The presence of a sponsoring embryo in a batch of poor quality thawed embryos significantly increases pregnancy and implantation rate

OBJECTIVE: To evaluate quantitatively the effect of one good-quality (sponsoring) embryo in a batch of low-quality thawed embryos on the implantation and pregnancy rates (PR). DESIGN: Retrospective analysis of data. SETTING: Tertiary care center IVF clinic affiliated with a university medical school. PATIENT(S): Between March 1988 and April 1995, 392 IVF patients underwent a total of 440 thawing and ET cycles of 1,436 multicellular embryos. MAIN OUTCOME MEASURE(S): Implantation, clinical pregnancy, and multiple pregnancy rates. RESULT(S): In the absence of sponsoring embryos in the thawed batch of embryos, a PR of 9.8% with an implantation rate of 3.1% was achieved. In the presence of a single sponsoring embryo, the PR nearly doubled (18.2%), with a significantly higher implantation rate of 7.0%. Only singleton pregnancies were achieved in the absence of sponsoring embryos compared with 21.7% multiple pregnancies in the single sponsoring embryo group. CONCLUSION(S): The presence of a sponsoring embryo in a batch of poor quality thawed embryos is an important factor that significantly increased pregnancy and implantation rates. The optimal strategy for planning batches of multicellular frozen embryos is to include at least one sponsoring embryo in each batch when possible. We speculate that the sponsoring embryo may favorably influence the chances of low-quality embryos to undergo successful implantation.     

Selection and partial characterization of a Pseudomonas aeruginosa mono-rhamnolipid deficient mutant

A total of 29 women with Turner's syndrome (19 monosomy and 10 mosaic) had 68 cycles of oocyte donation that included 29 cycles of initial attempt and 39 cycles of subsequent attempts. Oral oestradiol valerate was used either in a variable dose (42 cycles) or in a constant dose (26 cycles) regimen for the endometrial preparation which was monitored by pelvic ultrasonography. The embryos/zygotes were transferred either fresh (50 cycles) or after cryopreservation (18 cycles) into the Fallopian tube (41 cycles) and uterine cavity (27 cycles) as appropriate. There were 28 clinical pregnancies including two sets of triplets resulting in a pregnancy rate of 41.2% per treatment cycle and an implantation rate of 17.1% per embryo transferred. The recipient's age, chromosomal constitution or associated uterine or tubal anomaly had no influence on the treatment outcome. The implantation and pregnancy rates were higher in the subsequent than initial cycles (22.6 versus 9.99%, P < 0.05; 51.3 versus 27.6%, P < 0.05). An endometrial thickness of > or = 6.5 mm was an important predictor of pregnancy but the endometrial echo pattern failed to predict the outcome. Although the total dose of oestradiol before embryo transfer was higher in the pregnant cycles than the non-pregnant ones and its gradation (< 50 mg, 50-100 mg, < 100 mg) influenced the implantation (3.4, 17.5, 26.3% respectively, P < 0.05) and pregnancy rates (10, 42.2, 61.5% respectively, P < 0.05), the effect was indirect by altering the endometrial thickness. The number of oocytes fertilized affected the pregnancy rate irrespective of the number of embryos transferred. The implantation and pregnancy rates were higher when fresh rather than frozen-thawed embryos were transferred (20.3 versus 8.2%, P < 0.05; 48 versus 22.2%, P < 0.05) but the route of transfer was of no statistical importance. The overall miscarriage rate was higher (50%), and was related to the presence of hypoplastic or bicornuate uterus and to a low oocyte fertilization rate.     

Embryo score to predict implantation after in-vitro fertilization: based on 957 single embryo transfers

The purpose of this study was to devise an embryo score to predict the likelihood of successful implantation after in-vitro fertilization (IVF). Unlike most studies dealing with the influence of embryo stage and morphology on pregnancy, our study was based on single rather than multiple embryo transfers. A total of 957 single embryo transfers were carried out. No delivery was obtained after any of the 99 transfers using 1-cell embryos or embryos obtained after delayed fertilization. In the remaining 858 transfers, the embryos had cleaved. Higher pregnancy rates were obtained with embryos displaying no irregular cells (11.7 versus 6.9%; P < 0.01) and embryos displaying no fragmentation (11.5 versus 8.1%; P < 0.05). The 4-cell embryos implanted 2-fold more often than embryos with more or less cells (15.6 versus 7.4%; P < 0.01). Based on these observations, we devised a 4-point embryo score in which embryos are assigned 1 point each if they (i) are cleaved, (ii) present no fragmentation, (iii) display no irregularities, and (iv) have four cells. Both pregnancy rate and take home baby rate were significantly correlated with embryo score. Each point of this score corresponds to a 4% increase in pregnancy rate. Interestingly, pregnancy rate was significantly lower in women aged > 38 years (8.2 versus 11.4%; P < 0.05), even though embryo quality was similar regardless of age. Single embryo transfer allowed us to define a simple and useful embryo score to choose the best embryo for transfer to optimize IVF and embryo transfer outcome. The use of this embryo score could decrease multiple pregnancies after multiple embryo transfers.     

Clinical evaluation and microbiology of oropharyngeal infection due to fluconazole-resistant Candida in human immunodeficiency virus-infected patients

The aim of the present study was to investigate pregnancy rates ensuing from transfer of embryos with multinucleated blastomeres. In our in-vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) programme, 1735 embryo transfers were performed from January 1, 1995 to August 31, 1996. In 136 of these transfers at least one embryo with one or more multinucleated blastomeres was present per transfer (study group). For each of these 136 transfers, two matched controls with transfer of exclusively mononucleated embryos were selected (control group). Matching was carried out according to age, method of fertilization (IVF or ICSI), number of transferred embryos and quality score of transferred embryos. In the study group, there were eight transfers of exclusively multinucleated embryos from which one pregnancy ensued and 128 transfers in which multinucleated and mononucleated embryos were transferred together leading to 23 pregnancies. The overall clinical pregnancy rate per transfer was 16.9% in the study group versus 28.7% in the control group (P = 0.01). The ongoing pregnancy rate per transfer was 13.2% in the study group versus 23.2% in the control group (P = 0.03). The implantation rate per transferred embryo was 6.0% in the study group versus 11.3% in the control group (P = 0.003). This study shows that embryos with one or more multinucleated blastomeres have a poorer implantation potential than embryos with mononucleated blastomeres. Transfer of embryos with multinucleated blastomeres should hence only be considered when insufficient numbers of embryos with only mononucleated blastomeres are present.     

Expression and molecular characterization of an enzymatically active recombinant human spumaretrovirus protease

A theoretical model is presented by which a true expression of pregnancy rate resulting from stimulated cycles can be calculated. This includes the transfer of both fresh and cryopreserved embryos. It is concluded that the total reproductive potential of a single cycle of stimulation can only be evaluated by including pregnancies arising from all fresh and frozen embryo transfers resulting from that cycle.     

A comparative analysis of embryos derived from routine in-vitro fertilization and subzonal microinsemination

Embryos obtained from patients undergoing routine in-vitro fertilization (IVF) and embryo transfer were compared with those undergoing subzonal microinsemination (SUZI) for male factor infertility. Overall, the proportion of cleaved embryos was significantly higher in the IVF group in comparison with the SUZI group at 48 h post-insemination [1533 out of 1609 (95.3%) versus 776 out of 952 (81.5%)]. The mean +/- SD grading score of the IVF-derived embryos of 3.61 +/- 0.50 was significantly better than that for SUZI of 2.97 +/- 0.86 (P < 0.0005) at the same time. The implantation rates following the replacement of IVF or SUZI embryos at 48 h were comparable: 14.3 and 10.0% respectively. However, the IVF embryo implantation rate of 15.1% at 72 h was significantly better than that following the replacement of SUZI embryos at either 48 (10.0%) or 72 h (8.0%). The replacement of SUZI-derived embryos at 48 h resulted in significantly higher pregnancy (25.0%) and implantation rates (10.0%) than at 72 h, with rates of 10.8 and 8.0% respectively. Similarly, the overall embryo quality deteriorated following in-vitro culture for up to 72 h. The clinical pregnancy loss rate (33.0%) was highest following the replacement of SUZI embryos at 72 h, although the data were limited. It is suggested that these data indicate that a combination of in-vitro manipulation, the injection of multiple spermatozoa into the subzonal space and probably the genomic capacity of spermatozoa derived from poor-quality semen may contribute to the poorer outcome of embryo development following SUZI. Prolonged in-vitro culture beyond 48 h appears to be deleterious to the development of SUZI cleaved embryos and the subsequent outcome of treatment, and hence should be avoided.     

Clinical outcome of cryopreserved human pronuclear stage embryos resulting from intracytoplasmic sperm injection

OBJECTIVE: To compare the survival rate and pregnancy rate (PR) of embryos from intracytoplasmic sperm injection (ICSI) or conventional IVF, which were cryopreserved at the pronuclear stage in cycles where fresh transfer was deferred. DESIGN: Comparative observational study. SETTING: University-associated IVF center. PATIENT(S): Ninety-nine patients who deferred ET and had all their embryos cryopreserved at the pronuclear stage after 153 oocyte retrievals. Thirty-nine patients had their oocytes inseminated by ICSI and 60 patients had conventional IVF insemination. INTERVENTION(S): All embryos were frozen-thawed at the two pronuclear stage and allowed to cleave for 2 days before transfer. MAIN OUTCOME MEASURE(S): Survival rate (morphologically intact after thaw), cleavage rate (cleaved by time of transfer), and the clinical PR after frozen ET. RESULT(S): In the ICSI group, 205 embryos were thawed for use in 57 frozen ETs; in the IVF group, there were 527 embryos thawed for use in 149 frozen ETs. There was no significant difference in any of the outcome measures by insemination method: survival rates (ICSI, 93.2%; IVF, 94.8%); cleavage rates (ICSI, 95.2%; IVF, 94.7%), and clinical PR (ICSI, 14.0%; IVF, 17.4%). CONCLUSION(S): Pronuclear embryos resulting from ICSI can be cryopreserved successfully, thawed, and the survival rate and PR are comparable to conventional IVF.     

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.     

Serum erythropoietin in chronic lymphocytic leukaemia

OBJECTIVE: To establish whether there is any improvement in pregnancy and implantation rates after administration of "low-dose," long-acting glucocorticoids during transfer of cryopreserved-thawed embryos. SETTING: An IVF unit in a university hospital. DESIGN: Prospective, randomized study. Ninety-nine consecutive transfer cycles of frozen-thawed embryos to the uterine cavity of randomly chosen women diagnosed as having tubal factor infertility only. Fifty-two patients underwent transfer of frozen-thawed embryos and received 0.5 mg of dexamethasone; 47 women (control group) did not receive the drug during transfer. PATIENTS: Normal ovulatory patients with tubal factor infertility. INTERVENTIONS: Oral dexamethasone administration before, during and after transfer of thawed embryos. MAIN OUTCOME MEASURES: Pregnancy and implantation rates. RESULTS: The pregnancy rate was 13.5% (7/52) in patients treated with the "low-dose" regimen of dexamethasone compared with 12.8% (6/47) in the control group. The implantation rate was similar. CONCLUSION: Our results demonstrated that the use of 0.5 mg dexamethasone for an immuno-suppressive effect, administered for a short period to patients diagnosed as having "pure" tubal factor infertility, did not improve the implantation or pregnancy rates.     

Effect of profound suppression of luteinizing hormone during treatment with gonadotrophin-releasing hormone analogue and purified follicle stimulating hormone upon development of cryopreserved embryos

In response to previously published evidence from monkeys, this study examined the influence of the degree of luteinizing hormone (LH) suppression during the follicular phase of the stimulation cycle, upon cryopreserved embryo survival and development. The LH concentration of the mid-follicular phase was assessed in 250 in-vitro fertilization (IVF) cycles treated with gonadotrophin-releasing hormone analogue (GnRHa) and either purified follicle stimulating hormone (FSH) or human menopausal gonadotrophin (HMG), and was related to the performance of cryopreserved embryos in 351 subsequent embryo transfer cycles. Rates of embryo survival, embryo development rates, implantation rates, and pregnancy rates were examined with respect to the LH concentration recorded in the mid-follicular phase. In contrast to experimental evidence from other primates, there was no significant influence of the follicular phase LH concentration upon any of the parameters examined.     

The effect of a propofol-based sedation technique on cumulative embryo scores, clinical pregnancy rates, and implantation rates in patients undergoing embryo transfers with donor oocytes

STUDY OBJECTIVE: To determine the effect, if any, of a propofol-based sedation technique on the reproductive outcomes of patients undergoing embryo transfers with donor oocytes. These ova recipients form a unique subgroup, whose clinical outcomes are unrelated to direct anesthetic effects on their reproductive tracts. DESIGN: Retrospective chart review. SETTING: A 1200-bed university medical center. PATIENTS: 117 patients who received fresh embryo transfer cycles between January 1991 and December 1995. MEASUREMENTS AND MAIN RESULTS: The anesthesia records of 106 women who donated ova were reviewed for propofol usage during the transvaginal needle aspiration of the ova. The medical records of the 117 patients who received these donated embryos were reviewed for cumulative embryo scores, clinical pregnancy rates, and implantation rates. Fourteen patients received ova from women who were sedated with fentanyl and midazolam during ovum retrievals, while 103 patients received ova from women who had been given fentanyl, midazolam, and propofol in doses of 1.87 mg/kg to 8 mg/kg. The pregnancy rate among all patients who received ova from women who received propofol (44 of 103 = 42.7%) was 14.1% greater than those whose ovum donors did not receive propofol (4 of 14 = 28.6). 78.6% of both propofol and non propofol-exposed groups had cumulative embryo scores of greater than 50. Among patients who became pregnant, 52.3% of propofol-exposed and 50% of nonpropofol-exposed cases had greater than 20% implantation rates. CONCLUSION: There is no evidence from our data that the administration of propofol during the aspiration of ovarian follicles for oocyte donation had a negative impact on the oocytes as measured by cumulative embryo scores, probability of a clinical pregnancy, or implantation rate.     

Transfer of cryopreserved embryos improved pregnancy rates in patients with damage to the functional integrity of the sperm membrane as measured by the hypo-osmotic swelling test

OBJECTIVE: To compare the pregnancy rates (PRs) after transfer of cryopreserved embryos in patients who have damage to the functional integrity of the sperm membrane as measured by the hypo-osmotic swelling test to those without this defect. DESIGN: Prospective clinical study. SETTING: University-associated IVF center. PATIENTS: Fifty-four patients enrolled in a matched prospective study to evaluate the effects of low HOS scores (<50%) on PRs after IVF-ET were followed to determine the PR after transfer of cryopreserved embryos. MAIN OUTCOME MEASURE: Clinical PRs and implantation rates. RESULTS: Fourteen patients with low hypo-osmotic swelling test scores underwent 21 frozen ET cycles, achieved for clinical pregnancies for a PR per cycle of 19.0% and an implantation rate of 7.1%. Twelve patients with normal hypo-osmotic swelling test scores underwent 21 frozen ET cycles, achieved five preganancies for a clinical PR per cycle of 23.8% and an implantation rate of 9.3%. CONCLUSION: Previous studies have demonstrated an adverse effect of low hypo-osmotic swelling test scores on PRs after IVF-ET despite normal fertilization. This adverse effect was not found in the transfer of cryopreserved embryos from males with hypo-osmotic swelling test scores. Further investigation is required to determine how cryopreservation improves the chances of implantation of these embryos.     

Improved oocyte quality is obtained with follicle stimulating hormone alone than with follicle stimulating hormone/human menopausal gonadotrophin combination

The aim of this study was to compare the efficacy of pure follicle stimulating hormone (FSH) with that of FSH/human menopausal gonadotrophin (HMG) combination in downregulated cycles. A total of 357 patients was evaluated retrospectively. Sixty percent of patients in the FSH group and 55% in the FSH/HMG group were new; the others were repeat patients. Ovulation was suppressed with leuprolide acetate in all patients, followed by either FSH (n = 218) or FSH/HMG (n = 119). There was no difference in patients' age, infertility factors, number of ampoules used, length of stimulation, oestradiol levels on day of human chorionic gonadotrophin (HCG) administration, number of oocytes recovered or the number of embryos transferred. Also, nuclear maturity at aspiration and fertilization rates were not different between the two groups. FSH stimulation resulted in a significantly higher percentage of mature oocytes that showed the typical 'mature' morphological characteristics (P < 0.0001). The clinical pregnancy rates per transfer were 40 and 28% in patients stimulated with pure FSH and FSH/HMG respectively (P < 0.05). The significantly higher number of immature oocytes matured in vitro in the FSH/HMG group (P = 0.001) suggests a possible effect on in-vitro maturation, due to luteinizing hormone present in HMG. The difference in mature oocyte quality may be an important determinant in the higher pregnancy rates for the FSH-stimulated patients.     

The optimal number of embryos to be transferred in shared oocyte donation: walking the thin line between low pregnancy rates and multiple pregnancies

There has been growing concern about the number of multiple gestations resulting from assisted reproductive technologies. For in-vitro fertilization (IVF), there are guidelines concerning the number of embryos to be transferred. In oocyte donation, however, there is a paucity of studies addressing this issue and common practice is extrapolated from standard IVF procedures. This may not be correct since endometrial receptivity has been shown to be altered in oocyte donation. Thus the purpose of this study was to assess the optimal number of embryos to be transferred in oocyte donation. The study population included 254 patients with ovarian failure who underwent a total of 601 embryo transfers in a single shared oocyte donation programme. Pregnancy rates (PRs), multiple pregnancies, triplet pregnancy rates, and implantation rates were evaluated according to the number of embryos transferred. A significant linear increase in PRs was noted with the increasing number of embryos transferred up to five (11.1% for one embryo, 36.7% for five embryos). Multiple pregnancies increased significantly from 15.8% for two embryos transferred, to 44.4% for five embryos. The rate of triplet pregnancies also increased from 2.7% for three embryos transferred, to 8.3% for five embryos. Optimization of the number of embryos to be transferred is discussed.     

Transrectal electroejaculation combined with in-vitro fertilization: effective treatment of anejaculatory infertility due to spinal cord injury

Infertility due to spinal cord injury (SCI) in young men is a frequent complication of their injury. When the simpler methods of management of the erectile and ejaculatory dysfunction that invariably follow the more severe types of SCI are not effective, then semen production by transrectal electroejaculation (TREE) combined with in-vitro fertilization (IVF) and embryo transfer is effective. A retrospective analysis is presented of data on the treatment and outcome of 35 couples who wished to have a family but in whom the male partner had suffered SCI. These 35 couples had 71 attempts at IVF with spermatozoa obtained following TREE. Normal fertilization and cleavage of the embryos occurred in 48.2% of the oocytes. Fresh embryos were transferred in 54 cycles and frozen-thawed embryos in 14 cycles. In all, 18 clinical pregnancies were achieved in 54 fresh and 14 frozen embryo transfer cycles, with a live birth rate of 16.5% (14/85) per treatment cycle started, 20.6% (14/68) per transfer cycle and 40.0% (14/35) per couple who started treatment, in a mean of 1.9 transfer cycles. We conclude that TREE combined with IVF and embryo transfer is an effective treatment for the infertility problems associated with SCI.     

Opportunity for obligatory declaration of HIV infection from its serologic stage

Although in-vitro fertilization treatment is doctor-led, many of its steps are performed by nurses. The embryo transfer step, however, is performed exclusively by doctors in the majority of units. In our unit, doctors performed embryo transfers from June 1994 until December 1995 (period I). From January 1996 until May 1997 (period II) the nurses, after appropriate training, performed the procedure. When they experienced difficulties during the mock transfer performed immediately before the real transfer, or if they were not available to do the procedure, a doctor performed it. In period I, 488 embryo transfers were performed (all by doctors), with a pregnancy rate per transfer of 35% and an implantation rate of 16%. In period II, 522 embryo transfers were performed. Nurses performed 371 (71%) and doctors 151 (29%) of the procedures. The pregnancy rate per nurse-transfer was 40.2% and per doctor-transfer 41%. The corresponding implantation rates were 16.9% and 17%. None of these differences were statistically significant (P > 0.05). These data indicate that, with appropriate training and medical back-up, nurses can perform the majority of embryo transfers with ease and outcome comparable to that of doctor embryo transfer.     

The selection criteria on an IVF program can remove the association between maternal age and implantation

BACKGROUND: 1190 consecutive in vitro fertilization (IVF) treatment cycles from the Southampton University/BUPA Chalybeate unit, spanning a four year period, were studied retrospectively in order to assess the relationship between maternal age and implantation. Our aim was to evaluate the hypothesis that the number of transferred embryos can be determined by age alone. METHOD: The cases were allocated to two age groups, Group 1 was composed of patients of less than or equal to 35 years of age and Group 2 of patients greater than 35 years of age. RESULTS: We found that the selection criteria used in our programme for abandoning treatment cycles led to significantly more older patients being excluded from oocyte collection (p < 0.001). The patients from both groups that progressed to oocyte collection and embryo transfer showed no significant difference in embryo implantation. The overall implantation rate (12.4%) and clinical pregnancy rate per embryo transfer (22.8%) were achieved by being able to transfer comparable numbers of embryos in both age groups and in spite of the younger age group having a significantly better quality of transferred embryos. CONCLUSION: Although advancing maternal age predisposes to a reduced chance of success from IVF treatment, maternal age alone was not a useful predictor of embryo implantation or endometrial receptivity in completed IVF treatment cycles.     

Cryopreservation of mouse spermatozoa from inbred and F1 hybrid strains

Mouse epididymal spermatozoa from inbred(BALB/c, C3H/He, C57BL/6N, CBA/JN and DBA/2N) and F1 hybrid (B6C3F1, BDF1 and CDF1) strains suspended in cryopreservation solution (18% raffinose and 3% skim milk in distilled water) were frozen and stored at -196 degrees C. After thawing at room temperature, sperm motility and fertilizing ability were examined. Spermatozoa from all of the strains were successfully frozen, although the motility and the fertilization rates of frozen-thawed spermatozoa (the proportions of the fresh oocytes from Jcl:ICR strain which developed to pronuclear oocytes and 2-cell embryos after insemination by frozen-thawed spermatozoa) varied among strains (motility: 23% for C57BL/6N to 62% for DBA/2N; fertilization rates: 26% for C57BL/6N to 89% for DBA/2N). Nearly all 2-cell embryos fertilized by frozen-thawed spermatozoa were transferred to the oviducts of pseudopregnant recipients and 35-62% of 2-cell embryos developed into normal young.     

Combined fresh and frozen embryo transfer resulting in a twin delivery

We report the delivery of non-identical twins resulting from the combined transfer of one fresh and one frozen embryo to a 31 year old patient. To our knowledge, this is the first reported case where both a fresh and a frozen embryo implanted in the same cycle led to non-identical twins. We conclude that supernumerary embryos after in-vitro fertilization should be frozen and used in subsequent cycles, with implantation potentials as high as fresh embryos. The possibility of mixing fresh and frozen embryos, though rarely needed, should be considered, particularly when there is only one fresh embryo available for transfer.     

Effects of reducing insemination time in human in vitro fertilization and embryo development by using sibling oocytes

PURPOSE: Recent studies showed a beneficial effect of reducing the time of sperm-oocyte interaction on fertilization, division, and implantation rates of the oocytes obtained from randomized patients. In the present study, the effects of reduced insemination time on fertilization and embryo development were evaluated by using sibling oocytes from the same patient. METHODS: A total of 464 oocytes from 36 patients was randomly allocated to be inseminated for either 1 hr (reduced) or 18 hr (regular). RESULTS: Fertilization rates were not significantly different between reduced (135/229; 59%) and regular (150/235; 64%) groups. Cleavage rates and embryo quality were similar in both groups. A total of 135 embryos (73 from the reduced and 62 from the regular group) was transferred to 36 patients. Thirty-four embryos implanted in 18 patients (25.2% implantation and 50.0% pregnancy rates). CONCLUSIONS: Fertilization, cleavage, and embryo development from 1-hr insemination is comparable, not superior, to those from an 18-hr insemination time, which is commonly used in in vitro fertilization programs. These data suggest that reduced insemination time can be used during in vitro fertilization to avoid unnecessarily longer exposure to spermatozoa.