Polyspermy: effect of varying stimulation protocols and inseminating sperm concentrations

Benefit of intracytoplasmic sperm injection in patients with a high incidence of triploidy in a prior in vitro fertilization cycle

OBJECTIVE

To test the hypothesis that intracytoplasmic sperm injection (ICSI) overcomes a high incidence of tripronucleate zygotes resulting from standard insemination in a previous cycle.

DESIGN

A retrospective analysis of matched-pair cycles.

SETTING

Assisted reproductive technologies (ART) program of Brigham and Women's Hospital.

PATIENT(S)

Ninety-five patients with a > or = 20% incidence of tripronucleate zygotes in an IVF cycle with use of ICSI in a subsequent attempt.

INTERVENTION(S)

Cycles with either standard insemination or ICSI.

MAIN OUTCOME MEASURE(S)

Incidence of diploid (2pn) and triploid (3pn) zygotes and number and quality of embryos obtained.

RESULT(S)

Patient age, ampules of gonadotropin used, peak E2, number of follicles at hCG trigger, and total number of oocytes were all significantly higher in the ICSI cycles, but the number of mature oocytes did not differ. After ICSI, the percentage of 2pn was higher (65.0% vs. 34.1%) and the percentage of 3pn was lower (5.0% vs. 33.9%) than after IVF, and more diploid embryos were obtained with ICSI (5.5 +/- 3.7 vs. 3.4 +/- 2.2 [mean +/- SD]). There was no difference in embryo quality between the two groups.

CONCLUSION(S)

ICSI appears beneficial in women with a high 3pn occurrence from IVF because it increases the number of diploid zygotes without affecting embryo quality.

Aneuploid analysis of tripronuclear zygotes derived from in vitro fertilization and intracytoplasmic sperm injection in humans

This study demonstrates that the diploid ratio of tripronuclear zygotes after intracytoplasmic sperm injection (ICSI) is significantly higher as compared with that after conventional IVF; the extra pronucleus of tripronuclear zygotes after ICSI are mostly from the second polar body, not from sperm.

Analysis of factors associated with multinucleate formation in human IVF

This study was carried out to analyse if some of the sperm parameters assessed by computer-aided sperm analysis (CASA) are associated with multinucleate formation in human in vitro fertilization (IVF). In the present study, 137 IVF-embryo transfer (ET) treatment cycles in which pronucleate formation could be observed were enrolled. Sperm parameters after swim-up were assessed using CASA and strict criteria. Thirty-two (2.3%) of 1368 oocytes fertilized were judged as multinucleate formation, which occurred in 25 of 137 IVF-ET treatment cycles, giving the incidence of 18.2%. The factors associated with multinucleate formation were analysed. There were significant differences of the numbers of oocytes collected (13.9 vs. 9.2; p=0.028), fertilization rate (88.8% vs. 71.9%; p=0.011), curvilinear velocity (VCL) (162.7 microm/sec vs. 149.1 microm/sec; p=0.034), average path velocity (VAP) (100.3 microm/sec vs. 93.1 microm/sec; p=0.016), and amplitude of lateral head displacement (ALH) (5.9 microm vs. 5.3 microm; p=0.046) between 25 cycles with multipronucleate formation and 112 cycles with two pronucleate formations. However, there were no significant differences of women's age or the number of sperm inseminated between the two groups. These findings suggest that prediction of multinucleate formation in human IVF might be possible in patients when the number of oocytes collected is higher and sperm motility parameters after swim-up are faster. However, prevention of multinucleate formation seems to be unnecessary because a higher successful IVF-ET outcome is expected as a result of the excellent fertilization rate in these patients.

Fertilization abnormalities following human in vitro fertilization and intracytoplasmic sperm injection

Fertilization abnormalities are commonly encountered following in vitro fertilization. The widespread introduction of assisted fertilization methods has rapidly led to a changes in both the incidence and types of these aberrations. Such abnormalities can be identified by careful morphological evaluation at the early zygote stage, of pronuclei as well as of polar body formation, and may be confirmed by cytogenetic assessment. The recognition and understanding of fertilization abnormalities have led to the development of novel techniques aimed at preventing them, as well as recent bold attempts at correction. Removal of one pronucleus may allow some triploid embryos to revert to a normal diploid stage. These new developments should provide insight into the understanding of parthenogenesis, androgenesis, and gynogenesis in the human. Microsc. Res. Tech. 61:358-361, 2003.

Perivitelline space: does it play a role in blocking polyspermy in mammals?

The perivitelline space of mammalian oocytes changes in size and composition during preimplantation development. Often overlooked in the past, this space contains a hyaluronan-rich extracellular matrix prior to fertilization and a cortical granule envelope following release of the cortical granules at fertilization. The hyaluronan-containing matrix of unfertilized oocytes is well developed in some species such as opossums and humans but is scant in rodents including the hamster and mouse. The significance of the hyaluronan-rich matrix, which attaches to the plasma membrane of the oocytes, is not fully understood. However, hyaluronan, which can inhibit membrane fusion, is present in the perivitelline space (PVS) of unfertilized oocytes and must be negotiated by the fertilizing sperm. Following fertilization, the cortical granule envelope forms as the cortical granules disperse, thereby causing the PVS to increase significantly in size. Calcium is important in the dispersion of the cortical granules following exocytosis. Once formed, the cortical granule envelope in some species is about the same thickness as the zona pellucida, but it is not readily visualized unless it is stained with fluorescent probes or examined ultrastructurally after following stabilization with ruthenium red. The envelope contains proteins that remain in the PVS until the time of blastocyst hatching. Although little work has been done on the functions of the cortical granule envelope, several studies are consistent with the idea that it plays a role in blocking polyspermy. While nicotine increases polyspermy in sea urchins, its effects on polyspermy in human smokers have not been characterized, but could be addressed in human in vitro fertilization labs.

Increased fertilization and pregnancy rate in polypronuclear fertilization cycles in in vitro fertilization-embryo transfer

OBJECTIVE

To compare fertilization and pregnancy rates between cycles with polypronuclear fertilizations and cycles with normal fertilizations.

DESIGN

In vitro fertilization-embryo transfer (IVF-ET) cycles in which oocytes were retrieved were divided into two groups according to the nature of fertilization.

PATIENTS

All patients were participants of our IVF-ET program.

RESULTS

A significantly higher fertilization rate was found in the polypronuclear fertilization cycles (61% versus 36.6%) and also an improved pregnancy rate (47.5% versus 19.6%) and per embryo transfers (53% versus 28.8%). The vast majority of polypronuclear fertilizations occurred in mature oocytes.

CONCLUSION

We believe that the increased receptability of the oocytes improves fertilization and conception rates. The polypronuclear fertilization is an extreme expression of such improved receptibility and should be considered as an encouraging sign for conception.

Dispermic fertilization of human oocytes

Regardless of whether fertilization occurs in vivo or in vitro, polyspermic penetration of the human oocyte is a not infrequent cause of reproductive failure. This report describes the occurrence of human eggs fertilized by two spermatozoa and the variable developmental potentials expressed by the resultant embryos. The cellular and subcellular events that characterize the pronuclear and early cleavage stages of preimplantation embryogenesis are discussed with respect to the ability of such embryos to progress to implantation.

Super high estradiol response to gonadotropin stimulation in patients undergoing in vitro fertilization

The likelihood of establishment of a term pregnancy from in vitro fertilization (IVF) is related to the estradiol (E2) pattern and peak level. To examine the influence of super high E2 peak levels (greater than or equal to 2000 pg/ml), we reviewed the clinical outcomes of all IVF cycles with follicular phase E2 levels greater than 2000 pg/ml from May 1982 through June 1987. Among 1651 IVF cycles initiated during this time, 102 cycles (6.2%) had super high E2 levels. Twenty-seven of these cycles occurred in 34 IVF attempts in 12 women. Stimulation was performed with human menopausal gonadotropin (hMG) in 96 cycles and follicle-stimulating hormone (FSH) in 6 cycles. A mean of 9.3 +/- 0.7 oocytes per cycle was recovered, of which 5.5 +/- 0.5 fertilized and underwent cleavage. In 11 cycles, with a mean of 6.8 oocytes recovered, none fertilized. Polyploid fertilization occurred in 23 of 90 cycles (25.6%), and 40 of 558 fertilized oocytes (7.2%). From these cycles, 10 clinical pregnancies (9.8%) have resulted: 6 pregnancies in 59 cycles with luteal-phase progesterone support (10.2%) and 4 pregnancies in 31 cycles without luteal-phase progesterone support (12.9%). Among the 1549 cycles with peak E2 levels less than or equal to 2000 pg/ml, 143 (9.2%) resulted in clinical pregnancies. We conclude that there is a small subset of patients who will have super high E2 responses to gonadotropin stimulation and that there is a tendency to stimulate repetitively in this fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine profile of follicles containing oocytes with subsequent polyploid fertilization

In an attempt to identify oocytes at risk for polypronuclear fertilization, follicular fluids were obtained retrospectively that contained oocytes that fertilized normally and abnormally. Whenever possible, each patient served as her own control during the same stimulation cycle. Twenty-six of 169 patients had oocytes that became polypronuclear, and of those 26, 21 had oocytes that fertilized and cleaved normally. Follicular fluids were analyzed for estradiol, progesterone, androstenedione, transferrin, and insulin. Insulin levels were noted to be significantly elevated (P less than 0.05) in the polypronuclear group when compropose that insulin, a known growth factor for granulosa cells cultured in vitro, when present in excessive concentrations may predispose to polypronuclear fertilization.

The effect of polyploidy on embryo cleavage after in vitro fertilization in humans

The effect of polyploidy on the early development of human embryos is unknown. This study compares the early development of 90 polyploid and 275 diploid human embryos conceived in vitro. Between May 1983 and January 1986, 3081 oocytes were recovered during 631 cycles of laparoscopy for in vitro fertilization (4.9 oocytes/cycle); 1924 oocytes (62.4%) fertilized. There were 90 oocytes with more than two pronuclei (4.7% of fertilized oocytes), identified in 72 cycles (11.4% of cycles). In these cycles, the proportion of diploid oocytes (n = 275) that cleaved (cleavage rate) (92.7%) was significantly greater than the proportion of polyploid oocytes (n = 90) that cleaved (65.5%) (P less than 0.001). The cleavage rate for all diploid oocytes (n = 1834) was 90.4%. There was no significant difference in the stage of development (number of blastomeres; mean +/- standard deviation [SD]) on the day of embryo transfer between diploid (4.3 +/- 2.1) and polyploid (4.1 +/- 2.1) embryos that cleaved, but a plot of the frequency distribution of cleavage stages revealed that significantly more polyploid than diploid embryos had an uneven number of blastomeres at that time (33% versus 8%, respectively; P less than 0.001). Polyploidy confers an immediate developmental disadvantage; one third of polyploid embryos fail to cleave, and those that do divide demonstrate more asynchronous divisions.

Relationships between polypronuclear fertilization and follicular fluid hormones in gonadotropin-treated women

Similar incidences of congenital abnormalities in in vitro fertilization and embryo transfer (IVF-ET) pregnancies and births in the general population have not supported earlier concerns that IVF may increase chromosomal aberrations. Nevertheless, polypronuclear fertilization is a common, undesirable, and poorly understood outcome of IVF. We evaluated hormone levels in 20 follicular fluids that were associated with mature oocytes that have fertilized abnormally (greater than or equal to pronuclei) and compared them to follicles with mature oocytes that cleaved normally, fertilized but failed to cleave, or did not fertilize. Progesterone (P), androstenedione, estradiol, percent free estradiol, sex hormone-binding globulin, insulin, and prolactin were measured. P levels were significantly higher in follicular fluids associated with oocytes that fertilized abnormally than in the other groups. Levels of the other hormones were similar in all the study groups. We conclude that IVF of oocytes from highly luteinized follicles as judged by P levels may result in polypronuclear fertilization.

Effect of the number of inseminating sperm and the follicular stimulation protocol on in vitro fertilization of human oocytes in male factor and non-male factor couples

The effect of sperm concentration and follicular stimulation protocol on in vitro fertilization of human oocytes is not well established. Comparison was made of three inseminating concentrations (250,000, 375,000, and 500,000 progressively motile sperm/oocyte) and three protocols (human menopausal gonadotropin [hMG], clomiphene citrate [CC], and combination hMG/CC) on the fertilization rate of mature and immature oocytes in couples with male factor and non-male factor infertility. In non-male factor couples, total fertilization rates for CC, hMG, and hMG/CC were 70.3%, 54.5%, and 68.8%, respectively, while total fertilization rates at the varying number of inseminating sperm were not significantly different. Mature oocytes were more likely than immature oocytes to fertilize. Among semen male factor couples, there was no difference in fertilization by stimulation protocol; however, insemination with the higher number of inseminating sperm resulted in an increased fertilization rate.