Human Egg Maturity Assessment and Its Clinical Application

Abstract

The optimal timing of intracytoplasmic sperm injection (ICSI) is of a serious concern for fertility programs because untimely sperm entry diminishes the egg's developmental competence. Presence of the first polar body (PB) together with the meiotic spindle indicates completion of the oocyte maturation and the egg's readiness for fertilization. In clinical practice, it is customary to assume that all oocytes displaying a PB are mature metaphase (MII) oocytes. However, PB extrusion precedes the formation of the bipolar MII spindle. This asynchrony makes the mere presence of PB an unreliable marker of oocyte maturity. Noninvasive spindle imaging using polarized light microscopy (PLM) allows quick and easy inspection of whether the PB-displaying oocyte actually reassembled a meiotic spindle prior to ICSI. Here, we present a standard protocol to perform human egg maturity assessment in the clinical laboratory. We also show how to optimize the time of ICSI with respect to the oocyte's developmental stage in order to prevent premature sperm injection of late-maturing oocytes. Using this approach, even immature oocytes extruding PB in vitro can be clinically utilized. Affirmation that MII spindle is present prior to sperm injection and individual adjustment of the time of ICSI is particularly important in poor prognosis in-vitro fertilization (IVF) cycles with a low number of oocytes available for fertilization.

Live birth achieved despite the absence of ejaculated spermatozoa and mature oocytes retrieved: a case report

“…The principle and methodology of PLM examination, as well as the optimization of the ICSI timing, have been thoroughly described previously [14,15,28,36]. However, it is important to emphasize here that spindle imaging provides no information about chromatin configuration at the metaphase plate.…”

“…However, it is important to emphasize here that spindle imaging provides no information about chromatin configuration at the metaphase plate. Chromosome misalignment and precocious chromatid splitting could occur in oocytes featuring the MII spindle [28,37]. Therefore, younger patients with an unexpectedly inadequate response to ovarian stimulation due to specific genetic background and/or endocrine derangements [38][39][40] are more likely to benefit from PLM-navigated ICSI timing than women of advanced age.…”

“…The cumulus-oocyte complexes were retrieved using ultrasound-guided transvaginal aspiration and collected in dual buffered MHM medium (#90166, Irvine Scientific, USA). The oocyte denudation was carried out 10 min after retrieval to distinguish the in vivo matured eggs from oocytes that complete maturation in vitro and benefit from prolonged incubation before ICSI [14,28]. Despite a good follicular count, no PB-displaying oocytes were obtained.…”

“…However, this oocyte did not show an MII spindle signal during the PLM examination, indicating that the maturation process was not yet completed. Therefore, ICSI was postponed, and the maturation stage of each oocyte was closely monitored, as previously described [28]. During the next 2 h, another 4 oocytes extruded PBs.…”

Cytoplasmic maturation in human oocytes: an ultrastructural study †

“…Prior to fixation, the late-maturing oocytes were incubated in a Continuous Single Culture medium (#90165, CSCM, Irvine Scientific, USA) covered with mineral oil and a humidified atmosphere of 5% O 2 and 6% CO 2 until they reached a distinctive developmental stage of oocyte maturation (GV oocytes 1–3 h; close-to-anaphase MI oocytes 4–6 h, MII-arrested oocytes 6–24 h). The presence of MI/MII spindle was confirmed by polarized light microscopy (OCTAX polarAIDE™, MTG, Germany), as described previously [ 27 ]. The morphology of each oocyte was evaluated by an experienced clinical embryologist, and overall appearance was photographed for documentation purposes.…”