Second polar body extrusion is highly predictive for oocyte fertilization as soon as 3 hr after intracytoplasmic sperm injection (ICSI)

Rescue intracytoplasmic sperm injection improved cumulative live birth rate for cycles with second polar body extrusion rate <50% in young women: generalized addictive model

OBJECTIVE

To determine the indications for early rescue intracytoplasmic sperm injection (ICSI) application.

DESIGN

A retrospective cohort study.

SETTING

A center for reproductive medicine.

PATIENT(S)

The study included 19,808 patients who underwent conventional in vitro fertilization (IVF) or rescue ICSI for their first cycles between February 2017 and December 2021.

INTERVENTION(S)

Rescue ICSI cycles constituted the study group, where oocytes that had not extruded the second polar body 4-6 hours after insemination were rescued by ICSI. The control group consisted of conventional IVF cycles with no interventions to rescue oocytes without the second polar body. Generalized additive models were constructed to describe the relationship between the second polar body extrusion rate and cumulative live birth rate in conventional IVF and rescue ICSI cycles, respectively. The cutoff value of the second polar body extrusion rate guiding rescue ICSI application was determined from the intersection point of generalized additive models. Maternal age range applicable to rescue ICSI was further analyzed using the same method. Clinical outcomes were compared between conventional IVF and rescue ICSI cycles across different second polar body extrusion rate and maternal age subgroups.

MAIN OUTCOME MEASURE(S)

The second polar body extrusion rate and maternal age range for rescue ICSI application, normal fertilization rate, and cumulative live birth rate.

RESULT(S)

Generalized additive models showed that the cutoff value for the second polar body extrusion rate about rescue ICSI application was 50%. When the rate <50%, normal fertilization rate and cumulative live birth rate (63.7% vs. 46.1%; odds ratio, 1.609; 95% confidence interval, 1.276-2.030) were significantly higher in rescue ICSI cycles than conventional IVF cycles. When the rate ≥50%, rescue ICSI cycles had similar normal fertilization rate and cumulative live birth rate compared with conventional IVF cycles. Further analysis on maternal age in cycles with second polar body extrusion rate <50% released that rescue ICSI cycles showed a higher cumulative live birth rate (67.7% vs. 48.3%; odds ratio, 1.732; 95% confidence interval, 1.361-2.202) than conventional IVF cycles for women aged <38 years.

CONCLUSION(S)

In vitro fertilization cycles with second polar body extrusion rate <50% in women aged <38 years was applicable to early rescue ICSI.

A quantitative analysis of stored frozen surplus embryos in the UK

The number of surplus frozen human embryos in storage in the United Kingdom (UK) is at its highest level since records began in 1991 and the formation of the UK Human Fertilisation and Embryology Authority (HFEA). This study features a quantitative analysis of data from 1991 to 2019 provided by the HFEA as well as a commentary on observed trends within this data. We also discuss trends relating to the final destiny of surplus embryos. Data analysis show that at least 130,000 stored embryos have been discarded in the UK since 1991, while another 500,000 embryos are currently being stored in a frozen state, of which a significant proportion is likely to be discarded in the future. However, this creates a moral dilemma since UK legislation relating to human embryos is based on the 1984 Warnock Report which recognizes that they have a special moral status.

Assisted oocyte activation effects on the morphokinetic pattern of derived embryos

OBJECTIVE

Assisted oocyte activation (AOA) can restore fertilization rates after IVF/ICSI cycles with fertilization failure. AOA is an experimental technique, and its downstream effects remain poorly characterized. Clarifying the relationship between AOA and embryo, morphokinetics could offer complementary insights into the quality and viability of the embryos obtained with this technique. The aim of this study is to compare the preimplantation morphokinetic development of embryos derived from ICSI-AOA (experimental group) vs. ICSI cycles (control group).

METHODS

A retrospective cohort study was carried out with 141 embryos from fresh oocyte donation cycles performed between 2013 and 2017; 41 embryos were derived from 7 ICSI-AOA cycles and 100 embryos from 18 ICSI cycles. Morphokinetic development of all embryos was followed using a time-lapse system.

RESULTS

We show that embryos from both groups develop similarly for most milestones, with the exception of the time of second polar body extrusion (tPB2) and the time to second cell division (t3).

CONCLUSIONS

We conclude that ionomycin mediated AOA does not seem to affect the morphokinetic pattern of preimplantation embryo development, despite the alterations found in tPB2 and t3, which could directly reflect the use of a Ca2+ ionophore as a transient and quick non-physiologic increase of free intracytoplasmic Ca2+.

Determining the need for rescue intracytoplasmic sperm injection in partial fertilisation failure during a conventional IVF cycle

To explore the need for rescue intracytoplasmic sperm injection (ICSI) in cases of partial fertilisation failure during a conventional in vitro fertilisation cycle, rescue ICSI was performed for cycles with a fertilisation rate of <50%. The data were divided into three groups based on the fertilisation rate: group 1 (0%), group 2 (<25%) and group 3 (>25%). The impact of rescue ICSI on each group was then analysed in terms of ovum fertilisation, embryo development, embryo utilisation and selection of embryos for transfer. Rescue ICSI was performed on 1831 unfertilised oocytes from 313 cycles. The fertilisation rates for group 1, group 2 and group 3 were 74.66, 68.35 and 65.46%, and the rate of polyploidy in the three groups was 8.55, 11.33, and 14.47%. The percentage of embryos that can be transferred from rescue ICSI for group 2 was 38.33%, and this value was higher than those of the other two groups. It is concluded that rescue ICSI is not recommended for patients with an IVF rate of >25% as the procedure is associated with a greater risk and low returns. However, it is feasible to perform rescue ICSI for patients with IVF rates of <25%.

Time-lapse videography of human oocytes following intracytoplasmic sperm injection: events up to the first cleavage division

A total of 341 fertilized and 37 unfertilized oocytes from 63 intracytoplasmic sperm injection (ICSI) treatment cycles were included for retrospective assessment using the Embryoscope time-lapse video system. The second polar body (pb2) extrusion occurred at 2.9±0.1 h (range 0.70-10.15 h) relative to sperm injection. All oocytes reduced in size following sperm injection (p<0.05) with shrinkage ceasing after 2h in the unfertilized and at pb2 extrusion in the fertilized oocytes. Pb2 extrusion was significantly delayed for women aged >38 years compared to those <35 years (3.4±0.2 vs. 2.8±0.1, p<0.01) or 35-38 years (3.4±0.2 vs. 2.8±0.1, p<0.01), but timing was not related to the Day 3 morphological grades (1-4) of subsequent embryos (2.9±0.1, 2.9±0.1, 2.8±0.2 and 3.0±0.1; p>0.05 respectively). A shorter time of first cleavage division relative to either sperm injection or pb2 extrusion is associated with both top grade (AUC=0.596 or 0.601, p=0.006 or 0.004) and usable embryos (AUC=0.638 or 0.632, p=0.000 respectively) on Day 3. In summary, (i) pb2 of human oocytes extrudes at various times following sperm injection, (ii) the timing of pb2 extrusion is significantly delayed when female age >38 years, but not related to subsequent embryo development, (iii) all human oocytes reduce in size following sperm injection, (iv) completion of pb2 extrusion in the fertilized oocytes is a pivotal event in terminating shrinkage of the vitellus, and (v) time to first cleavage division either from sperm injection or pb2 extrusion is a significant predictive marker for embryo quality on Day 3.

The value of second polar body detection 4 hours after insemination and early rescue ICSI in preventing complete fertilisation failure in patients with borderline semen

In this study we evaluated the value of short-time insemination and early rescue intra-cytoplasmic sperm injection (ICSI) in preventing the occurrence of complete fertilisation failure for mild or moderate male infertility patients. A total of 866 couples with borderline semen who underwent in vitro fertilisation treatment in 2010 were included. Regular insemination was performed between January and June of 2010 and short-term insemination was performed from July through December 2010, where, as early as 4h after insemination, oocytes were denuded from cumulus cells and extrusion of the second polar body was evaluated. Of the 4153 mature oocytes with a detectable second polar body 4 h after insemination, 3874 (93.3%) showed signs of fertilisation on Day 1. Where no second polar body was present in any of the retrieved oocytes for a given patient, rescue ICSI was performed immediately. Similar rates of normal fertilisation and percentage of good-quality embryos were obtained between early rescue ICSI and regular ICSI. Clinical pregnancy occurred in 16 of 43 patients (37.2%) receiving early rescue ICSI. Our results showed early rescue ICSI in combination with evaluation of the second polar body 4 h following insemination is an effective method to prevent complete fertilisation failure for patients with mild or moderate male infertility.

Kinetics of pronuclear development and the effects of vector type and timing of injection on the efficiency of gene transfer into rhesus macaque embryos

A series of experiments was performed to determine the dynamics of pronuclear development as well as the efficiency of either adenovirus-associated (AAV) or lentivirus-derived vectors to introduce a green fluorescent protein (GFP) reporter gene into rhesus macaque (Macaca mulatta) embryos. Assessment of pronuclear development at various times after fertilization revealed that the appearance of pronuclei was determined by the presence of the first and the timing of the second polar body. The dynamics of pronuclear formation was a significant determinant of whether an oocyte reached the blastocyst stage, however, when the percentage of blastocysts were based on the number of zygotes, the timing of the appearance of polar bodies did not appear to have any effect on subsequent development. Injection of different AAV-derived vectors showed that the serotype of the vector did not affect development or the proportion of transgenic embryos. Moreover, all putative transgenic embryos proved to be expression mosaics. Injection of embryos with lentiviral vectors showed that timing of injection (before or after fertilization) had no effect on subsequent transgene expression, but that the type of reporter gene determined post-injection development and rate of transgenesis. The transfer of embryos following injection of a lentiviral vector into three recipients resulted in one pregnancy which was lost during the second trimester. Analysis of fetal tissues showed ubiquitous presence of the transgene and GFP expression in all tissues examined. These results show that lentivirus-derived vectors can efficiently transform rhesus embryos and are suitable for the generation of transgenic rhesus monkeys.

Duplication of the sperm genome by human androgenetic embryo production: towards testing the paternal genome prior to fertilization

There is currently no technique for evaluating the sperm genome before fertilization. However, sperm genome duplication could offer a way forward, whereby one of the sister blastomeres of a 2-cell haploid androgenetic embryo could be analysed. A method was developed for production of human androgenotes by enucleation of oocytes at telophase II (TII) after intracellular sperm injection (ICSI). The results were compared with those obtained via the more usual procedure of oocyte enucleation at metaphase II (MII) prior to ICSI. TII enucleation led to an improvement in the rate of embryo survival, increased the production rate of 1PN-embryos, and also the production of 2- to 8-cell-stage embryos (85.0, 74.9 and 65.8% in TII enucleation, versus 73.8, 48.9 and 33.3% in MII enucleation). Fluorescence in-situ hybridization (FISH) analysis of 30 2- to 5-cell androgenic embryos for two to seven chromosomes revealed the correct chromosome distribution in 76.7% of haploid human androgenotes.

Amino acids promote human blastocyst development in vitro

Supplementation of culture media with amino acids has been shown to benefit preimplantation embryo development in several species. This randomized study analysed the in-vitro development of human embryos obtained after IVF in the presence or absence of a combination of amino acids from the 2- to 4-cell stage to the blastocyst stage. A total of 129 human embryos was randomly distributed between three serum-free chemically defined sequential media: (i) glucose-free Earle's balanced salt solution (EBSS) with glutamine (Gln) prior to morula stage, supplemented with glucose for blastocyst formation; (ii) glucose-free EBSS with glutamine and non-essential amino acids (AA) for cleavage stage development, and supplemented with all 20 AA for blastocyst formation (Earle's+AA); and (iii) a sequential commercial medium containing amino acids (K-SCIM). Embryos were individually cultured for successive periods of 24 h. On day 6 of development, blastocysts were differentially labelled and the numbers of trophectoderm and inner cell mass cells, mitoses and dead cells were examined. Blastocyst development was similar for the three sequential media. The mixture of AA significantly increased total blastocyst cell numbers from 61.8 +/- 4.2 with Earle's+Gln to 99.3 +/- 8.4 with Earle's+AA and 100.2 +/- 9.4 with K-SCIM (P = 0.005). This increase was present in both the trophectoderm and inner cell mass lineages (P < 0.02). Furthermore, the dead cell index was significantly lower with Earle's+AA (P = 0.047).

Noninvasive assessment of glucose and pyruvate uptake by human embryos after intracytoplasmic sperm injection and during the formation of pronuclei

OBJECTIVE

To improve in vitro culture conditions and human embryo selection before transfer after IVF with intracytoplasmic sperm injection (ICSI).

DESIGN

A controlled, randomized, prospective study.

SETTING

University hospital-based IVF-ET program.

PATIENT(S)

Couples undergoing ICSI.

INTERVENTION(S)

Culture of human embryos in the presence of 1 mM or 5.56 mM glucose and metabolic measurements with the use of noninvasive microfluorescence assays immediately after ICSI to the time of transfer.

MAIN OUTCOME MEASURE(S)

Embryo development, implantation rate, and glucose and pyruvate uptake.

RESULT(S)

Fertilization rates, early embryo development, and implantation rates were not significantly different between 1 mM and 5.56 mM glucose. Pyruvate uptake was significantly higher during the formation of the pronuclei, at 15 +/- 0.7 and 11.4 +/- 1.3 pmol/embryo/h for fertilized and unfertilized oocytes, respectively. Pyruvate uptake did not correlate with cleavage stage or embryo morphology. However, during the second day of incubation, pyruvate uptake was significantly higher for the untransferred embryos of pregnant women compared with nonpregnant women, at 17.9 +/- 1.5 and 10.8 +/- 1.0 pmol/embryo/h, respectively.

CONCLUSION(S)

The increased level of pyruvate uptake during fertilization reflects the increased demand for energy necessary for the formation of the pronuclei. However, the metabolic measurements could not improve the selection of embryos with the best implantation potential. Finally, the reduction of glucose concentration in the culture medium failed to improve embryo viability.

Sperm deposition site during ICSI affects fertilization and development

OBJECTIVE

To evaluate the effects of sperm placement during ICSI relative to the M-II spindle location on fertilization and preimplantation development.

DESIGN

Retrospective analysis of oocyte fertilization and embryo development with respect to sperm deposition site during ICSI.

SETTING

A program of IVF-ET.

PATIENT(S)

Seven hundred seventy-six patients.

INTERVENTION(S)

Egg quality, sperm deposition site, and polar-body position were recorded during ICSI; fertilization was assessed on day 1; embryo development was evaluated on days 2 and 3.

MAIN OUTCOME MEASURE(S)

Fertilization, embryo development, and implantation rates.

RESULT(S)

Normal fertilization is not affected by polar-body orientation, with the exception of a significantly lower fertilization rate from a 9 o'clock polar-body orientation. Injections with the polar-body positioned at 7 or 11 o'clock result in the greatest number of high-quality embryos, significantly more than the adjacent 6 or 12 o'clock polar-body orientations and irrespective of oocyte anomaly frequency. Embryos originating from the 7 or 11 o'clock polar-body category implant at a higher rate, although the data are not significant.

CONCLUSION(S)

The placement of the sperm during ICSI relative to the presumed location of the meiotic spindle significantly impacts fertilization and high-quality embryo development. Sperm deposition in the M-II spindle area should be avoided. It appears that development, and not fertilization, is improved by decreasing the distance between the sperm cell and the spindle.

Selection of good embryos for transfer depends on embryo cohort size: implications for the 'mild ovarian stimulation' debate

Embryo quality evaluated by the embryo morphology is a critical parameter in human in-vitro fertilization (IVF) and embryo transfer. It determines which and how many embryos will be replaced, as pregnancy rates are directly related to number and quality of transferred embryos. This retrospective analysis included 1301 IVF and embryo transfer cycles to identify which factors influenced embryo quality. Embryo quality did not correlate with maternal age, causes of infertility, ovarian stimulation parameters or embryo cohort size. However, the mean score of transferred embryos was significantly higher for patients with more than five embryos compared to fewer than five embryos (P < 0.001), irrespective of maternal age. Patients tended to produce a similar embryo quality from cycle to cycle, r = 0.33 (P < 0.001) for the embryo cohort and r= 0.47 (P < 0.001) for the transferred embryos. Poor embryo morphology probably reflects oocytes with compromised development competence and could be an independent factor of infertility. Furthermore, a large embryo cohort was the main factor increasing the chances of at least one good embryo in the cohort.