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 Table of Contents  
Year : 2019  |  Volume : 3  |  Issue : 4  |  Page : 252-255

The cumulus cells and oocytes: A systematic review of extended culture for intracytoplasmic sperm injection

1 Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
2 Department of Gynecology and Obstetrics, Johns Hopkins Medicine, Baltimore, Maryland 21093, USA

Date of Submission15-Sep-2019
Date of Web Publication2-Jan-2020

Correspondence Address:
Ping Xia
Department of Gynecology and Obstetrics, Johns Hopkins Medicine, 10751 Falls Road, Suite 280, Lutherville, Maryland 21093
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2096-2924.274550

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Currently-placed protocols for extended culture for in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are not uniformly standardized in determining the optimal stage of oocyte maturation for maximizing clinical outcomes. The objective of this systematic review is to elucidate the relationship between extended cumulus-oocyte culture and its effect on the clinical outcomes of IVF/ICSI. We included an electronic search on PubMed Central as well as the Journal of Fertility and Sterility to yield seven studies on extended oocyte culture for IVF/ICSI. Four of the seven investigations illustrate the promising beneficial relationship of extended culture with conditioned or supplemented media to mimic physiological uterine conditions. Three studies did not capture beneficial relationships between extended oocyte culture and clinical outcomes with unconditioned, unsupplemented maturation medium. Improvement in fertilization rates, oocyte development, and live birth rates may be achieved by extended culture with the addition of supplemental biochemicals. The usage of follicular fluid, cumulus cells, and meiotic inhibitors imitates the physiological in vivo conditions, whereas extended oocyte culture imitates in vivo temporal conditions. The conjunction of extended oocyte culture with supplemented metabolites, either added in maturation media manually or secreted by cumulus-oocyte complexes, mimics natural uterine physiological conditions to improve clinical outcomes for patients seeking IVF/ICSI.

Keywords: Cumulus Cells; Extended Culture; In vitro Fertilization; Intracytoplasmic Sperm Injection; Oocyte

How to cite this article:
Truong SK, Singh B, Xia P. The cumulus cells and oocytes: A systematic review of extended culture for intracytoplasmic sperm injection. Reprod Dev Med 2019;3:252-5

How to cite this URL:
Truong SK, Singh B, Xia P. The cumulus cells and oocytes: A systematic review of extended culture for intracytoplasmic sperm injection. Reprod Dev Med [serial online] 2019 [cited 2020 Jul 7];3:252-5. Available from: http://www.repdevmed.org/text.asp?2019/3/4/252/274550

  Introduction Top

In assisted reproductive technology (ART), extended culture refers to the temporal extension between egg collection and insemination by in vitro fertilization and intracytoplasmic sperm injection (IVF/ICSI). The potentiality of extended culture to improve clinical outcomes such as oocyte quality, fertilization rate, embryonic quality, pregnancy, and live birth rates serves promising for addressing infertility that affects over 15% of women aged 15–44 years.[1]

In particular, the extracellular environment of the oocyte has been subjected to much research on the nourishing relationship between cumulus cells on oocytes. Cumulus cells portray a vital role in signaling proper maturation of oocytes by the release of various biochemical compounds and metabolites, correlating significantly improved implantation and pregnancy rates of oocytes incubated with cumulus cells.[1] Cumulus cells hold a potential role in proper oocyte genetic transcription and in selecting quality sperm [2],[3] by its secretory products, such as progesterone, lysophosphatidylcholine, and phytosphingosine – all potential factors in inducing the acrosome reaction.[4] In addition, oocyte-dependent activation of MTOR in cumulus cells has been shown to improve cumulus–oocyte complex (COC) survival and development by suppression of Dditl4, an inhibitor of MTOR.[5] Oocyte aging involves the signaling of soluble Fas ligand (sFasL) expressed by cumulus cells to bind to steady levels of Fas receptor for up to 24 h. It has been shown that COCs have exhibited a greater number of released metabolites (369) in maturation media compared to 173 biochemical components found in the media of denuded oocytes.[6] Thus, the presence of cumulus cells directly correlates to a greater number of biochemical signals released into the surrounding maturation media, yielding improved blastocyst development following insemination.[6] As a result, cumulus cells adopt a physiological role in COC survival and selection of functionally competent sperm. These results implicate that allowing enough time for cumulus cells to provide essential signaling biomolecules may improve oocyte development and insemination rates, affecting clinical IVF/ICSI outcomes. Extended culture of oocytes with cumulus cells and/or various biochemical supplements may prove fruitful in improving clinical outcomes.

  Methods Top

To find eligible studies on the effects of extended culture on clinical outcomes in ART, an electronic search was made on two databases, namely PubMed Central and the Journal of Fertility and Sterility. This search yielded 10,822 related publications to the terms “extended culture”, and was further filtered down to 271 titles containing “oocyte” and related concepts [Figure 1]. One reviewer (SKT) categorized the papers into topics based on their titles and abstracts. All papers categorized as “Oocyte Maturation” were thoroughly read and seven studies were selected, garnering research on extended culture of over 5,865 of human oocytes,[7],[8],[9],[10],[11] as well as bovine and mouse oocytes.[12],[13]
Figure 1: PRISMA diagram of study selection

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  Results Top

Included studies of extended culture

Five of the seven studies revealed improved clinical outcomes of fertilization, oocyte development, pregnancy, and live birth rates.[8],[10],[11],[12],[13] They included additional supplements such as COCs, follicular fluid, and/or various meiotic inhibitors to the extended culture. Two studies by Reichman et al.[7] and Bárcena et al.[9] showed no difference or decreased rates in at least one clinical outcome investigated on denuded human oocytes without any conditioned maturation media.[7],[9] One study conducted by Yoon et al.[13] recorded recovered blastocyst developmental rates following cryopreservation by extended culture of the oocyte prior to insemination. [Table 1] summarizes the data of the main studies.
Table 1: Data summary of main studies on extended oocyte culture on the clinical outcomes of IVF/ICSI

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Extended oocyte culture effects on fertilization

Of the six studies that investigated the effect of extended oocyte culture on fertilization rates, four witnessed improved fertilization rates. The two outlier studies [7],[9] did not note any significant discordance of fertilization rates from extended, denuded oocyte culture.

Studies by Pujol et al.[8] and Papaioannidou et al.[10] documented improved fertilization rates in ICSI of extended culture of human oocytes, with the latter incubating oocytes in follicular fluid; both inseminations were by ICSI protocols.[14] In addition, two more studies by Wilding et al.[11] and Farghaly et al.[12] captured improved fertilization rates by ICSI (56% vs. 42% and 46% vs. 40%, respectively) with extended incubation in either follicular fluid or meiotic inhibitors.

Extended oocyte culture effects on oocyte development

Six studies reported results on the influence of extended culture on oocyte development. Four studies [10],[11],[12],[13] found improvements on oocyte maturation and quality by including COCs, follicular fluid, and/or meiotic inhibitors in extended incubation.

Extended oocyte culture effects on pregnancy

Five of the seven studies [7],[8],[9],[10],[11] recorded clinical pregnancy outcomes in extended human oocyte culture. Two of the five studies [7],[9] failed to observe statistically significant relationships between extended culture and pregnancy rates. One study [8] noted decreased clinical pregnancy rates (−7.7%/h). However, another study [11] recorded improved pregnancy rates by extended culture of COCs in follicular fluid for IVF (56% vs. 38%) and ICSI (56% vs. 42%). One study [10] achieved a successful twin pregnancy by extended culture of immature oocytes with follicular fluid.

Extended oocyte culture effects on live birth

Three studies [7],[8],[9] did not record statistical differences on live birth rates between standard and extended oocyte culture.[15] However, the experiment by Wilding et al.[11] relayed improved live birth rates from extended culture for IVF (27% vs. 19%) and ICSI (25% vs. 18%). It is the only study out of the four [10],[11],[12],[13] reporting live birth rates that supplemented the extended culture media of COCs with follicular fluid or meiotic inhibitors.

  Discussion Top

Oocyte maturation in extended culture

The four studies [10],[11],[12],[13] that reveal general improvements in fertilization rates, proper oocyte and embryonic development, and/or live birth rates from extended oocyte culture all included the addition of cumulus cells, supplemental fluids, or meiotic inhibitors. Extended culture and important biochemicals and metabolites, provided in vitro or secreted by cumulus cells, better mimic in vivo physiological and temporal conditions to improve clinical outcomes for patients seeking IVF/ICSI. COCs and follicular fluid may be key in fostering a buffered environment as an important cell communication medium for oocyte maturation.[13]

With these supplements serving to mimic the biochemicals signaled in vivo, perhaps, the extended culture of COCs will provide ample time for the cumulus cell signaling to properly mature oocytes at an appropriate pace in vitro, especially with the current knowledge of speed imbalances between the nuclear and cytoplasmic maturation of oocytes in ART.[16] The use of cumulus cells in extended culture may prove necessary for proper oocyte maturation.

Future directions

Striving for in vivo conditions, in vitro

In review of the seven core studies, what proves key to improving the clinical outcomes of IVF/ICSI is how closely in vitro conditions mimic the conditions in vivo for the developing oocyte. While extended culture alone may better mimic the temporal timeline of oocyte development, many currently-placed protocols for IVF/ICSI at assisted reproduction centers worldwide call for denudation of the oocyte, removing cumulus cells essential for biochemical signaling. In fact, this procedure frequently results in compromised oocyte development for ART procedures.[6] By the addition of follicular fluid and meiotic inhibitors, increased clinical outcomes are witnessed in the studies.[10],[11],[12],[13] However, not enough research has been explored in the realm of extended culture with respect to COCs. Cumulus cells hold promising capabilities to influence oocyte development by releasing secretory factors with chemotaxis attraction properties,[3] prolonging oocyte survival by MTOR activation,[5] accelerating oocyte maturation by sFasL production,[17] and improving implantation and pregnancy rates in ICSI.[1] Novel studies have explored revolutionary cumulus cell biomarkers to predict proper blastocyst formation and pregnancy,[18] propelling the field of ART toward the vital role cumulus cells play in the various molecular signaling pathways of the developing oocyte.[19] Further research on extended culture with the presence of cumulus cells must be explored to achieve not only better physiological conditions in vitro, but also to refine our current IVF/ICSI protocols to maximize clinical outcomes.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Bhadarka HK, Patel NH, Patel NH, Patel M, Patel KB, Sodagar NR, et al. Impact of embryo co-culture with cumulus cells on pregnancy and implantation rate in patients undergoing in vitro fertilization using donor oocyte. Indian J Med Res 2017;146:341-5. doi: 10.4103/ijmr.IJMR_1702_15.  Back to cited text no. 1
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Bárcena P, Rodríguez M, Obradors A, Vernaeve V, Vassena R. Should we worry about the clock? Relationship between time to ICSI and reproductive outcomes in cycles with fresh and vitrified oocytes. Hum Reprod 2016;31:1182-91. doi: 10.1093/humrep/dew070.  Back to cited text no. 9
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Wilding M, Singer M, Fehr P, Haeberlin F, Roth F, Lachat R, et al. The effect of extended culture of cumulus-oocyte complexes in follicular fluid during in vitro fertilisation cycles. J Assist Reprod Genet 2006;23:129-36. doi: 10.1007/s10815-005-9016-y.  Back to cited text no. 11
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Zhu J, Zhang J, Li H, Wang TY, Zhang CX, Luo MJ, et al. Cumulus cells accelerate oocyte aging by releasing soluble Fas Ligand in mice. Sci Rep 2015;5:8683. doi: 10.1038/srep08683.  Back to cited text no. 17
Braga DP, Setti AS, Lo Turco EG, Cordeiro FB, Cabral EC, Cortezzi SS, et al. Protein expression in human cumulus cells as an indicator of blastocyst formation and pregnancy success. J Assist Reprod Genet 2016;33:1571-83. doi: 10.1007/s10815-016-0800-7.  Back to cited text no. 18
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  [Table 1]


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