of Oocyte Morphology on ICSI Outcomes

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© Springer Nature Switzerland AG 2020
A. Malvasi, D. Baldini (eds.)Pick Up and Oocyte Managementdoi.org/10.1007/978-3-030-28741-2_16



16. Relevance of Oocyte Morphology on ICSI Outcomes



Claire O’Neill1  , Stephanie Cheung1, Alessandra Parrella1, Derek Keating1, Philip Xie1, Zev Rosenwaks1   and Gianpiero D. Palermo1  


(1)
The Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medicine, New York, NY, USA

 



 

Claire O’Neill


 

Zev Rosenwaks



 

Gianpiero D. Palermo (Corresponding author)




Keywords

Oocyte morphologyICSIEmbryo implantationClinical outcome


The observation of the oocyte has always been at the base of the embryological evaluation since the inception of in vitro insemination procedures [1]. However, the identification of oocyte characteristics and/or ooplasm dysmorphism under an inverted microscope (Fig. 16.1) have mostly been carried out after the exposure of the oocyte-cumulus complex to the inseminating spermatozoa. Therefore, the evaluation of oocyte complexion was carried out mostly on oocytes that had failed to undergo fertilization. This led to the work of some investigators who attempted to describe these anomalies and concluded that dysmorphic oocytes were not capable of undergoing fertilization and if ever they would, they would not be able to develop into viable embryos [2].

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Fig. 16.1

Identification of oocyte characteristics and/or ooplasm dysmorphism under an inverted microscope


The advent of ICSI requiring removal of the cumulus cells (Fig. 16.2) has changed this assessment and has allowed embryologists to characterize oocyte morphology prior to sperm injection and therefore define specific morphological patterns mainly in terms of oocyte shape, nuclear attributes, cytoplasmic traits, and the zona pellucida features [3]. These patterns appear as a consequence of a specific superovulation protocol or to the response of a particular patient to a standard drug regimen [4].

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Fig. 16.2

The advent of ICSI requiring removal of the cumulus cells has changed this assessment and has allowed embryologists to characterize oocyte morphology


Interestingly, even the use of LH-containing drugs has been linked to a high recurrence of a particular oocyte dysmorphism, therefore leading to the debate on the role of urinary gonadotropins, native or purified, versus the recombinant FSH drugs [5, 6]. These oocyte characterizations evidenced an array of defects affecting its ability to undergo fertilization or to support the development of the resulting conceptus, albeit in an inconsistent manner.


Indeed, several investigations that probed the causative effect of oocyte morphology on embryo development and implantation have led to the debate ignited by studies identifying certain ooplasmic features significantly impairing fertilization and embryo quality [7] with other studies finding no correlation between clinical outcome and this particular attribute [810]. Furthermore, specific oocyte defects such as a dark ooplasmic area and a granular cytoplasm were described as being associated with poor embryo developmental quality [11, 12] (Fig. 16.3). A meta-analysis on the effect of oocyte morphological characteristics in relation to clinical outcome concluded that based on the data from eligible studies, metaphase-II oocytes with a large polar body, large perivitelline space, refractile bodies, or vacuoles were associated with an impaired fertilization rate; however, these phenomenon did not, for any of these defects, significantly affect embryo quality [13]. This lack of causation of oocyte dysmorphism on embryo quality was also corroborated by a systematic review published during the same year that in addition failed to evidence a correlation of oocyte features with its ability to undergo fertilization [3].

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Fig. 16.3

Granular cytoplasm


Here we plan to revisit the occurrence and variety of specific ootid anomalies detected at the time of ICSI, in our own setting and population, to evaluate the eventual ability of these eggs to be fertilized, and to measure the competence of the resulting conceptus to implant. To control for a subtle effect inferred by ooplasmic dysmaturity, the data were analyzed in couples where at least 70% of the oocytes retrieved were at metaphase-II. Finally, in order to control for oocyte aneuploidy, the analysis was then carried out on couples with a female partner ≤35 years old.


16.1 Morphological Description


The terminology to describe oocyte morphology has generally found a consensus among the different laboratories with only small differences in nomenclature. For the purpose of analyzing the significance of each feature in relation to the oocyte function, we have categorized them into four groups: nuclear, cytoplasmic, zona pellucida, and shape/size. When assessing metaphase-II oocytes at the time of ICSI (carried out at a magnification of 400×), annotations were typically made for each individual oocyte detailing any dysmorphism observed by the ICSI operator. A normally developed metaphase-II oocyte should have a spherical zona pellucida enclosing a clear ooplasm and a distinct first polar body [14]. In a cohort of 129,412 oocytes assessed at our center over a 10-year period, of all the morphological features, the top three most represented aberrations were a granular cytoplasm (6.07%), dark central granularity (5.76%), and a large perivitelline space (4.72%).


Among the functional categories, the nuclear defects were the least prevalent occurring at 0.3% of all oocytes assessed. Nuclear defects entail any irregularity of the first polar body such as a fragmented polar body, an abnormally large polar body, or an extrusion of more than one polar body (Table 16.1, numbers 1–3).


Table 16.1

Cytoplasmic dysmorphic patterns

























































































Nuclear


1. Fragmented PB


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285 (0.22%)


2. Large polar body


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19 (0.01%)


3. Two polar bodies


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61 (0.04%)


Cytoplasmatic


4. Inclusions


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3602 (2.8%)


5. Refractile bodies


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1545 (1.2%)


6. Smooth endoplasmic reticulum


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1454 (1.1%)


7. Central granulation/dark center


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7452 (5.8%)


8. Vacuoles


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3483 (2.7%)


9. Granular cytoplasm


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7852 (6.1%)


10. Mottled cytoplasm


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56 (0.04%)


Zona Pellucida


11. Expanse of the perivitelline space


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6106 (4.7%)


12. Debris within perivitelline space


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2288 (1.8%)


13. Dark zona pellucida


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1149 (0.9%)


14. Thin zona pellucida


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184 (0.1%)


15. Abnormal zona pellucida


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653 (0.5%)


16. Bi-layered zona


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40 (0.03%)


Shape/Size


17. Oocyte irregular in shape


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783 (0.6%)


18. Oval oocyte


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859 (0.7%)


19. Giant oocyte


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234 (0.2%)


The cytoplasmic dysmorphic patterns (Figs. 16.4, 16.5, 16.6, 16.7, 16.8, 16.9, and 16.10) are instead among the most prevalent, with 19.7% of oocytes presenting with a distinctive ooplasmic characteristic. The cytoplasm can present inclusions, refractile bodies, smooth endoplasmic reticulum, a central granulation referred to as dark center, vacuoles, granular cytoplasm, and mottled cytoplasm, i.e., a heterogenous, marked patterns of granularity that are not uniform (Table 16.1, numbers 4–10).

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Fig. 16.4

Granular cytoplasm and vacuoles


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Fig. 16.5

Large polar body


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Fig. 16.6

Cytoplasmatic vacuoles


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Fig. 16.7

Large perivitelline space with oocyte dysmorphism


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Fig. 16.8

Large perivitelline space


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Fig. 16.9

Refractile bodies


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Fig. 16.10

Smooth endoplasmatic reticulum


The next most recurrent category at 8.1% concerns irregularities related to the zona pellucida such as a large perivitelline space, perivitelline debris, a dark zona pellucida, a thin zona pellucida, an abnormally shaped zona pellucida, and a bi-layered zona pellucida (Table 16.1, numbers 11–16).


The last category, shape/size at the frequency of 1.4%, entails irregularities of contour of the oocyte defined as irregular, oval, or in size, characterized by a large cytoplasmic volume. Although the shape of the oocyte has not been found to be linked to fertilization or day 3 embryo quality [3, 15], giant oocytes (Fig. 16.11), verisimilarly generated by the fusion of two prophase-I oocytes and often characterized by the presence of two polar bodies, have been found to have a higher incidence of aneuploidy and/or multiple-ploidy [16, 17].

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Fig. 16.11

Giant oocyte


16.2 Clinical Outcome


From October 2008 to May 2018, a total of 10,329 patients were treated in 12,580 ICSI cycles with at least five oocytes injected were included in the analysis with an average male partner age of 39.7 ± 7 years and a female partner 37.3 ± 5 years. Of these cycles, 58.6% had at least one oocyte with a morphological defect. Cycles that had inadequate ejaculated sperm parameters for ICSI (<1 million/mL) or that used surgically retrieved spermatozoa were excluded.


Superovulation was carried out by considering multiple factors such as patient weight, age, serum anti-mullerian hormone (AMH) level, antral follicular count, and any history of previous response to stimulation protocols. Patients were super-ovulated with gonadotropins daily (Gonal F, EMD Serono, Geneva, Switzerland; Menopur, Ferring Pharmaceuticals Inc., Parsippany, NJ, USA; and/or Follistim, Merck, Kenilworth, NJ, USA). Suppression of pituitary gland function was achieved by administering either a GnRH-antagonist (Ganirelix acetate, Merck, Kenilworth, NJ, USA; or Cetrotide, EMD-Serono Inc., Rockland, MA, USA) or GnRH-agonists (leuprolide acetate, Abbott Laboratories, Chicago, IL, USA). Ovulation was triggered with human chorionic gonadotropin (hCG, Ovidrel, EMD Serono) once the two lead follicles were at least 17 mm in diameter. Oocyte retrieval was performed 35–37 h post-trigger under conscious sedation [18].


We stratified these cases according to the percentage of oocytes displaying morphological anomalies in quartiles ranging from 0–24%, 25–49%, 50–74%, and 75–100% of oocytes having an annotation regarding a particular morphological feature. Clinical outcome including fertilization, clinical pregnancy, implantation, deliveries, and pregnancy loss were recorded and compared.


We found that the fertilization, clinical pregnancy, and implantation rates progressively decreased as the cycles increased in the percentage of oocytes with a dysmorphism (P < 0.00001), particularly in the groups of 75–100% (Table 16.2). The delivery and ongoing rates progressively decreased with the increasing proportion of dysmorphic oocytes (P < 0.00001). The inverse occurred with the pregnancy loss (P < 0.05) when the oocyte defects appeared at a rate over 25% (Table 16.2).
Mar 28, 2021 | Posted by in OBSTETRICS | Comments Off on of Oocyte Morphology on ICSI Outcomes
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