Prediction of nuclear maturity from cumulus-coronal morphology: influence of embryologist experience

Gonadotropin elevation is ootoxic to ovulatory oocytes and inhibits oocyte maturation, and activin decoy receptor ActRIIB:Fc therapeutically restores maturation

BACKGROUND

Elevated FSH often occurs in women of advanced maternal age (AMA, age ≥ 35) and in infertility patients undergoing controlled ovarian stimulation (COS). There is controversy on whether high endogenous FSH contributes to infertility and whether high exogenous FSH adversely impacts patient pregnancy rates.

METHODS

The senescence-accelerated mouse-prone-8 (SAMP8) model of female reproductive aging was employed to assess the separate impacts of age and high FSH activity on the percentages (%) of viable and mature ovulated oocytes recovered after gonadotropin treatment. Young and midlife mice were treated with the FSH analog equine chorionic gonadotropin (eCG) to model both endogenous FSH elevation and exogenous FSH elevation. Previously we showed the activin inhibitor ActRIIB:Fc increases oocyte quality by preventing chromosome and spindle misalignments. Therefore, ActRIIB:Fc treatment was performed in an effort to increase % oocyte viability and % oocyte maturation.

RESULTS

The high FSH activity of eCG is ootoxic to ovulatory oocytes, with greater decreases in % viable oocytes in midlife than young mice. High FSH activity of eCG potently inhibits oocyte maturation, decreasing the % of mature oocytes to similar degrees in young and midlife mice. ActRIIB:Fc treatment does not prevent eCG ootoxicity, but it restores most oocyte maturation impeded by eCG.

CONCLUSIONS

FSH ootoxicity to ovulatory oocytes and FSH maturation inhibition pose a paradox given the well-known pro-growth and pro-maturation activities of FSH in the earlier stages of oocyte growth. We propose the FOOT Hypothesis ("FSH OoToxicity Hypothesis), that FSH ootoxicity to ovulatory oocytes comprises a new driver of infertility and low pregnancy success rates in DOR women attempting spontaneous pregnancy and in COS/IUI patients, especially AMA women. We speculate that endogenous FSH elevation also contributes to reduced fecundity in these DOR and COS/IUI patients. Restoration of oocyte maturation by ActRIB:Fc suggests that activin suppresses oocyte maturation in vivo. This contrasts with prior studies showing activin A promotes oocyte maturation in vitro. Improved oocyte maturation with agents that decrease endogenous activin activity with high specificity may have therapeutic benefit for COS/IVF patients, COS/IUI patients, and DOR patients attempting spontaneous pregnancies.

Maternal age and gonadotrophin elevation cooperatively decrease viable ovulated oocytes and increase ootoxicity, chromosome-, and spindle-misalignments: '2-Hit' and 'FSH-OoToxicity' mechanisms as new reproductive aging hypotheses

While there is consensus that advanced maternal age (AMA) reduces oocyte yield and quality, the notion that high FSH reduces oocyte quality and causes aneuploidy remains controversial, perhaps due to difficulties controlling the confounding variables of age and FSH levels. Here, contributions of age and gonadotrophin elevation were separately controlled using a mouse model of human female reproductive aging. Ovulated oocytes were collected from young and midlife mice after 0-, 2.6-, or 17-day treatment with the FSH analog equine chorionic gonadotrophin (eCG), to model both exogenous FSH elevation within a single treatment cycle (as in controlled ovarian stimulation (COS)), and chronic endogenous FSH elevation during multiple cycles (as in diminished ovarian reserve). After 17-day eCG, fewer total oocytes/mouse are ovulated in midlife than young mice, and a precipitous decline in viable oocytes/mouse is observed in midlife but not young mice throughout eCG treatment. eCG is potently ootoxic to ovulatory oocytes and strongly induces chromosome- and spindle-misalignments within 2.6 days of eCG in midlife, but only after 17 days in young mice. These data indicate that AMA increases susceptibility to multiple adverse effects of elevated FSH activity in ovulated oocytes, including declines in total and viable oocytes/mouse, and induction of ootoxicity and aneuploidy. Two hypotheses are proposed for underlying causes of infertility in women. The FSH OOToxicity Hypothesis ('FOOT Hypothesis') posits that high FSH is ootoxic to ovulatory oocytes and that FSH ootoxicity is a root cause of low pregnancy success rates in naturally cycling women with high FSH and IUI patients undergoing COS. The '2-Hit Hypothesis' posits that AMA increases susceptibility to FSH-induced ootoxicity and aneuploidy.

Low oocyte maturity ratio is associated with a reduced in vitro fertilization and intracytoplasmic sperm injection live birth rate

OBJECTIVE

To determine whether a low oocyte maturity ratio in a cohort of oocytes from an in vitro fertilization cycle predicts outcomes and to examine clinical factors associated with oocyte maturity.

DESIGN

A retrospective cohort study.

SETTING

An academic medical center.

INTERVENTION(S)

Determination of oocyte maturity immediately after the retrieval and 6 hours later if intracytoplasmic sperm injection was performed.

MAIN OUTCOME MEASURE(S)

The primary outcome was live birth rate after the first embryo transfer. Secondary outcomes included clinical pregnancy, miscarriage, and fertilization rates.

RESULT(S)

After adjusting for age, preimplantation genetic testing, and number of embryos transferred, we found that a low oocyte maturity ratio was associated with a decreased live birth rate (adjusted odds ratio [AOR], 0.41; 95% confidence interval [CI], 0.22-0.77) and clinical pregnancy rate (AOR, 0.32; 95% CI, 0.17-0.61). We did not find a relationship between oocyte maturity and miscarriage rate (AOR, 0.25; 95% CI, 0.03-1.91) or fertilization rate (Welch test). The number of 2 pronuclei embryos per retrieved oocyte was found to be associated with the maturity ratio at retrieval. Patients with anovulation had slightly reduced oocyte maturity compared with other diagnostic groups.

CONCLUSION(S)

Low oocyte maturity ratio is an important factor related to poor in vitro fertilization outcomes, including decreased pregnancy and live birth rates.

Oocyte quality and embryo selection strategies: a review for the embryologists, by the embryologists

With the advance of assisted reproduction techniques, and the trend towards blastocyst culture and single embryo transfer, gamete and embryo assessment have gained greater importance in ART treatment. Embryo quality depends mainly on gamete quality and culture conditions. Oocyte maturity identification is necessary in order to plan fertilization timing. Mature oocytes at the metaphase II stage show a higher fertilization rate compared to immature oocytes. Morphology assessment is a critical yet challenging task that may serve as a good prognostic tool for future development and implantation potential if done effectively. Various grading systems have been suggested to assess embryos at pronuclear, cleavage, and blastocyst stages. By identifying the embryo with the highest implantation potential, it is possible to reduce the number of embryos transferred without compromising the chances of a successful pregnancy. Apart from the conventional morphology assessment, there are several invasive or non-invasive methods for embryo selection such as preimplantation genetic testing, morphokinetics, proteomics, metabolomics, oxygen consumption, and measurement of oxidative stress in culture medium. Morphokinetics is a method based on time-lapse technology and continuous monitoring of embryos. In this review, we aim to describe and compare the most effective and widely used methods for gamete and embryo assessment as well as embryo selection.

Shortened estrous cycle length, increased FSH levels, FSH variance, oocyte spindle aberrations, and early declining fertility in aging senescence-accelerated mouse prone-8 (SAMP8) mice: concomitant characteristics of human midlife female reproductive aging

Women experience a series of specific transitions in their reproductive function with age. Shortening of the menstrual cycle begins in the mid to late 30s and is regarded as the first sign of reproductive aging. Other early changes include elevation and increased variance of serum FSH levels, increased incidences of oocyte spindle aberrations and aneuploidy, and declining fertility. The goal of this study was to investigate whether the mouse strain senescence-accelerated mouse-prone-8 (SAMP8) is a suitable model for the study of these midlife reproductive aging characteristics. Midlife SAMP8 mice aged 6.5-7.85 months (midlife SAMP8) exhibited shortened estrous cycles compared with SAMP8 mice aged 2-3 months (young SAMP8, P = .0040). Midlife SAMP8 mice had high FSH levels compared with young SAMP8 mice, and mice with a single day of high FSH exhibited statistically elevated FSH throughout the cycle, ranging from 1.8- to 3.6-fold elevation on the days of proestrus, estrus, metestrus, and diestrus (P < .05). Midlife SAMP8 mice displayed more variance in FSH than young SAMP8 mice (P = .01). Midlife SAMP8 ovulated fewer oocytes (P = .0155). SAMP8 oocytes stained with fluorescently labeled antitubulin antibodies and scored in fluorescence microscopy exhibited increased incidence of meiotic spindle aberrations with age, from 2/126 (1.59%) in young SAMP8 to 38/139 (27.3%) in midlife SAMP8 (17.2-fold increase, P < .0001). Finally, SAMP8 exhibited declining fertility from 8.9 pups/litter in young SAMP8 to 3.5 pups/litter in midlife SAMP8 mice (P < .0001). The age at which these changes occur is younger than for most mouse strains, and their simultaneous occurrence within a single strain has not been described previously. We propose that SAMP8 mice are a model of midlife human female reproductive aging.

Assisting in vitro fertilization by manipulating cumulus-oocyte-complexes either mechanically or enzymatically does not prevent IVF failure

OBJECTIVE

This prospective study was set up in order to analyze whether additional treatment (cutting off supernumerous cumulus cells; adding hyaluronidase) of the cumulus-oocyte-complex (COC) would help to improve treatment outcome.

MATERIAL AND METHODS

COCs from 50 patients were prospectively subdivided into a control group A (no manipulation of COC) and two study groups. In group B, surplus cumulus cells were cut off using syringes, and in the second study group COCs were incubated with a 1:11 dilution of hyaluronidase (final concentration 7 IU/l). Main outcome measures were fertilization rate, embryo development, as well as rates of implantation, pregnancy, and live birth.

RESULTS

Fertilization was higher in group C as compared to the untreated control group A (p<0.05). However, complete fertilization failure could not be avoided by any of the modified IVF approaches. Compaction on day 4 and blastocyst quality on day 5 were significantly improved in group C as compared to group B (but not to group A). Rates of implantation, pregnancy, and live birth were not affected by any of the methods.

CONCLUSION

ICSI seems to be the only choice for avoiding the vast majority of fertilization failures after IVF.

Serum antimüllerian hormone concentrations on day 3 of the in vitro fertilization stimulation cycle are predictive of the fertilization, implantation, and pregnancy in polycystic ovary syndrome patients undergoing assisted reproduction

OBJECTIVE

To determine the possible relationship between serum antimüllerian hormone (AMH) concentrations on day 3 and controlled ovarian stimulation and reproductive outcomes in women with polycystic ovary syndrome.

DESIGN

Prospective, clinical trial.

SETTING

University hospital.

PATIENT(S)

Sixty women with PCOS.

INTERVENTION(S)

Serum concentrations of AMH measured on cycle day 3.

MAIN OUTCOME MEASURE(S)

Clinic pregnancy rate (CPR), implantation rate (IR), and fertilization rate (FR).

RESULT(S)

The CPR, IR, and FR were markedly different among the day-3 serum AMH groups (low, moderate, and high AMH groups). The CPR were 33.3, 46.1, and 60.0, respectively, in the low, moderate, and high serum AMH groups on day 3. The embryo IR were 18.6, 26.7, and 36.3, respectively. The FR were 54, 68, and 79, respectively. An AMH level≥3.01 ng/mL was shown to predict FR with a sensitivity of 86.4% and specificity of 75%. An AMH level≥3.2 ng/mL was shown to predict IR and CPR with sensitivity and specificity of 72.1% and 72.7%, and 75.6% and 77.3%, respectively.

CONCLUSION(S)

On day 3 of the in vitro fertilization stimulation cycle, serum concentrations of AMH can be used as a marker for ovarian response as well as reproductive outcome in assisted reproductive cycles of PCOS patients.

Blood clots in the cumulus-oocyte complex predict poor oocyte quality and post-fertilization development

Assessment of oocyte maturity and quality (morphological appearance) at the time of retrieval is difficult as the egg is obscured by a large cumulus mass that hinders adequate scoring. Since no data are available on the possible relationship between the cumulus-oocyte complex (COC) and oocyte morphology, this prospective intracytoplasmic sperm injection study was set up in 87 consecutive patients. COC were grouped according to expansion of both corona radiata and cumulus matrix. Special emphasis was placed on recording morphological anomalies of COC (inclusion of blood clots and amorphous clumps). For all mature ovae, quality was assessed and preimplantation development followed up to blastocyst stage if fertilized. The risk of not harvesting an oocyte was higher in COC with blood clots compared with normal cumulus matrices (P = 0.004). COC expansion did not allow for prediction of either nuclear status or quality of the egg. The presence of blood clots within the cumulus matrix was associated with reduced oocyte quality (dense central granulation), fertilization rate and blastocyst formation, compared with unaffected COC (P < 0.05). It may be postulated that COC showing blood inclusions derive from poor quality follicles, which has a detrimental effect on oocyte quality and further cleavage to blastocyst stage. Consequently, mechanical removal of blood clots cannot rescue the corresponding embryo.

Secretory mechanisms and Ca2+ signaling in gametes: similarities to regulated neuroendocrine secretion in somatic cells and involvement in emerging pathologies

Recent studies demonstrate that regulated secretion in probably all mammalian cells, from gonadotropes to gametes, utilizes similar signaling systems, intracellular Ca(2+) regulation, Ca(2+)-dependent proteins, cytoskeletal participation, and SNARE-mediated fusion. Thus, highly specialized cells, like sperm and eggs, should no longer be considered to have evolved a cell-type specific secretory mechanism. In gametes, Ca(2+)-dependent proteins and enzymes transduce elevations of intracellular Ca(2+) into secretory events, i.e., exocytosis of the acrosome in sperm and cortical granules in the egg. Just as secretory deficiencies have clinical consequences in endocrine and exocrine cells, failure of secretion of cortical granules or the acrosome can result in failure of normal fertilization or fertilization followed by abnormal development. With the advent of human in vitro fertilization, such gamete pathologies have been recently identified and have led to new clinical procedures to achieve normal fertilization and pregnancies. A better understanding of the common Ca(2+)-dependent secretory pathways in both gametes and somatic cells should be beneficial to investigating mis-regulation in either cell type.

Effect of oocyte morphology on embryo development and implantation

Assessment of oocyte morphology is a difficult task, since underlying mechanisms that change the appearance of the oocyte are multifactorial and complex. Significant morphological variations are known to exist among oocytes that may affect the developmental competence and implantation potential of the derived embryo. Morphological variations of the oocyte may result from intrinsic factors such as age and genetic defects or extrinsic factors such as stimulation protocols, culture conditions, and nutrition. The effect of these morphological variations of the oocyte on embryo development and implantation, however, is not conclusively defined because of methodological flaws inherent to most of the studies in the literature. This review will mainly discuss morphological markers of oocyte quality/viability in relation to the oocyte morphology and attempt to clarify whether morphological evaluation of the oocyte can be utilized for predicting the implantation potential of the derived embryo.

In vitro maturation, fertilization, and development of human germinal vesicle oocytes collected from stimulated cycles

OBJECTIVE

To evaluate whether germinal vesicle (GV) oocytes from stimulated cycles can be a source of embryos.

DESIGN

In vitro model study.

SETTING

Specialized laboratory of women's clinic.

PATIENT(S)

Women in whom oocytes were retrieved at the GV stage.

INTERVENTION(S)

After culture of GV oocytes in the modified TLP medium with human follicular fluid, oocytes that reached the metaphase II stage underwent ICSI. Potential of fertilization and subsequent cleavage of in vitro-matured oocytes was compared with that of an in vivo-matured control.

MAIN OUTCOME MEASURE(S)

Maturation rate, rate of pronuclei formation, and developmental activity.

RESULT(S)

The maturation rate of GV oocytes from follicles primed with gonadotropin was not affected by the presence or absence of cumulus. However, the maturation was more synchronous in oocytes with cumulus than in those without cumulus. Proportions of oocytes with two pronuclei and embryos cleaved to the 16-cell stage after ICSI were significantly lower in the oocytes matured in vitro than in the oocytes matured in vivo.

CONCLUSION(S)

Human GV oocytes from stimulated ovaries can be matured, fertilized, and developed in vitro. Production of embryos from GV oocytes will increase the opportunity for achieving pregnancy.

Biochemical and cellular insights into the temporal window of normal fertilization

Normal development depends on both the timing of fertilization and gamete quality, especially in assisted reproductive procedures. Recent studies of the proteins involved in the polyspermy block and cell cycle progression provide a cellular and biochemical basis for the short fertilizable lifespan of the mammalian egg in several species. Specifically, the status of cortical granules, zona proteins, cell cycle kinases, and intracellular calcium stores form a powerful panel of assays to monitor egg activation competence in eggs undergoing maturation and spontaneous activation events in mature eggs. An understanding of how these indicators are influenced by in vitro conditions and exogenous follicular stimulation should provide useful information for optimizing assisted reproductive procedures.

The correlation between follicular measurements, oocyte morphology, and fertilization rates in an in vitro fertilization program

OBJECTIVE

To explore the relationship between follicle size and the morphology of the oocyte-cumulus-corona complex with fertilization rates in stimulated cycles of IVF.

DESIGN

Retrospective comparison of measurements and observations of 2,429 oocytes from 215 patients undergoing 324 stimulated IVF cycles.

SETTING

A large hospital-based IVF program.

MAIN OUTCOME MEASURES

Individual follicles were measured by ultrasound before transvaginal aspiration and the size was recorded. The oocyte-cumulus-corona complex from each follicle was examined and classified. The oocytes were checked for evidence of fertilization 17 to 22 hours after insemination.

RESULTS

The fertilization rate of all oocytes regardless of morphological type revealed a positive linear correlation with increasing follicle diameter. The fertilization rates of type I oocytes was marginally higher than type II oocytes, controlling for follicle diameter; however, this difference did not achieve statistical significance. Oocytes from follicles with a mean diameter > or = 16 mm had significantly higher fertilization rates than did oocytes from follicles with a mean diameter < or = 14 mm.

CONCLUSIONS

Follicle size is a better predictor of fertilization than is morphological characterization of the oocyte-cumulus-corona complex in IVF.

Oocyte nuclear maturation at the time of oocyte aspiration is independent of in vitro fertilization potential in the domestic cat

This study determined (1) the temporal kinetics of nuclear maturation at and after follicular oocyte aspiration and (2) the significance of variations in nuclear maturation and sperm-oocyte co-incubation interval on in vitro fertilization (IVF) in the domestic cat. Female cats were treated with pregnant mares' serum gonadotropin followed 84 h later with human chorionic gonadotropin (hCG). Twenty-five hours after hCG, ovarian follicular oocytes were aspirated laparoscopically and classified according to morphological criteria. Oocytes classified as mature were cultured for 0, 2, 4, 6, or 8 h in Ham's F10 medium and then stained for nuclear maturation. The proportion of oocytes at metaphase II was similar (P > 0.05) at 0 (38.2%) and 2 (48.5%) h of culture, but was higher (P < 0.05) at 4 (76.5%), 6 (82.8%), and 8 (92.3%) h. Oocytes also were collected and cultured as described above and then co-incubated for 2 or 18 h with 5 x 10(5) motile cat sperm cells/ml. The incidence of IVF (cleavage to 2-cells by 30 h post-insemination) was consistently 2-fold higher (P > 0.05) for the 18 h compared to the 2 h gamete co-incubation groups. However, despite differences in nuclear maturation at the time of oocyte recovery, IVF success was unaffected (P > 0.05) by pre-insemination culture interval (0 h, 72.7%; 2 h, 73.3%; 4 h, 70.7%; 6 h, 57.8%; 8 h, 62.5%; 18 h group). Thus, the majority of oocytes recovered from cats treated with this gonadotropin regimen has not achieved metaphase II by follicular aspiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Maturational asynchrony between oocyte cumulus-coronal morphology and nuclear maturity in gonadotropin-releasing hormone agonist stimulations

OBJECTIVE

To determine oocyte meiotic maturity and asynchrony between cumulus-coronal morphology and nuclear maturity after gonadotropin-releasing hormone agonist (GnRH-a) and norethindrone-programmed stimulations.

DESIGN

Oocyte meiotic maturity was evaluated at follicular aspiration in 4,961 oocytes after GnRH-a/follicle-stimulating hormone (FSH)/human menopausal gonadotropin stimulations (hMG) for in vitro fertilization patients and 299 oocytes after norethindrone-programmed clomiphene citrate (CC)/hMG in oocyte donors. Maturational asynchrony between the oocyte's cumulus-coronal morphology and nuclear maturity was evaluated in 2,336 oocytes.

SETTING

In vitro fertilization program at the University of Iowa Hospitals and Clinics; academic tertiary care center.

INTERVENTIONS

After evaluating oocyte cumulus-coronal maturity, cumulus masses were spread to determine oocyte nuclear maturity.

RESULTS

Fourteen percent, 17%, 50%, 17%, and 2% of oocytes were prophase I, metaphase I, metaphase II, postmature metaphase II, and atretic, respectively. Asynchrony was noted in 28% of prophase I, 71% of metaphase I, 11% of metaphase II, 45% of postmature metaphase II, 32% of atretic, and 28% of all oocytes. Significant differences were not found between GnRH-a and norethindrone-programmed stimulations in asynchrony between cumulus-coronal morphology and nuclear maturity or percentage of prophase I, metaphase I, metaphase II, postmature metaphase II, or atretic oocytes. Sixty-seven percent of oocytes possessed a polar body at retrieval. The rate of fertilization was significantly higher for metaphase II oocytes than postmature metaphase II and metaphase I oocytes > prophase I oocytes. Parthenogenetic activation tended to be highest for postmature metaphase II oocytes. Embryo cleavage was significantly higher for postmature metaphase II, metaphase II, and metaphase I oocytes than for prophase I oocytes.

CONCLUSIONS

This is the first report of asynchrony between cumulus-coronal morphology and nuclear maturity at follicular aspiration in GnRH-a and norethindrone-programmed stimulations. Asynchrony was observed in 28% of oocytes. A higher percentage of oocytes possessed a polar body at egg retrieval with these stimulation regimens compared with rates reported previously for FSH, FSH/hMG, and CC/hMG stimulations.