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Year : 2020  |  Volume : 4  |  Issue : 1  |  Page : 60-62

Successful pregnancy following transfer of embryo with dissolved zona pellucida

Reproductive Medicine Centre, The First Hospital of Lanzhou University; Key Laboratory for Reproductive Medicine and Embryo of Gansu, Lanzhou 730000, China

Date of Submission27-Sep-2019
Date of Decision28-Oct-2019
Date of Acceptance04-Dec-2019
Date of Web Publication2-Apr-2020

Correspondence Address:
Hong-Xing Li
Reproductive Medicine Hospital of The First Hospital of Lanzhou University, No. 1 Donggang West Road, Lanzhou, Gansu 730000
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2096-2924.281856

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This study aimed to describe a case of a patient with the spontaneous dissolution of zona pellucida (ZP) during cleavage embryo development after intracytoplasmic sperm injection (ICSI). This patient experienced early abortion due to fetal chromosome 8 abnormality and received ICSI at 31 years of age. Time-lapse monitoring of embryo cleavage and blastocyst culture was performed, and we found that the ZP of embryos 1, 2, 4, and 5 dissolved gradually during the cleavage stage of embryo development. Five blastocysts that developed from 2 pronuclear zygotes were analyzed using next-generation sequencing, and one frozen-thawed blastocyst was transferred, resulting in intrauterine pregnancy. The results of amniotic fluid puncture showed normal fetal chromosomes. To our knowledge, this is the first report of ZP dissolution during the cleavage-stage embryo; however, the exact mechanism remains unknown. The morphological changes inferred that the granular matter in the periocular space was related to the dissolution of ZP through time-lapse observation.

Keywords: Blastocyst Transfer; Intracytoplasmic Sperm Injection; Next-Generation Sequencing; Zona Pellucida Dissolution

How to cite this article:
Li HX. Successful pregnancy following transfer of embryo with dissolved zona pellucida. Reprod Dev Med 2020;4:60-2

How to cite this URL:
Li HX. Successful pregnancy following transfer of embryo with dissolved zona pellucida. Reprod Dev Med [serial online] 2020 [cited 2020 May 26];4:60-2. Available from: http://www.repdevmed.org/text.asp?2020/4/1/60/281856

  Introduction Top

The zona pellucida (ZP) is a glycoprotein that coats the surface of the egg. Its role is to protect the egg and prevent the entry of heterologous sperm.[1] There is a layer of secretory vesicles underneath the ZP of eggs called cortical granules. The release of these cortical granules via efflux during fertilization can cause changes in the ZP structure, forming a fertilized membrane, and preventing other sperms from entering.[2],[3],[4] Usually, the ZP ruptures after blastocyst formation and growth, consequently, the blastocyst hatches. Here, we describe a rare case of a patient who successfully became pregnant following embryo transfer with spontaneously dissolved ZP after intracytoplasmic sperm injection (ICSI).

  Case Report Top

A 31-year-old woman with 4 years of secondary infertility related to male-factor infertility underwent ICSI treatment at our reproductive center after early abortion due to fetal chromosome 8 abnormality. A mild stimulation protocol was followed for 9 days using gonal-F (150 units every day, Merck Serono, Switzerland). Thirty-six hours before egg collection, we administered 5,000 IU of human chorionic gonadotropin (hCG, IBSA, Switzerland) to trigger oocyte maturation. Nine mature oocytes were collected, of which, six were fertilized via ICSI and cultured in time-lapse incubators (Embryoscope, Unisense-Fertilitech, Denmark). All the embryos enrolled in this study were individually cultured under oil, in sequential media (Quinn's Advantage Medium; SAGE, USA), at 37°C, 5% O2, 6% CO2. It is noteworthy that after the pronucleus disappeared, the ZP of four zygotes dissolved gradually with granules in the perivitelline space (PVS) [Figure 1] and [Supplementary Video 1, embryos 1, 2, 4, 5] discovered using time-lapse image comparison. A comparison of time-lapse morphokinetic parameters and embryos score is presented in [Table 1]. Blastocyst biopsy was performed on embryos 1–5 on the 5th and 6th day after embryo culture. The biopsy samples were subjected to genome-wide amplification and next-generation sequencing (NGS, Illumina, America) detection. The NGS results were as follows–embryo 1: aneuploidy, trisomy 2 and trisomy 9; embryo 2: euploid; embryo 3: aneuploidy, trisomy 1; embryo 4 and 5: euploid and abnormal chromosome fragments, del(12)(q12-q24.33) and del(mosic)(22)(q11.21-q13.31), respectively.
Figure 1: Spontaneously dissolved zona pellucida present partially during blastulation. (a-d) The morphological characteristics of the embryo at 17, 26, 68, and 118 h successively after intracytoplasmic sperm injection

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Table 1: Comparison of the TLM parameters and blastocysts score of embryos 1–6

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Frozen-thawed embryo transfer was performed after normal size follicle ovulations. The second embryo (embryo 2) was transferred into the uterine cavity. At 6 weeks of gestation, fetal heartbeat was clinically diagnosed. At 18 weeks of gestation, the results of amniocentesis confirmed that the fetal chromosomes were completely normal. A baby girl weighing 3,750 g was normally born at 39 weeks of gestation.

  Discussion Top

The ZP is mainly composed of glycoproteins secreted by the egg and other cells. Few ZP presents translucent and dense and has irregular protrusions. Zhao et al. found that ICSI could improve the likelihood of fertilization of oocytes in the presence of abnormal ZP.[1] Till date, several ZP gene variants have been identified in patients with oocyte anomalies.[2] Margalit et al. reported that abnormal oocyte ZP may not have been due to the genetic changes in the ZP genes.[3] It has been indicated that extra cytoplasmic dysmorphisms should be considered only as phenotypic deviations.[4] However, two retrospective studies found that an oocyte cohort affected by both large PVS and PVS granularity showed compromised implantation and pregnancy rates.[5],[6] Setti et al. demonstrated that the presence of large first polar body, large PVS, refractile bodies, or vacuoles was associated with decreased oocyte fertilization.[7] Under the ZP, there is a layer of secretory vesicles called cortical granules. The release of these granules via efflux during fertilization causes changes in the ZP structure and prevents other sperms from entering. The first step in hatching of the blastocyst is the formation of a gap in the ZP. The expanding blastocyst will exert mechanical, hydrostatic pressure on the ZP.[8] The trypsin-like protease synthesized by the trophoblast cells exerts a certain digestive effect on ZP.[9] However, to our knowledge, the dissolution of ZP in the cleavage-stage embryos has not been reported.

In this case, there were many granular substances in the PVS of embryos 1–5. It is noteworthy that as compared to embryos 1, 2, 4, and 5, embryo 3 had less particulate matter, and its ZP disappeared later. There was no particulate matter in the periovum space of embryo 6, and the ZP remained unchanged during the whole culture process. These morphological changes inferred that there might be some correlation between the granular matter in the periocular space and the dissolution of ZP. In conclusion, to our knowledge, this is the first report of ZP dissolution during the cleavage-stage embryo, and the exact mechanism remains unknown. Normal embryos can be selected using NGS technology.

Consent for publication

Written informed consent was obtained from the patient for publication of their case and any accompanying images.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.


The author would like to thank Caixia Ma and Lei Xiao for English language editing.

Financial support and sponsorship

The Scientific Research Fund of theFirst Hospital of Lanzhou University, No. ldyyyn2018-11.

Conflicts of interest

There are no conflicts of interest.

  References Top

Zhao J, Zhang NY, Xu ZP, Chen LJ, Zhao X, Zeng HM, et al. Effects of abnormal zona pellucida on fertilization and pregnancy in IVF/ICSI-ET. J Reprod Contracept 2015;26:73-80. doi: 10.7669/j.issn. 1001-7844.2015.02.0073.  Back to cited text no. 1
Yang P, Luan X, Peng Y, Chen T, Su S, Zhang C, et al. Novel zona pellucida gene variants identified in patients with oocyte anomalies. Fertil Steril 2017;107:1364-9. doi: 10.1016/j.fertnstert.2017.03.029c.  Back to cited text no. 2
Margalit M, Paz G, Yavetz H, Yogev L, Amit A, Hevlin-Schwartz T, et al. Genetic and physiological study of morphologically abnormal human zona pellucida. Eur J Obstet Gynecol Reprod Biol 2012;165:70-6. doi: 10.1016/j.ejogrb.2012.07.022.  Back to cited text no. 3
Balaban B, Urman B. Effect of oocyte morphology on embryo development and implantation. Reprod Biomed Online 2006;12:608-15. doi: 10.1016/S1472-6483(10)61187-X.  Back to cited text no. 4
Farhi J, Nahum H, Weissman A, Zahalka N, Glezerman M, Levran D. Coarse granulation in the perivitelline space and IVF-ICSI outcome. J Assist Reprod Genet 2002;19:545-9. doi: 19:545-9.10.1023/a: 1021243530358.  Back to cited text no. 5
Ferrarini Zanetti B, Paes de Almeida Ferreira Braga D, Souza Setti A, de Cássia Sávio Figueira R, Iaconelli A Jr., Borges E Jr. Is perivitelline space morphology of the oocyte associated with pregnancy outcome in intracytoplasmic sperm injection cycles? Eur J Obstet Gynecol Reprod Biol 2018;231:225-9. doi: 10.1016/j.ejogrb.2018.10.053.  Back to cited text no. 6
Setti AS, Figueira RC, Braga DP, Colturato SS, Iaconelli A Jr., Borges E Jr. Relationship between oocyte abnormal morphology and intracytoplasmic sperm injection outcomes: A meta-analysis. Eur J Obstet Gynecol Reprod Biol 2011;159:364-70. doi: 10.1016/j.ejogrb. 2011.07.031.  Back to cited text no. 7
Montag M, Koll B, Holmes P, van der Ven H. Significance of the number of embryonic cells and the state of the zona pellucida for hatching of mouse blastocysts in vitro versus in vivo. Biol Reprod 2000;62:1738-44. doi: 10.1095/biolreprod62.6.1738.  Back to cited text no. 8
Ny T, Wahlberg P, Brändström IJ. Matrix remodeling in the ovary: Regulation and functional role of the plasminogen activator and matrix metalloproteinase systems. Mol Cell Endocrinol 2002;187:29-38. doi: 10.1016/S0303-7207(01)00711-0.  Back to cited text no. 9


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