Pregnancy following fertilization of zona-free, coronal cell intact human ova: Case Report

A ZP1 gene mutation in a patient with empty follicle syndrome: A case report and literature review

Genuine empty follicle syndrome (gEFS) is a rare cause of female infertility; it is defined as the presence of cumulus-oocyte complexes (COCs) in follicular fluid but the absence of oocytes after denudation in an in vitro fertilization (IVF) programme. Mutations in one of the four genes encoding zona pellucida (ZP) proteins have been implicated in gEFS. The objectives of the present study were to explore the molecular basis of idiopathic infertility in a 35-year-old woman with gEFS (observed after four ovarian retrievals), compare her phenotype and genotype with those of other patients described in the literature, and discuss therapeutic approaches that could be adopted by reproductive health centres in this situation. Sequencing of the ZP genes revealed a new homozygous missense variant in ZP1: c.1097G > A;p.(Arg366Gln). The variant is located in the ZP-N domain, which is essential for ZP protein polymerization. An immunohistochemical assessment of an ovarian biopsy confirmed the absence of ZP1 protein. The novel variant appears to prevent ZP assembly, which would explain the absence of normal oocytes after denudation in our patient (and despite the retrieval of COCs). ZP gene sequencing should be considered for patients with a phenotype suggestive of gEFS. An etiological genetic diagnosis enables appropriate genetic counselling and a switch to an IVF programme (with a suitable denudation technique) or an oocyte donation programme.

Functional substitution of zona pellucida with modified sodium hyaluronate gel in human embryos

PURPOSE

Zona pellucida-free (ZP-free) embryos often fail to achieve good developmental outcomes and are routinely discarded in assisted reproductive laboratories. Existing attempts to rescue ZP-free embryos are not widely used due to operational complexity and high technical requirements. To handle cases with missing ZP, we applied modified sodium hyaluronate gel (MSHG) to embryo culture to determine if it can function as a substitute for human zona pellucida.

METHODS

The developmental process and the blastocyst formation rate of embryos were analyzed in both mouse and human. The first clinical application of MSHG was reported, and the pregnancy outcome was continuously followed up.

RESULTS

Human and mouse ZP-free embryos cultured with MSHG showed a blastocyst formation rate similar to ZP-intact embryos. MSHG improves blastocysts formation rate by maintaining blastomere spatial arrangement at early stages. Compared to ZP-free embryos, the proportion of tetrahedrally arranged blastomeres at the 4-cell stage increased significantly in embryos cultured with MSHG in humans. A ZP-free blastocyst cultured in MSHG with the highest score was successfully implanted after day 5 transplantation and developed normally.

CONCLUSION

These data demonstrate that MSHG can substitute the function of zona pellucida and rescue human ZP-free embryos during assisted reproductive technology.

An Alternative Way to Improve Mammalian Embryo Development In Vitro: Culture of Zona Pellucida-Free Embryos

An increasing number of data proves that the presence of the zona pellucida is not essential to mammalian embryo production, including maturation, fertilization, and embryo culture. In fact, the structure of the zona pellucida of in vitro-produced embryos differs significantly from its in vivo counterpart, influencing metabolism and requiring disproportionate efforts to crack open at the time of hatching. This review aims to focus attention on this field and stimulate research in zona-free embryo culture. In domestic animals, extensive application of purpose-designed culture systems for zona-free embryos proved the feasibility of this approach. It may open new possibilities and increase efficiency in both transgenic research and human-assisted reproduction.

Embryological Characteristics of Human Oocytes With Agar-Like Zona Pellucida and Its Clinical Treatment Strategy

Zona pellucida (ZP) abnormalities are the cause of low fertility or infertility, agar-like ZP is more common in abnormal ZP. The purpose of this exploration is to systematically analyze the fertilization competence of agar-like ZP oocytes, the development characteristics of subsequent embryos as well as the results of embryo transfer, aiming to explore effective clinical treatment strategies. A total of 58 patients with agar-like ZP were set as the case group and the control group involved 3866 patients, in which the patients' oocytes presented normal ZP. BMI, basal hormone levels, and hormone levels were similar in both groups. The case patients suffered significantly longer infertility years than control (p<0.05), and most patients were diagnosed with pelvic inflammatory diseases. A distinct difference was observed in the structure of oocyte corona cumulus complexes between the two groups. The embryo development parameters, which include the rates of cleavage, high-quality embryo, blastocyst, and high-quality blastocyst in the case group were greatly lower than that in the control group (p<0.05). The rates of cumulative clinical pregnancy and live birth were comparable between the two groups. In the subsequent follow-up, thirty-four of the 58 patients receiving intracytoplasmic single sperm injection (ICSI) or early rescue ICSI (R-ICSI) treatment successfully gave birth to babies, and all of the newborns were with no neonatal defects. In addition, the fertilization rate of the R-ICSI group was significantly lower than that of the ICSI group (p<0.05). The occurrence of agar-like ZP impairs the development competence of human oocytes, however, the human oocytes with agar-like ZP can develop into healthy offspring, and an ICSI regimen is the optimal treatment strategy for them.

Organelle targeting using a fluorescent probe that selectively penetrates the zona pellucida

The characteristics of oocytes, which are female germ cells, have not been studied using optical materials. The structural layers (zona pellucida, ZP) around oocytes make it difficult to deliver drugs aimed at treating infertility. Here, we investigated whether the fluorescent probes sulforhodamine, fluorescein 5(6)-isothiocyanate, tetramethylrhodamine isothiocyanate, cyanine 3 carboxylic acid, and cyanine 5 carboxylic acid penetrate oocytes. By targeting the ZP layer of the oocyte, the characteristics of the model drug, a fluorescent probe, were analyzed, and the position of the probe in the oocyte was confirmed for differences in the characteristics. Penetration of the ZP and delivery into the cytoplasm differed between the fluorescent probes. This was due to their different physiochemical properties, including hydrophobicity (contact angle and surface tension), surfactant activity, and electrical charge. Among the fluorescent probes delivered to cytoplasm, unlike TRITC, Cy3 and Cy5 perturbed oocyte development. These results suggest that in oocytes with high physical barriers (cell membrane, zona pellucida), the delivery efficiency can be estimated by considering the properties (molecular weight and structure, solubility and functional structure, etc.) of the drug. In addition, it suggests that an encapsulated or bound carrier of a drug with properties similar to that of a fluorescent probe can be efficiently delivered into oocytes.

Live birth in a complete zona-free patient: a case report

OBJECTIVE

To report a live birth from a patient with complete zona-free oocytes due to abnormal zona production and to reveal full time-lapse blastocyst development footage of its originating embryo.

METHODS

A 34-year-old woman presented with a history of failed fertilization via standard in vitro fertilization insemination and a potential absence of zona pellucida. A total of 3 intracytoplasmic sperm injection cycles were undertaken with all oocytes collected being zona-free. Embryos created in the initial 2 cycles were cultured in the G1+/G2+ sequential media in a benchtop incubator. During the final successful cycle, the culture strategy was shifted to single step media (G-TL) in an Embryoscope+ incubator.

RESULTS

The first 2 attempts led to a biochemical pregnancy or no blastocyst available for transfer. In the third cycle, 13 out of 24 collected oocytes were subjected to injection, with 4 being normally fertilized. Two blastocysts were subsequently formed, in which one was cryopreserved and the other transferred. A live baby girl (1570g) was subsequently delivered at 34 weeks of gestation by cesarean section.

CONCLUSION

Live birth can be achieved for patients with zona production deficiency. Adjustment in ovarian stimulation and subsequent embryo culture strategies may have potentially contributed to the success of the 3rd cycle.

Role of diagnostic intracytoplasmic sperm injection (ICSI) in the management of genetically determined zona pellucida-free oocytes during in vitro fertilization: a case report

PURPOSE

To report the utilization of diagnostic intracytoplasmic sperm injection (D-ICSI), an ICSI cycle performed in the natural cycle, to obtain information about embryo development potential after sperm injection into zona pellucida (ZP)-free oocytes.

MATERIALS AND METHODS

We report the case of a couple with primary unexplained infertility with a history of previous failed, in vitro fertilization intracytoplasmic sperm injection (IVF-ICSI) cycles characterized by the presence of ZP-free oocytes. Whole exome sequencing (WES) was carried out to analyse the possible genetic basis of oocyte abnormality.

RESULTS

Diagnostic ICSI provided information about the embryo development potential from ZP-free oocytes and allowed better planning of the subsequent ICSI cycle. WES revealed that the absence of ZP was likely to be due to a new (ZP1) mutation. The subsequent ICSI cycle resulted in the delivery of a healthy baby.

DISCUSSION

To the best of our knowledge, our report is the first to describe the use of D-ICSI to determine the feasibility of embryo development and implantation in a patient with ZP1 mutation, resulting in the subsequent delivery of a healthy baby. We used 'diagnostic' ICSI in the normal menstrual cycle to explore the feasibility of embryo development after sperm injection into ZP-free oocytes. Our results may expand the spectrum of diagnostic procedures associated with unexplained infertility.

Live birth of twins derived from zona-free oocytes

OBJECTIVE

To report a live birth of twins from autologous zona-free oocytes.

DESIGN

Case report.

SETTING

Reproductive endocrinology and infertility private practice and ambulatory in vitro fertilization (IVF) center.

PATIENT(S)

A 34-year-old woman, gravida 0, with 100% zona-free oocytes.

INTERVENTION(S)

IVF with intracytoplasmic sperm injection (ICSI), blastocyst culture, and fresh embryo transfer.

MAIN OUTCOME MEASURE(S)

Fertilization, blastocyst development, and live birth.

RESULT(S)

A 34-year-old woman, gravida 0, conceived through IVF using autologous zona-free oocytes. The 11 retrieved oocytes were zona-free, from which eight were inseminated with ICSI; two embryos were transferred at morula and blastocyst stage, resulting in a twin pregnancy delivered at an estimated the gestational age of 37 weeks and 1 day.

CONCLUSION(S)

Patients with the rare condition of 100% zona-free oocytes maintain the potential for pregnancy after careful micromanipulation of the oocytes. Caution is recommended on the number of embryos selected for transfer to reduce the risk of multiple gestation.

Time-lapse monitoring of zona pellucida-free embryos obtained through in vitro fertilization: a retrospective case series

OBJECTIVE

To report time-lapse monitoring of human oocytes in which the damaged zona pellucida was removed, producing zona-free (ZF) oocytes that were cultured until the blastocyst stage in time-lapse incubators.

DESIGN

Retrospective case series.

SETTING

Private infertility clinic.

PATIENT(S)

Infertile patients (n = 32) undergoing minimal ovarian stimulation or natural cycle IVF treatment between October 2012 and June 2014.

INTERVENTION(S)

Intracytoplasmic sperm injection (ICSI) fertilization of ZF oocytes, prolonged embryo culture in time-lapse incubators, elective vitrification, and subsequent single vitrified-thawed blastocyst transfer (SVBT).

MAIN OUTCOME MEASURE(S)

Rate of fertilization, cleavage and blastocyst development, live-birth rate per SVBT cycle.

RESULT(S)

In spite of advanced maternal age (39 ± 4.2; range, 30-46 years), good fertilization (94%), cleavage (94%), and blastocyst development rates (38%) were reached after fertilization and culturing of ZF oocytes/embryos. All thawed ZF blastocysts survived, and up to this date seven SVBT transfers were performed, yielding three (43%) term live births with healthy newborns.

CONCLUSION(S)

Time-lapse imagery gives a unique insight into the dynamics of embryo development in ZF embryos. Moreover, our case series demonstrate that an oocyte with a damaged zona pellucida that has been removed could be successfully fertilized with ICSI, cultured until blastocyst stage in a time-lapse incubator and vitrified electively for subsequent use.

Are zona pellucida genes involved in recurrent oocyte lysis observed during in vitro fertilization?

PURPOSE

Complete oocyte lysis in in vitro fertilization (IVF) is a rare event, but one against which we remain helpless. The recurrence of this phenomenon in some women in each of their IVF attempts, regardless of treatment, together with the results of animal experiments led us to investigate the possible involvement of the genes encoding for the glycoproteins constituting the zona pellucida (ZP).

PATIENTS & METHODS

Over the last ten years, during which we treated over 500 women each year, three women suffered recurrent oocyte lysis during their IVF attempts in our Centre for Reproductive Biology. For each of these three cases, we sequenced the four genes and promoter sequences encoding the glycoproteins of the ZP. The sequence variations likely to cause a change in protein expression or structure, were investigated in a control group of 35 women who underwent IVF without oocyte lysis and with normal rates of fertilization.

RESULTS & CONCLUSION

We found no mutations in the ZP genes sequenced. Only some polymorphisms present in the control group and in the general population were detected, excluding their specific involvement in the phenotype observed. Thus, although we suspected that complete oocyte lysis was due to a genetic cause, it did not seem possible to directly incriminate the genes encoding the proteins of the ZP in the observed phenotype. Further study of the genes involved in the processing and organization of ZP glycoproteins may allow elucidation of the mechanism underlying recurrent oocyte lysis during in vitro fertilization.

Embryological, clinical and ultrastructural study of human oocytes presenting indented zona pellucida

Human oocyte dysmorphisms attain a large proportion of retrieved oocytes from assisted reproductive technology (ART) treatment cycles. Extracytoplasmic defects involve abnormal morphology of the zona pellucida (ZP), perivitelline space and first polar body. The aim of the present study was to describe a novel dysmorphism affecting the ZP, indented ZP. We also evaluated the clinical, embryological and ultrastructural features of these cases. We evaluated all ART treatment cycles during 7 consecutive years and found 13 treatment cycles (six patients) with all oocytes presenting an indented ZP. In addition, these oocytes presented total or partial absence of the perivitelline space, absence of resistance to ZP and oolemma penetration during microinjection, and low ooplasm viscosity during aspiration. This novel described dysmorphism was recurrent and attained all oocytes in three cases that had more than one treatment cycle. When compared with controls, data showed significant low oocyte maturity (42% versus 81.6%) and high cycle cancellation (30.8% versus 8.5%) rates, normal degeneration (3.4% versus 6.3%) and fertilization rates (69% versus 69.5%), and low pregnancy (15.4% versus 33.3%) and live-birth delivery (7.7% versus 27.7%) rates per cycle. Ultrastructure analysis revealed a zona pellucida structure with large empty electrolucent regions, an outer ZP layer with an indented surface with protuberances and a thick inner ZP that obliterated the perivitelline space. There was evidence of exocytosis of ZP material by the oocyte. In conclusion, oocytes with this novel described dysmorphism (indented ZP) are associated with low maturity, pregnancy and live-birth delivery rates.

Infertility and Immunocontraception based on zona pellucida

The zona pellucida (ZP) is an extracellular matrix surrounding ovarian oocytes, ovulated eggs and preimplantation embryos. It plays several important roles at different stages of reproduction. Its constituent glycoproteins are expressed specifically in the ovary. It is thus possible to produce autoantibodies to ZP proteins that interfere with reproductive functions including folliculogenesis, fertilization and implantation. First, this article describes the history of anti-ZP antibodies detected in women with idiopathic infertility. Second, the current relationship between anti-ZP antibodies and infertility is discussed in relation to assisted reproductive medicine. Third, we introduce the latest studies of animal experiments involving the ZP. Finally, immunocontraceptive vaccine development using various ZP antigens is reviewed.

High doses of medroxyprogesterone as the cause of disappearance of adherence of the zona pellucida to an oocyte

The zona pellucida (ZP) is an external glycoprotein membrane of oocytes of mammals and embryos in the early stage of their development. ZP first appears in growing ovarian follicles as an extracellular substance between the oocyte and granular cells. The zona pellucid markedly affects the development and maturation of the oocyte. The morphology of the ZP-oocyte complex allows a more precise determination of the oocyte maturity. According to numerous experimental studies, ZP is essential for preimplantation embryonic development of humans and other mammals. It prevents dispersion of blastomeres and enhances their mutual interactions. ZP is a dynamic structure responsible for the provision of nutrients to early forms of oocytes in mammals. The aim of the present study was untrastructural evaluation of the ZP-oocyte contact during inhibited ovulation. Female white rats (Wistar strain) received a suspension of medroxyprogesterone acetate (MPA) in incremental intramuscular bolus doses of 3.7 mg (therapeutic dose), 7.4 mg and 11.1 mg. The animals were decapitated 5 days after the administration of MPA. Ovarian sections were evaluated under a transmission electron microscope (TEM) Zeiss EM 900. Morphometric analysis of ZP was conducted using the cell imaging system by Olympus. In females exposed to therapeutic doses of MPA, ZP showed the structure of granular-fibrous reticulum of a medium electron density with single cytoplasmic processes originating from the surrounding structures. The oocyte cell membrane generated single, delicate processes directed toward ZP. Microvilli of the oocyte were short and thin. In the group receiving 7.4 mg of MPA, ZP had the structure of a delicate, loose granular-fibrous reticulum, and the oocyte cell membrane generated single microvilli directed toward ZP. In both those groups, the close ZP-oocyte contact was observed. Otherwise, in the group exposed to the highest MPA doses (11.1 mg), thicker and more numerous oocyte microvilli were found, which did not penetrate ZP matrix. They were dense, irregularly separated contour, forming a barrier between ZP and oocyte. The present findings are likely to suggest that MPA has inhibiting effects on the synthesis of binding proteins and causes the loss of the oocyte contact with ZP.

Estimating Young's modulus of zona pellucida by micropipette aspiration in combination with theoretical models of ovum

The zona pellucida (ZP) is the spherical layer that surrounds the mammalian oocyte. The physical hardness of this layer plays a crucial role in fertilization and is largely unknown because of the lack of appropriate measuring and modelling methods. The aim of this study is to measure the biomechanical properties of the ZP of human/mouse ovum and to test the hypothesis that Young's modulus of the ZP varies with fertilization. Young's moduli of ZP are determined before and after fertilization by using the micropipette aspiration technique, coupled with theoretical models of the oocyte as an elastic incompressible half-space (half-space model), an elastic compressible bilayer (layered model) or an elastic compressible shell (shell model). Comparison of the models shows that incorporation of the layered geometry of the ovum and the compressibility of the ZP in the layered and shell models may provide a means of more accurately characterizing ZP elasticity. Evaluation of results shows that although the results of the models are different, all confirm that the hardening of ZP will increase following fertilization. As can be seen, different choices of models and experimental parameters can affect the interpretation of experimental data and lead to differing mechanical properties.

Zona-free embryo culture: is it a viable option to improve pregnancy rates?

Sporadic reports published during the previous decade have documented pregnancies achieved with transfer of zona-free human embryos. Although the overall efficiency seems to be good and some authors have suggested systematic application for special infertility problems, there have been only a few attempts to compare the benefits of zona-free embryo culture and transfer with the traditional approach using zona-intact embryos. So far, the majority of instances in which zona-free culture has been applied have occurred accidentally. This review summarizes the known functions of the zona pellucida, analyses natural and artificial situations where its function is compromised, including zona hardening and difficult hatching that seem to be related to in-vitro embryo culture, and discusses possible methods and timing for artificial zona removal. With the availability of in-vitro systems capable of replacing important functions of the zona pellucida, routine use of zona-free culture for the whole in-vitro period, after or even before fertilization, is a realistic possibility with potential additional benefits. Based on the increasing amount of animal studies, a systematic comparison is suggested that may eventually diminish the handicaps of the in-vitro situation and lead to simplification of manipulations as well as higher success rates after embryo transfer.

Zona pellucida birefringence score and meiotic spindle visualization in relation to embryo development and ICSI outcomes

The meiotic spindle and the zona pellucida exhibit molecular order when imaged with polarized optics. This study aimed to investigate possible factors contributing to the zona pellucida birefringence score and meiotic spindle visualization, and to evaluate whether these structures may predict intracytoplasmic sperm injection outcomes. Oocytes were divided into groups according to zona pellucida birefringence and meiotic spindle visualization. In addition, the cycles were split into three groups based on the zona birefringence of transferred embryos. A positive correlation was observed between zona birefringence and meiotic spindle visualization. In addition, when the meiotic spindle was observed, the fertilization rate among oocytes with high or low zona pellucida birefringence was similar. Implantation and pregnancy rates were significantly higher when embryos derived from high birefringence oocytes were exclusively transferred (P = 0.041 and P = 0.004 respectively). Furthermore, the miscarriage rate was higher when embryos derived from low birefringence oocytes were exclusively transferred. On the other hand, the total dose of FSH negatively affected meiotic spindle visualization. Results show that selection of embryos based on zona pellucida and meiotic spindle imaging can significantly improve implantation and pregnancy rates. Moreover, the dose of FSH used for ovarian stimulation may affect the organization of the oocyte meiotic spindle.

Automatic user-independent zona pellucida imaging at the oocyte stage allows for the prediction of preimplantation development

OBJECTIVE

To analyze whether a change in three-dimensional structure of the zona pellucida could indicate suboptimal gamete quality.

DESIGN

Prospective study.

SETTING

Women's general hospital.

PATIENT(S)

A total of 72 patients who gave informed consent.

INTERVENTION(S)

The birefringence of all oocytes was prospectively analyzed with an automatic user-independent polarization microscopy imaging system.

MAIN OUTCOME MEASURE(S)

Birefringence of the inner zona layer, preimplantation development, implantation, and pregnancy.

RESULT(S)

In approximately one third of all gametes (244/712), the system's automatic detection of the inner zona layer did not succeed. This phenomenon was a negative predictor of compaction (P<0.01), blastulation (P<0.001), and pregnancy (P<0.001). In cases of successful zona imaging, the score based on the birefringence of the inner zona layer was a strong predictor of blastocyst formation but not of embryo quality or pregnancy (P>0.05). Interestingly, antagonist protocol resulted in lower zona scores as compared with the long protocol (P<0.05).

CONCLUSION(S)

Combining the information from both undetected and detected oocytes, zona imaging was a helpful tool in oocyte selection. This knowledge might further help to reduce both the time in culture and the number of concepti considered for transfer.

Incomplete denudation of oocytes prior to ICSI enhances embryo quality and blastocyst development

BACKGROUND

Granulosa cells are essential mediators of oocyte maturation and fertilization. Because of the denudation of oocytes in preparation for ICSI, any potential positive effect of surplus cumulus cells (CCs) on further development would be unable to exert further effect. In order to evaluate the actual influence of adhering cumulus cells on further preimplantation development, this prospective study was carried out.

METHODS

Sibling cumulus-oocyte complexes for 57 ICSI patients were split into a study group (incomplete denudation, n = 314) and a control group (complete denudation, n = 336). According to the cumulus cell pattern after partial denudation, mature gametes from the study group were further subdivided into type A oocytes, which showed several prominent CC clusters (n = 202), and type B (n = 75), which showed a more homogeneous pattern with CC covering the whole surface of the gamete.

RESULTS

In immature oocytes, presence of adhered CCs led to a significant increase in resumption of meiosis (P < 0.01). Fertilization rate (P < 0.05) and ability to cleave (P < 0.01) was impaired in the study group, because of difficulties in ICSI of type B oocytes. By contrast, embryo morphology on days 2 (P < 0.01) and 3 (P < 0.05), as well as blastocyst formation, was better (P < 0.05) in the study group (55 blastocysts out of 88 zygotes) as compared to that in the control group (49/105).

CONCLUSION

These data indicate that co-culture of oocytes with attached CCs may enhance preimplantation development.

Ultrastructural Dynamics of Human Reproduction, from Ovulation to Fertilization and Early Embryo Development1

This study describes the updated, fine structure of human gametes, the human fertilization process, and human embryos, mainly derived from assisted reproductive technology (ART). As clearly shown, the ultrastructure of human reproduction is a peculiar multistep process, which differs in part from that of other mammalian models, having some unique features. Particular attention has been devoted to the (1) sperm ultrastructure, likely "Tygerberg (Kruger) strict morphology criteria"; (2) mature oocyte, in which the MII spindle is barrel shaped, anastral, and lacking centrioles; (3) three-dimensional microarchitecture of the zona pellucida with its unique supramolecular filamentous organization; (4) sperm-egg interactions with the peculiarity of the sperm centrosome that activates the egg and organizes the sperm aster and mitotic spindles of the embryo; and (5) presence of viable cumulus cells whose metabolic activity is closely related to egg and embryo behavior in in vitro as well as in vivo conditions, in a sort of extraovarian "microfollicular unit." Even if the ultrastructural morphodynamic features of human fertilization are well understood, our knowledge about in vivo fertilization is still very limited and the complex sequence of in vivo biological steps involved in human reproduction is only partially reproduced in current ART procedures.

Possible applications of a non-contact 1.48 μm wavelength diode laser in assisted reproduction technologies

Recently, one laser system has been introduced in IVF fulfilling all safety requirements, while achieving a high standard of reproducibility in terms of ablation diameter. This 1.48 microm wavelength indium-gallium-arsenic-phosphorus (InGaAsP) semiconductor laser offers a variety of laser applications to the embryologist. On the one hand, zona pellucida of oocytes or embryos can be manipulated in order to facilitate ICSI or biopsy and assist hatching, and on the other, spermatozoa may be paralysed or immobilized prior to usage. To conclude, the 1.48 microm diode laser provides a promising tool for the microdissection of subcellular targets. The diode laser stands out due to the rapidity, the simplicity and the safety of the procedure which is supported by healthy offspring after laser application.

High magnitude of light retardation by the zona pellucida is associated with conception cycles

BACKGROUND

Failures in expression of zona proteins correlate to subfertility in animals. Low expression of the zona proteins by the growing human oocyte may indicate reduced developmental potential. Therefore, we non-invasively analysed the thickness and the structure of the zona pellucida (ZP) of human oocytes with respect to embryo fate after ICSI.

METHODS

Retardance magnitude and thickness of the inner, middle and outer layers of the ZP were quantitatively analysed by a Polscope in 166 oocytes selected for transfer after ICSI (63 patients; 32.8 +/- 4.4 years) on the basis of pronuclear score at day 1. Blastomere number was determined at day 2. Data were compared between conception cycles (CC; 65 oocytes/23 patients) and non-conception cycles (NCC; 101 oocytes/40 patients) and with respect to maternal age.

RESULTS

The thickness was slightly elevated (P < 0.001), and the mean magnitude of light retardance was nearly 30% higher (P < 0.001) in the inner layer of the zona pellucida of oocytes contributing to CC compared to NCC. Embryos in the CC group tended to develop faster.

CONCLUSIONS

The magnitude of light retardance by the zona pellucida inner layer appears to present a unique non-invasive marker for oocyte developmental potential.