Intracytoplasmic Sperm Injection Group Research Articles

A prospective randomized controlled study of the effect of short coincubation of gametes during insemination on zona pellucida thickness

A prospective, randomized study was conducted to evaluate the thickness of zona pellucida (ZP) after brief or standard exposure of human oocytes to spermatozoa, and to determine the correlation between ZP thickness, fertilization rate and embryo quality. The mean ZP thickness 48 h after insemination was found to be significantly less in fertilized oocytes than in non-fertilized oocytes in all treated groups (13.72 ± 3.0 µm and 15.08 ± 2.5 µm, respectively; p < 0.007). Zona pellucida thickness correlated positively with embryo quality. Brief exposure of gametes was found to influence ZP thickness. The ZP was significantly thinner after brief and intracytoplasmic sperm injection (ICSI) exposure of oocytes to spermatozoa than after standard in vitro fertilization (IVF). The mean ZP thickness 24 and 48 h after fertilization was significantly greater in standard IVF (16.43 ± 2.8 µm and 15.22 ± 2.7 µm, respectively) than in either the brief exposure or ICSI groups (12.78 ± 2.4 µm and 13.01 ± 3.5 µm vs. 13.46 ± 2.2 µm and 13.16 ± 2.4 µm; p < 0.0001).

The Risk of Major Birth Defects After Intracytoplasmic Sperm Injection and in Vitro Fertilization

Although most studies have failed to demonstrate an elevated risk of major birth defects in children conceived by intracytoplasmic sperm injection (ICSI) or standard in vitro fertilization (IVF), most past work is methodologically problematic and definitions of major defects may differ from those applied to naturally conceived infants. This study examined the prevalence of major birth defects diagnosed within 12 months after birth in infants conceived either naturally or using ICSI or IVF. All births took place in Western Australia in the years 1993 to 1997. Data from a reproductive technology registry identified all pregnancies of at least 20 weeks' gestation. The study population included 301 infants conceived by ICSI; 837 conceived by standard IVF; and 4000 conceived naturally. Infants conceived with assisted methods were likelier than those conceived naturally to be delivered by cesarean section, to be born before term, and to have low birth weight. Major birth defects were identified by age 1 year in 8.6% of infants conceived with ICSI, 9.0% of the IVF group, and 4.2% of naturally conceived infants. In all, infants conceived using assisted reproductive technology were more than twice as likely as those conceived naturally to have a major defect. The difference remained significant when only singleton infants, or only singletons born at term, were analyzed, and after adjusting for maternal age and parity and infant gender. Approximately two thirds of major defects were diagnosed in the first week of life, and more than 90% by age 6 months. Excluding defects that may have been diagnosed early because of close surveillance, the odds ratio for a major defect was 1.8 in the ICSI group and 2.2 in the IVF group. Major defects remained about twice as frequent in these groups as with natural conception after excluding infants known to have inherited conditions and those with metabolic disorders. Musculoskeletal and chromosomal defects were significantly more prevalent with assisted reproductive technology. The IVF group (but not ICSI infants) had significantly more cardiovascular, urogenital, and other defects. Multiple major defects were significantly more frequent in the IVF and ICSI groups. Minor birth defects were diagnosed by age 12 months in less than 1% of all groups. These findings support the possibility of an excessive risk of major birth defects in infants born with the benefit of assisted reproductive technology. Nevertheless caution is in order when establishing associations with particular birth defects.

Chromosome analysis of spontaneous abortions after in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI)

Objective: To verify the hypothesis that the incidence of chromosomal abnormalities significantly increases in the products of conception of males with sub-fertility, treated with assisted reproduction techniques (ART). Study design: All removed products of conception tissues were analyzed with standard cytogenetic techniques. A karyotype of the abortions was possible in 35 cases of IVF and 29 of ICSI. Results: 15/35 (43%) IVF abortions and 14/29 (48%) ICSI abortions, respectively, have shown a chromosomal abnormality. The most frequent abnormality was monosomy X (45,X0). Conclusion: No significant difference in the incidence of embryonic anomalies was found between IVF and ICSI group. However, both IVF and ICSI allow pre-implantation diagnosis and embryo chromosomal evaluation should be considered, before transfer. Genetic counselling and consideration of prenatal diagnosis is suggested as integral part of planning of treatment strategies for ‘at risk couples’.

DNA spatial distribution in unfertilized human oocytes by confocal laser scanning microscope.

The aim of this study is to investigate the DNA spatial distribution in unfertilized human oocytes by confocal laser scanning microscope (CLSM). One hundred and forty unfertilized oocytes after conventional in vitro fertilization (IVF) and one hundred and three after intracytoplasmic sperm injection (ICSI) were studied. The chromatin was stained with chromomycin A3 (CA3) initially and at a second step with propidium iodide, allowing the observation of the deprotaminated sperm heads in the ooplasm. CLSM offered the opportunity for studying the three-dimensional position of the spermatozoon in the oocyte and the description of the status of the maternal and paternal chromatin. For each of the IVF and ICSI group of unfertilized oocytes, subgroups were performed according to the status of the maternal and paternal chromatin. The maternal chromosomes were either aligned at metaphase II or disarrayed at metaphase II, and the sperm head was either condensed or swollen/decondensed. Few oocytes were activated and formed a pronucleus. The spatial approaching between paternal and maternal chromatin was calculated for all subgroups of unfertilized oocytes and the distances were compared among them. There was no statistical difference in the distance between the spermatozoon and the maternal chromatin among subgroups of the IVF group, while statistical differences occurred among subgroups of the ICSI group. The spermatozoa in the IVF group approached maternal chromatin more than those in the ICSI group. Movement of the spermatozoon into the oocyte and chromatin remodeling for the formation of pronucleus seem to occur independently and are possibly directed by different mechanisms.

Increase in the monozygotic twinning rate after intracytoplasmic sperm injection and blastocyst stage embryo transfer

Increase in the monozygotic twinning rate after intracytoplasmic sperm injection and blastocyst stage embryo transfer

First-trimester screening for trisomy 21 in singleton pregnancies achieved by assisted reproduction.

The possible effect of assisted reproduction on first-trimester screening for trisomy 21 was examined by fetal nuchal translucency thickness (NT), maternal serum free beta-human chorionic gonadotrophin (HCG) and pregnancy-associated plasma protein-A (PAPP-A). Parameters were measured at 11-14 weeks in 411 singleton pregnancies achieved by controlled ovarian stimulation, including 220 that had undergone IVF. Results were compared with 1233 singleton pregnancies conceived spontaneously. In the IVF pregnancies, the median fetal NT was not significantly different from that in controls, whilst the median free beta-HCG was significantly increased, and PAPP-A was significantly decreased. In the intracytoplasmic sperm injection group, fetal NT and free beta-HCG values were not significantly different from those in controls, but PAPP-A was significantly decreased. In those pregnancies achieved by ovarian stimulation, neither fetal NT, free beta-HCG nor PAPP-A were significantly different from the control group. In IVF pregnancies, screening for trisomy 21 by fetal NT, maternal serum free beta-HCG and PAPP-A levels may be associated with a 1.2% higher false-positive rate than in natural conception.

Conventional in-vitro fertilisation versus intracytoplasmic sperm injection for the treatment of non-male-factor infertility: a randomised controlled trial

Intracytoplasmic sperm injection (ICSI) is a more invasive option than conventional in-vitro fertilisation (IVF), which can be successful even when semen characteristics are poor. Reports of higher fertilisation rates after ICSI suggest that this technique may be better than the conventional method for all couples seeking IVF. We undertook a multicentre randomised controlled trial comparing clinical outcome after ICSI or traditional IVF in couples with non-male-factor infertility. 415 eligible and consenting couples at four UK centres were randomly assigned IVF or ICSI (total 435 treatment cycles: IVF 224; ICSI 211). Usual clinical and laboratory protocols for the two treatment procedures were followed in each of four participating centres. The primary outcome was the implantation rate (number of gestation sacs per embryo replaced expressed as a percentage). Secondary outcomes were pregnancy and fertilisation rates associated with each treatment. Analyses were by intention to treat. The implantation rate was higher in the IVF group than in the ICSI group (95/318 [30%] vs 72/325 [22%]; relative risk 1.35 [95% CI 1.04-1.76]). The pregnancy rate per cycle was also higher after IVF (72 [33%] vs 53 [26%]; 1.17 [0.97-1.35]). Mean associated laboratory time was significantly shorter with IVF than with ICSI (22.9 [SD 12.1] vs 74.0 [38.1] min; 95% CI for difference 45.6-56.6). ICSI offers no advantage over IVF in terms of clinical outcome in cases of non-male-factor infertility. Our results support the current practice of reserving ICSI only for severe male-factor problems.

Outcome in the second year of life after in-vitro fertilisation by intracytoplasmic sperm injection: a UK case-control study

There have been reports suggesting that children born after in-vitro fertilisation by intracytoplasmic sperm injection (ICSI) are at increased risk of neurodevelopmental delay. We have undertaken a case-control study of this issue. We studied 208 singleton children conceived by ICSI and a control group of 221 normally conceived singleton children. Children were recruited from 22 fertility centres and local nurseries throughout the UK. Controls were selected to match cases as closely as possible for social class, maternal educational attainment, region, sex, and race. The primary outcome measure was neurodevelopmental scoring; secondary measures were perinatal outcomes, postnatal health, and congenital abnormalities. A single examiner assessed all the children. A follow-up rate of 90% for the ICSI group was achieved at a mean age of 17 months. No difference between the study children and controls was found in mean neurodevelopmental scores (98.08 [SD 10.93] vs 98.69 [9.99]) or any subscales on the Griffiths' scales of mental development. Perinatal outcome was similar apart from a higher rate of caesarean section (73 [35.1%] vs 53 [24.0%], p=0.015) and a lower mean birthweight (3163 [SD 642] vs 3341 [606] g, p=0.013) in the study group. Rates of major congenital abnormality were also similar overall (ten [4.8%] study vs ten [4.5%] control), although there were significantly more congenital anomalies among children born to fathers with oligozoospermia than in other children. This population study did not show any significant difference between children conceived after ICSI and their naturally conceived peers in terms of physical health and development.

Results of In Vitro Fertilization (IVF) and Intracytoplasmic Sperm Injection (ICSI) with Single Oocyte in Unstimulated Cycles

Results of In Vitro Fertilization (IVF) and Intracytoplasmic Sperm Injection (ICSI) with Single Oocyte in Unstimulated Cycles

A Prospective Randomized Trial of ICSI Versus IVF for the Treatment of Unexplained Infertility

Objectives: It has been reported that fertilization failure is common in patients with unexplained infertility undergoing conventional in-vitro fertilization (IVF). In this study we compared fertilization rates with IVF or intracytoplasmic sperm injection (ICSI) in sibling oocytes of patients with unexplained infertility. Design: Prospective randomized study. Materials and Methods: A total of 85 patients with unexplained infertility were evaluated. We included couples with normal semen parameters (ie. count, motility and morphology) and with at least 8 oocytes retrieved. Oocytes were randomly divided into two groups; conventional IVF was performed in group I while intracytoplasmic sperm injection (ICSI) was performed in group II. Results: A total of 1458 oocytes were retrieved (mean: 17.1), IVF was performed on 726 and ICSI on 722 of them. In both groups G1 and G2 media were used for incubation of the embryos. All embryo transfer procedures were performed 3 days after oocyte retrieval. As shown in table I fertilization rates were 36.6% and 83.3% in group I and II, respectively (p<0.05). Total fertilization failure was observed in sibling oocytes of 11 couples in group I, while all these couples had embryos available for transfer from their oocytes fertilized with ICSI. Cleavage rate and embryo quality were similar between the groups. Embryo quality in 5–8 cell embryos was significantly better in ICSI group. Tabled 1IVFICSIPNo of oocytes726722No of MII oocytes540 (74.8%)Fertilization rate36.5%83.3%<0.05Cleavage rate94.5%97.8%NSDevelopmental stageG1+G2G3+G4G1+G2G3+G4≤2 cell5.6%4.0%3.7%2.6%NSNS2–4 cell19.2%13.6%22.9%22.9%NS<0.055–8 cell26.0%31.6%40.7%25.2%<0.05NS Open table in a new tab Conclusion: Our results show that fertilization rate is significantly higher when oocytes from patients with unexplained infertility are fertilized with ICSI. Serious consideration should be given to ICSI as the first option for in vitro fertilization in these patients.

Poor outcome with round spermatid injection in azoospermic patients with maturation arrest

Objective: To compare the outcome of intracytoplasmic sperm injection (ICSI) and round spermatid injection (ROSI), both obtained by testicular sperm extraction (TESE), and to compare the results of fresh versus frozen ROSI. Design: Retrospective study. Setting: An IVF unit at a university hospital Patient(s): Eighteen infertile couples with nonobstructive azoospermia. Intervention(s): TESE with ROSI or ICSI of mature spermatozoa into metaphase II oocytes was performed. The resulting embryos were transferred to female partners. The spare round spermatids were frozen. Main Outcome Measure(s): Fertilization and cleavage rates, embryo quality, and clinical pregnancy rates. Result(s): Seventeen ROSI cycles and six ICSI cycles were compared. Fertilization rate following ROSI (44.9%) was significantly lower than with ICSI (69%). A significantly higher rate of cleavage arrest occurred following ROSI (40.8%) as compared to ICSI (8.2%). The morphology of embryos resulting from ROSI was significantly poorer. No pregnancies were achieved following ROSI as compared to a 50% clinical pregnancy rate in the ICSI group. The fertilization and cleavage rates following ROSI with fresh versus frozen-thawed spermatids were comparable. Conclusion(s): In azoospermic patients with maturation arrest at the stage of round spermatids the efficiency of ROSI appears to be extremely poor. The role of ROSI in the treatment of nonobstructive azoospermia should be reevaluated.

Comparison between day-2 embryos obtained either from ICSI or resulting from short insemination IVF: influence of maternal age

Short incubation time prevents deleterious effects of cumulus cell degeneration and excess spermatozoa in IVF embryos. We performed a short incubation (3 h) protocol in 328 IVF cycles, in order to compare the developmental potential of regular IVF embryos with those originating from 316 cycles entered our intracytoplasmic sperm injection (ICSI) programme over the same period. Embryo transfers were performed in all patients on day 2. The mean number of embryos transferred was 1.92 for the ICSI group and 1.73 for the IVF group (P < 0.007). This was related only to the wishes of patients. However, the policy of the centre is to transfer a low number of embryos in young patients in order to avoid multiple pregnancies. All spare embryos were permitted to grow to the blastocyst stage for freezing. Shortening incubation time did not decrease fertilization rates. In our overall population, no difference was observed in the implantation rates per embryo for IVF (19%) or for ICSI (20%). An age-related decrease in embryo production was observed for both groups of patients (P < 0.01 for ICSI and P < 0.001 for IVF). The age-related decrease in embryo implantation was only significant for the IVF group (P < 0.03 for patients <30 and >35 years of age). A significant overall decrease in blastocyst formation was observed for spare embryos after ICSI versus IVF (34.2 versus 43.8%; P < 0. 05). The significance of this observation is discussed.

Does ICSI affect early serum beta-HCG in pregnancies achieved after IVF?

This study was conducted to compare early serum human chorionic gonadotrophin (HCG) concentrations in singleton pregnancies achieved after intracytoplasmic sperm injection (ICSI), with those achieved after conventional in-vitro fertilization (IVF). Early serum HCG, 14-16 days after embryo transfer, was analysed in 99 IVF pregnancies achieved after ICSI (group A), and compared to 105 conventional IVF pregnancies (group B). All women were treated at the IVF Unit, Lis Maternity Hospital. Records were studied retrospectively. The mean +/- SE serum HCG concentration on day 14 after embryo transfer in group A was 190.5 +/- 17.4 mIU/ml, compared to 195.7 +/- 14.03 mIU/ml in group B. HCG concentration 14 days after embryo transfer in both groups A and B was higher in women with mechanical factor than in couples with male factor infertility or unexplained infertility (246 +/- 31.4, 183.3 +/- 16.4, 177.98 +/- 14.3 mIU/ml respectively). On the 16th day after embryo transfer, the HCG concentration increased, and the difference between the groups was maintained. Only in the subgroup of unexplained infertility did we find a difference in concentrations of HCG between ICSI and conventional IVF: on the 16th day following embryo transfer in this group there was a significant difference in HCG concentrations (395. 8 +/- 21 and 545.6 +/- 45.7 respectively; P = 0.04). HCG concentrations did not differ overall in the conventional IVF pregnancies compared with those achieved by ICSI. However, a statistical difference in early serum HCG concentrations was found in relation to the aetiology of infertility.

Late fertilization of unfertilized human oocytes in in vitro fertilization and intracytoplasmic sperm injection cycles: conventional insemination versus ICSI.

The aim of this study was to evaluate the efficacy of intracytoplasmic sperm injection (ICSI) in comparison with conventional reinsemination using fertilization failed oocytes by conventional in vitro fertilization (IVF). Oocytes were collected from patients of IVF or ICSI cycles. Patients were grouped by fertilization techniques: group 1: conventional IVF; group 2: reinsemination after conventional IVF failure; group 3: regular ICSI; group 4: 1-day-old ICSI after conventional IVF failure; group 5: 2-day-old ICSI after conventional IVF failure; group 6: re-ICSI after regular ICSI failure. In different insemination groups, normal fertilization rate was higher (P < 0.001) in 1-day-old ICSI (47.1%) and 2-day-old ICSI groups (40.0%) than in reinsemination (14.7%). Abnormal fertilization rate was higher (P < 0.05) in re-ICSI group (21.7%) than any other groups (range: 0-8%). Cleavage rate was higher in 1-day-old (36.7%) and 2-day-old ICSI groups (36.0%) than in reinsemination (5.3%, P < 0.001) or re-ICSI groups (17.4%, P < 0.05). Pregnancy rate was 27.6% and 20.0% in conventional IVF and regular ICSI groups, respectively. However, 1-day-old ICSI (group 4) and 2-day-old ICSI (group 5) were attempted once embryo transfer (ET) but failed pregnancy occurred in each group. In fertilization failure cycles, late ICSI increases the rate of fertilization and embryonic development and may rescue the completely failed attempt of pregnancy.

Comparison of Blastulation and Pregnancy Rates of Fertilized Human Oocytes Obtained after Conventional In Vitro Fertilization and Intracytoplasmic Sperm Injection.

A comparison was made of good quality blastocysts obtained after either conventional in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). After IVF or ICSI, fertilized oocytes were kept in culture for a further 5 to 7 days before embryo transfer (ET) or embryo freezing. No differences were found in the number of oocytes showing two-pronuclei between conventional IVF (76.9%) and ICSI groups (85.1%). A cohort of 60 and 74 oocytes in the pronuclear stage were cultured after IVF and ICSI, respectively. The number of fertilized oocytes reaching the blastocyst stage was significantly higher (P<0.05) in the IVF group (73.3%) than in the ICSI group (56.8%). A total of 86 blastocysts were categorized into three grades depending on their morphology. The number of blastocyst embryos achieving blastocyst grade 1 (BG1) was significantly higher (P<0.05) in the IVF group than in the ICSI group, 63.3% and 13.5%, respectively. In the IVF group, 10.0% and 0% of 2PN oocytes developed to BG2 and BG3, and 2.7% and 4.1% in the ICSI group, respectively, with no significant differences between the two groups. Pregnancy rate was higher in the IVF group than in the ICSI group, 50% and 20%, respectively. It was concluded that fertilized oocytes resulting from ICSI cannnot be successfully cultured for 5-7 days for blastulation and blastocyst-ET.

Effects of electric stimulation on bovine oocyte activation and embryo development in intracytoplasmic sperm injection procedure.

This study was carried out to investigate the efficacy of electric stimulation before and/or after intracytoplasmic sperm injection (ICSI) on bovine oocyte activation and embryo development. The oocytes were treated with electric shock before (B), before and after (B&A), and after (A) sperm injection. In each group, sham ICSI (ICSI-s) was performed to exclude the effect of parthenogenesis (B ICSI-s, B&A ICSI-s, and A ICSI-s). An electric pulse was applied with a single direct current (DC) pulse (0.8 kV/cm, 70 microseconds). One pronucleus (PN) formation in the B&A ICSI-s group was slightly higher than that found in B and B&A ICSI group; however, the difference was not significant. Two PN formation in B&A ICSI group was higher than that found in sham ICSI groups (P < 0.05). There were no differences among treatment groups in the cleavage rate; however, morulae and blastocyst formation in the B&A embryos was significantly higher than that of other groups (P < 0.05) and got pregnant. Electric stimulation before and after injection was an effective method in inducing bovine oocyte activation and in sustaining embryo development to the morulae and blastocyst stage.

Pregnancy potential of embryos from in vitro fertilization compared to intracytoplasmic sperm injection

The aim of this study was to investigate whether equally high-quality embryos derived from standard in vitro fertilization (IVF) or from intracytoplasmic sperm injection (ICSI) differ in pregnancy potential. We evaluated all consecutive cycles from fanuary 1996 to December 1997, in which only high-quality embryos were transferred. A total of 171 IVF and 148 ICSI cycle procedures, conducted in 153 and 130 women respectively, met with the inclusion criteria. A higher clinical pregnancy rate was recorded for the IVF group than the ICSI group (35% versus 29% respectively), although the difference did not achieve statistical significance. This result was detected despite the significantly higher mean age of the IVF patients compared with the ICSI patients (35 ± 4.9 years and 33 ± 5.2 years respectively). Controllingfor the effect of patient age using linear regression analysis yielded a significantly higher clinical pregnancy rate for IVF therapy.In conclusion, IVF is associated with a significantly higher clinical pregnancy rate than ICSI even when high-quality, morphologically comparable embryos are utilized.

Outcome of pregnancies derived from assisted reproductive technologies: IVF versus ICSI.

To compare the course and outcome of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) pregnancies. A retrospective study was conducted in a university-affiliated IVF unit with 200 patients who conceived in 1996-1997, 100 with ICSI and 100 with IVF. Data were retrieved from our prospectively created computerized database. In addition, all patients were interviewed by telephone, and the interviewing physician completed a detailed questionnaire. Findings for the IVF and ICSI pregnancies were compared. The main outcome measures were maternal age, implantation rate, early pregnancy complications, clinical abortion rate, multiple pregnancy delivery rate, gestational age at delivery, mode of delivery, and birth weight. In all, 238 children were born, including 104 singleton infants (45 IVF, 59 ICSI), 49 twin pairs (28 IVF, 21 ICSI), and 12 triplet sets (3 IVF, 9 ICSI). Statistically significant differences between the ICSI and IVF groups were noted for maternal age (31.3 +/- 4.4 vs. 33.4 +/- 4.8, respectively, P < 0.005) and clinical abortion rate (11% vs. 24%, respectively, P < 0.05). ICSI pregnancies in our series were characterized by a lower clinical abortion rate than IVF pregnancies, probably because of the mean younger age of the ICSI group.

A comparison of post-thaw results between cryopreserved embryos derived from intracytoplasmic sperm injection and those from conventional IVF

Objective: To study the effect of freezing on early stage embryos derived from intracytoplasmic sperm injection (ICSI) or from IVF. Design: Prospective, controlled clinical study. Setting: Private IVF center. Patient(s): Sixty-seven consecutive patients undergoing frozen-thawed embryo transfer cycles. Intervention(s): Early stage embryos were frozen, thawed, and transferred. Main Outcome Measure(s): Post-thaw survival, implantation and pregnancy rates. Result(s): We noted an 88% post-thaw survival rate, an 18% implantation rate, and a 52% pregnancy rate in the ICSI group and 81%, 11%, and 25%, respectively, with conventional fertilization. Conclusion(s): Early stage embryos (either zygote or 2–4 cells) derived from ICSI can be frozen with confidence and higher post-thaw survival and pregnancy rates can be achieved when compared with those from conventional IVF.

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.