-pronuclearoocytes. A total of 41 threepronuclear oocytes were examinedand all had a single polar body, which indicates that the retentionof the second polar body leads to the formation of the thirdpronucleus.In conclusion, this study demonstrates that: (i)the major cause of fertilization failure after ICSI is failureof oocyte activation; (ii) ejection of the spermatozoon intothe perivitelline space is not a major cause of fertilizationfailure;and (iii) sperm head decondensation and oocyte activationafter ICSI can occur independently.     

Comparison of pregnancy outcome after intracytoplasmic sperm injection and in-vitro fertilization

The aim of this study was to compare pregnancy characteristics and perinatal outcome of intracytoplasmic sperm injection (ICSI) pregnancies with pregnancies obtained after in-vitro fertilization (IVF). Retrospectively, 145 ICSI pregnancies were matched with 145 IVF pregnancies using the last menstruation data. The main outcome measures were preclinical and clinical abortions, ectopic pregnancies, multiple gestations, prenatal morbidity, prematurity, Caesarean section, birthweight, perinatal mortality and malformations for singletons, twins and triplets. Although patients were significantly younger (P < 0.001) in ICSI (31 years) than in IVF (33 years), their infertility duration (5 years) was similar. The mean number of transferred embryos (2.7 embryos per transfer) was similar in IVF and ICSI. The rates of preclinical (15%) and clinical abortions (11% in ICSI versus 15% in IVF) were not different. Four ectopic pregnancies were observed in the IVF group and none in the ICSI group. In ICSI, two minor malformations were detected and two therapeutic abortions were performed respectively for polymalformations and suspicion of cystic fibrosis. The rate of congenital malformation was 2.8% in ICSI and 2.2% in IVF. In this last group, one therapeutic abortion for malformation of neural tube was performed and two minor malformations were detected. The rate of aborted embryonic sacs before 16 weeks of gestation was not significantly lower in ICSI compared with IVF (13.7% versus 20%). The rate of multiple gestations was similar in both groups (31% in IVF and 35% in ICSI). The number of Caesarean sections was similar in IVF and in ICSI and was twice as frequent for twins versus singletons. The number of singletons born by Caesarean section was 21% after ICSI and 17% after IVF. Mean birthweights and gestational ages at birth for twins were significantly higher (P < 0.05) in ICSI than in IVF (2488 versus 2281 g and 36.5 versus 35.5 weeks). This difference was not observed for singletons. In conclusion, pregnancy characteristics and perinatal outcome after ICSI showed no increase in the number of pathologies in comparison with IVF.      

Endometrial thickness as a predictor of pregnancy after in-vitro fertilization but not after intracytoplasmic sperm injection

An ultrasonographic evaluation of the endometrium was performedin 158 patients undergoing ovarian stimulation for an in-vitroassisted reproduction programme. Endometrial thickness was evaluatedin 109 patients undergoing in-vitro fertilization (IVF) forfemale indications and in 49 patients undergoing intracytoplasmicsperm injection (ICSI) for male indications. The maximal endometrialthickness was measured on the day of human chorionic gonadotrophin(HCG) administration by longitudinal scanning of the uteruson the frozen image using electronic callipers placed at thejunction of the endometrium-myometrium interface at the levelof the fundus. Cases in which the endometrial thickness was10 mm were included in group A; cases in which the endometrialthickness was <10 mm were assigned to group B. The age ofthe patients, serum 17- oestradiol concentrations on the dayof HCG administration, the length of follicular stimulation,the number of follicles, 17- oestradiol concentrations per follicleon the day of HCG and the number of embryos transferred wereanalysed in each case. When comparing endometrial thicknessand results in IVF and ICSI patients, an endometrium <10mm predominated in IVF patients (27.5%) compared with thoseundergoing ICSI (16.7%) (P=0.05); conversely an endometrium10 mm was more frequent in ICSI than in IVF patients. The incidenceof pregnancy was higher in IVF group A patients (32/79; 41%)than in IVF group B patients (5/30; 17%) (P=0.03), whereas nosignificant difference was found between ICSI group A (13/42;31%) and ICSI group B (3/7; 43%) patients. Thus, a higher percentageof IVF patients had thin endometrium when compared with ICSIpatients; thin endometrium was a prognostic indicator of pregnancyonly in the case of a female indication for infertility (IVF).A thin endometrium in cases of female infertility may reflecta previous or present uterine pathology, whereas in indicationsof male infertility (i.e. cases using ICSI), in the absenceof any associated uterine pathology, the presence of a thinendometrium is not predictive.     

Fertiliza1tion and early embryology: Ultrastructural analysis of fertilization failure after intracytoplasmic sperm injection

Human oocytes that failed to display signs of fertilizationby 44 h after intracytoplasmic sperm injection (ICSI) were processedfor electron microscopic analysis. All oocytes were arrestedat metaphase II. The first polar body contained intact corticalgranules and chromosome clumps, which were not surrounded bya nuclear envelope but still associated with microtubules. Whena second globular body was present, it always showed the sameultrastructure, indicating that it had originated from fragmentationof the first polar body and not from the resumption of the secondmeiotic division. The most prominent organelles of the oocytecytoplasm were the smooth endoplasmic reticulum and mitochondria.In the oocyte cortex, cortical granules were intact, with nosigns of incipient or incomplete cortical reaction. Oocyte chromosomeswere found in the oocyte periphery near the locality of thefirst polar body extrusion. They consisted of dense aggregatesof chromatin associated with microtubules. The chromatin ofthe injected spermatozoon was demembranated and partially decondensed.In some cases, vesicular and tubular structures, apparentlyof oocyte origin, were associated with the periphery of thesperm chromatin mass but they never formed a continuous layer.These data suggest that fertilization failure after ICSI isbasically a failure of oocyte activation.     

The chromosomal constitution of embryos developing from abnormally fertilized oocytes after intracytoplasmic sperm injection and conventional in-vitro fertilization

The aim of this study was to analyse the chromosomal constitution of embryos developing from mono- (1PN) and tripronuclear (3PN) oocytes, after in-vitro fertilization (IVF) and after intracytoplasmic sperm injection (ICSI) into oocytes, by means of the fluorescent in-situ hybridization (FISH) technique with specific probes for the chromosomes X, Y and 18. FISH analysis was carried out on embryos from 3PN oocytes: 106 after ICSI and 71 after conventional IVF. In the 3PN embryos after ICSI, equal ratios of XXX and XXY were observed and no XYY embryos were present. This shows the digynic origin of such 3PN embryos. On the other hand, after conventional IVF, the XYY status indicative of dispermic fertilization was observed in some embryos. After IVF, only 12.7% of the 3PN oocytes developed into embryos with uniformly triploid blastomeres, compared with 55.7% after ICSI (P < 0.001). On the other hand, after ICSI only 16.0% of the embryos developing from 3PN oocytes were mosaic, compared with 42.3% after conventional IVF (P < 0.001). FISH was also carried out on embryos from 1PN oocytes: 61 after ICSI and 115 after conventional IVF. In 35.6% of IVF embryos developing from 1PN oocytes Y-specific hybridization signals were observed. This indicates that in 70-75% of such cases a spermatozoon had penetrated the oocyte and that only 25-30% of them were parthenogenetic. A significantly higher proportion (P < 0.001) of embryos developing from 1PN oocytes were diploid after IVF (48.7%) than after ICSI (27.9%); equal ratios of XX and XY embryos were observed in the two groups. Formation of a single pronucleus in an embryo subsequently shown to be diploid indicates that normal fertilization was followed by asynchronous formation of pronuclei. A significantly (P < 0.001) higher proportion of 1PN oocytes developed into haploid embryos after ICSI (31.2%) than after conventional IVF (13.1%). In both groups most of the haploid embryos were X-bearing (IVF, 93.3%; ICSI, 84.2%) and only a few were Y-bearing (IVF, 6.7%; ICSI, 15.8%). A contribution of normal fertilization and androgenetic activation thus led to 1PN oocytes. Gynogenetic and/or parthenogenetic activation, both leading to indistinguishable chromosomal distributions, also contributed to the formation of 1PN oocytes after ICSI and IVF.      

In-vitro fertilization and intracytoplasmic sperm injection in the treatment of infertility after testicular cancer

Treatment of testicular cancer (TC) may cause infertility due to reduced sperm quality with or without an ejaculation problem. In cases of anejaculation or retrograde ejaculation, spermatozoa can be obtained by transrectal electroejaculation (TE) or testicular sperm extraction (TESE) and used for in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). In this study, 15 out of 17 couples evaluated for infertility after TC, underwent a total of 21 treatment cycles, resulting in 18 embryo transfers. Spermatozoa were obtained by TE in 16 cycles, by masturbation in three cycles and by TESE in one. In one cycle no spermatozoa were found using TESE. Fertilization and cleavage was achieved by IVF in seven cycles and ICSI in 11 cycles; average fertilization rates of 57 and 55% respectively were observed. Twelve clinical pregnancies occurred, of which 11 have been delivered or are ongoing. The ongoing pregnancy rate was 57% per cycle. These results show that infertility after testicular cancer can be treated effectively with IVF and that ICSI even permits treatment of patients who have severe oligozoospermia.      

Oocyte morphology does not affect fertilization rate, embryo quality and implantation rate after intracytoplasmic sperm injection

In this study, we compared the fertilization rate and embryo quality after intracytoplasmic sperm injection (ICSI) as they relate to oocyte morphology. A total of 654 ICSI cycles yielding 5903 metaphase II oocytes were observed. The oocytes retrieved in these cycles were divided into (i) normal oocytes, (ii) oocytes with extracytoplasmic abnormalities (dark zona pellucida and large perivitelline space), (iii) oocytes with cytoplasmic abnormalities (dark cytoplasm, granular cytoplasm, and refractile body), (iv) oocytes with shape abnormalities, and (v) oocytes with more than one abnormality (double and triple abnormalities). Intracytoplasmic vacuoles and aggregates of smooth endoplasmic reticulum were not recorded separately. The fertilization rate and quality of morphologically graded embryos did not differ between the groups. There were 77 cycles where all transferred embryos were derived from abnormal oocytes, and 164 cycles where all embryos were derived from normal oocytes. These cycles were studied further. The two groups were comparable regarding mean female age, duration of infertility, duration of ovarian stimulation, number of ampoules of gonadotrophin injected, and number of oocytes retrieved. Two clinical pregnancy rates (44.4 versus 42.1%) and implantation rates per embryo (10.3 versus 13.2%) were similar. In conclusion, in couples undergoing ICSI, abnormal oocyte morphology is not associated with a decreased fertilization rate or unfavourable embryo quality. Furthermore, embryos derived from abnormal oocytes yield similar clinical pregnancy and implantation rates when transferred compared with embryos derived from normal oocytes.      

The influence of the site of sperm deposition and mode of oolemma breakage at intracytoplasmic sperm injection on fertilization and embryo development rates

The aims of this study were to examine, in a prospective, controlledway, the effect of the sperm deposition site in the oocyte andthe mode of oolemma breakage in intracytoplasmic sperm injection(ICSI) on fertilization and embryo development rates. In thefirst trial (100 cyclesin total), the spermatozoa were depositedfurther from themeiotic spindle (polar body at the 12 o'clockposition) in half of the oocytes (n = 649), while in the otherhalf(n = 605) the spermatozoa were deposited nearer to themeioticspindle (polar body at the 6 o'clock position). In the secondtrial (6860 oocytes in 624 cycles), five different modes ofmembrane breakage (the reaction of the oolemmato the penetratinginjection needle) at the moment of injection were noted: oolemmabreakage, type A pricking once, no suction (n = 1401); typeB, pricking once, smallsuction (n = 2761); type C, prickingonce, long suctionin = 2310); type D, pricking twice or more,no or small amount of suction (n = 259); and type E, prickingtwiceor more, long suction (n = 129). No differences were observedbetween the 12 and 6 o'clock positions in the survival rate(90 and 90% respectively) and in the normal fertilization rates(78 and 77% respectively). Significantly more transfer qualityembryos (50% fragmentation) were obtained in the 6 o'clock positiongroup (83%) than in the 12 o'clock position group (79%). Inthe second trial, significantly lower survival rates were notedafter membrane breakage type A (82%) than after breakages oftypes B, C, D and E (93, 92, 88 and 88% respectively). Therewere no significant differences present in the normal fertilizationrates (70, 72, 70, 71 and 73% for types A-E respectively), butsignificantly more freeze quality embryos (20% fragmentation)were obtained after injection B (65%) than after injection typesA, C, D and E (59, 61, 55 and 51%respectively). In conclusion,the site of sperm deposition inthe oocyte does not influencethe normal fertilization rate but does affect the embryo developmentrate. Furthermore, the mode of membrane breakage does not influencethe normal fertilization rate but does affect oocyte survivalandembryo development rates.     

Obstetric outcome of pregnancies after the transfer of cryopreserved and fresh embryos obtained by conventional in-vitro fertilization and intracytoplasmic sperm injection.

This study reports the obstetric outcome of pregnancies obtained after the transfer of cryopreserved or fresh embryos where the initial procedure was standard in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Pregnancies obtained after frozen IVF (n = 245) or frozen ICSI (n = 177) were compared with a control group of pregnancies after fresh embryo transfer in standard IVF (n = 245) and ICSI (n = 177) cycles were selected as controls. The controls were matched according to maternal age, parity and date of embryo transfer. In the standard IVF group, the biochemical pregnancy rates in the cryopreserved and fresh groups were 18.8 and 9.8% respectively (P < 0.01). In the ICSI group, the biochemical pregnancy rates in the cryopreserved and fresh groups were 16.4 and 6.8% respectively (P < 0.01). The miscarriage rates were comparable between the cryopreserved and fresh groups. However, in the frozen ICSI group the miscarriage rate (26.0%) was significantly higher than in the frozen conventional IVF group (13.1%) (P = 0.001). The frequencies of preterm deliveries, infants with very low birthweight and intrauterine deaths were similar in the groups. The low birthweight rates in the frozen IVF (16.1%) and ICSI (12.1%) groups were significantly lower than those in the fresh IVF (32.2%) and ICSI (32.7%) groups (P < 0.001). The major malformation rates in the frozen IVF (2.4%) and ICSI (2.9%) groups were not different from the major malformation rates in the fresh IVF (4.5%) and ICSI (2.4%) groups. In conclusion, the cryopreservation process had no negative impact on the outcome of pregnancies over 20 weeks of gestation. Long-term follow-up studies are needed in order to prove the safety of the freezing-thawing process.     

Fertilization and early embryology: Premature chromosome condensation of the sperm nucleus after intracytoplasmic sperm injection

A cytogenetic-cytological study was performed on unfertilizedhuman oocytes (first polar body visible) after intracytoplasmicsperm injection (ICSI) with respect to the rate of prematurelycondensed sperm chromosomes (G₁-PCC). Out of 163 prepared oocytesderived from 41 ICSI cycles, 133 (-82%) could be analysed successfully.A total of 60 oocytes (45.1%) showed metaphase II chromosomesin the haploid range along with an intact sperm head and 27oocytes (20.3%) were missing the sperm head, but two of themshowed an approximately diploid set of chromosomes; 38 oocytes(28.6%) exhibited the maternal metaphase II chromosomes as wellas G₁-PCC of the sperm nucleus showing a remarkable variationin the degree of condensation. Ten ICSI cycles (each followedby an embryo transfer) were characterized each by 2–3oocytes demonstrating G₁-PCC. It is concluded that the maincause of failed fertilization after ICSI is the failure of oocyteactivation. When the sperm nucleus is able to act with the chromosomecondensing factors and the oocyte does not become activated,this will lead to the induction of PCC. Absence of the spermhead might be due to injection or ejection of the spermatozoonin the perivitelline space except for two cases in which fertilizationmight have occurred. Finally, the observation of both a singlechromatin region (n = 6) or two chromatin regions (n = 2) indicatedoocyte activation which, however, was followed by developmentalarrest.     

Preincubation of human oocytes may improve fertilization and embryo quality after intracytoplasmic sperm injection

The aim of this study was to examine the relationship between different preincubation periods of oocytes and the outcome of intracytoplasmic sperm injection (ICSI). We analysed retrospectively 95 ICSI treatment cycles performed to alleviate severe male-factor infertility. Oocyte collection was performed approximately 36 h after human chorionic gonadotrophin administration. The cumulus-corona-oocyte complexes obtained were incubated until the moment of ICSI. Fertilization, embryo development and implantation rates were analysed in four groups, which were divided according to the time lapse between oocyte retrieval and ICSI: group I, < or =3 h (18 cycles); group II, >3-< or =6 h (52 cycles); group III, >6-< or =9 h (14 cycles); and group IV, >9-< or =12 h (11 cycles). Immediately before ICSI the cumulus and corona cells were removed from the oocytes. A total of 723 metaphase II oocytes were injected: 126 from group I, 380 from group II, 126 from group III and 91 from group IV. The fertilization rates obtained were 52.3, 66.8, 65.1 and 69.2% respectively [P < 0.05 (using the chi2 test) between group I and groups II, III and IV]. Cleavage rates were similar in all groups (68.1, 69.7, 79.2 and 79.3% respectively), but the proportion of good quality embryos (< or =20% fragmentation) was significantly lower (P < 0.05) in group I (24.2%) compared with groups II (39.8%) and IV (39.6%). However, no statistically significant differences were observed between the four groups with regard to implantation rates (11.7, 13.2, 10.4 and 20.4% respectively). The results suggest that a preincubation period between oocyte retrieval and ICSI can improve the fertilization rate and embryo quality. This period might be necessary for some oocytes to reach full cytoplasmic maturity, leading to a higher activation rate upon microinjection.      

Fertilization and embryo development to blastocysts after intracytoplasmic sperm injection in the rhesus monkey

Notwithstanding the thousands of seemingly healthy children born after intracytoplasmic sperm injection (ICSI), it is not yet possible to conclude absolutely that the ICSI procedure might induce some altered development or that the ICSI protocol might not be improved even further. To address this in a clinically relevant system, the developmental potential of rhesus monkey embryos produced by ICSI is reported. Oocytes collected by laparoscopy from gonadotrophin- stimulated fertile females were fertilized by ICSI using spermatozoa obtained from fertile males by electro-ejaculation. Neither sperm immobilization prior to injection nor an additional chemical stimulus were necessary to achieve oocyte activation and pronuclear formation. Survival and activation of the injected oocytes were judged by the extrusion of the second polar body. Successful fertilization was confirmed by the presence of two pronuclei within 12 h post-ICSI. Some oocytes were fixed and processed for the detection of microtubules and chromatin. Fluorescent labelling revealed that by 12 h post-ICSI the male and female pronuclei were closely apposed and eccentrically positioned within a large microtubule aster. ICSI resulted in a 76.6 +/- 14.9% fertilization rate. First cleavage was completed within 24 h post- ICSI. Two-cell ICSI embryos were co-cultured in CMRL medium on a buffalo rat liver cell monolayer until the hatched blastocyst stage. Oocytes collected laparoscopically from stimulated monkeys can be fertilized by ICSI and will complete preimplantation embryo development in vitro demonstrating that the rhesus monkey is an excellent preclinical model for examining and understanding many aspects of human ICSI.