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Year : 2015  |  Volume : 2  |  Issue : 2  |  Page : 67-69

Successful pregnancy after transfer of human blastocysts that had naturally escaped completely from the zona on day 5

1 Assisted Conception Unit, Lister Hospital and Fertility Centre, Airport Hills, Accra, Ghana
2 IVF Consultancy Services, 144a New Walk, Leicester, LE1 7JA, United Kingdom

Date of Web Publication9-Sep-2015

Correspondence Address:
M B Yakass
Assisted Conception Unit, Lister Hospital and Fertility Centre, Accra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2348-2907.164864

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A viable human blastocyst must demonstrate the capacity to expand in vitro and hatch out from its protective zona pellucida after transfer, in order to implant into the endometrial lining. Some blastocysts, however, experience hatching difficulties and remain enclosed within their zonae, preventing implantation after transfer to the uterus. Successful pregnancies have been reported by transferring embryos that have been treated to partially remove the zonae by chemical intervention (e.g. pronase or acid Tyrode's) or mechanical intervention (e.g. by laser or use of assisted hatching pipettes). Complete zonae removal has also been reported prior to embryo transfer. This is a report of a case where expanded blastocysts naturally hatched in vitro and completely escaped from their zonae on day 5 of preimplantation development. The careful transfer of these fully expanded hatched blastocysts on the same day resulted in a successful clinical pregnancy.

Keywords: Blastocyst, epigenetic, imprinting, zona-free, zona pellucida

How to cite this article:
Yakass M B, Woodward B J, Otoo M A, Hiadzi E K. Successful pregnancy after transfer of human blastocysts that had naturally escaped completely from the zona on day 5. IVF Lite 2015;2:67-9

How to cite this URL:
Yakass M B, Woodward B J, Otoo M A, Hiadzi E K. Successful pregnancy after transfer of human blastocysts that had naturally escaped completely from the zona on day 5. IVF Lite [serial online] 2015 [cited 2023 Jan 30];2:67-9. Available from: http://www.ivflite.org/text.asp?2015/2/2/67/164864

  Introduction Top

The relatively low implantation rate of embryos produced from in vitro fertilization – embryo transfer (IVF-ET) has been partly blamed on impaired hatching of the embryos.[1] Although human blastocysts can expand readily in vitro, the majority are unable to completely hatch out of their zonae when transferred into the uterus and subsequently degenerate by day 6 or 7.[2] The role of the zona includes initial binding of the sperm, induction of the acrosome reaction in bound sperm, prevention of multiple sperm penetration in conjunction with the oolemma via the cortical reaction, prevention of blastomere dispersal in the developing embryo and avoidance of direct contact between embryo and foreign cells whilst facilitating passage of the embryo through the  Fallopian tube More Details. It has also been demonstrated that the zona is no longer essential for the continual normal development in vitro once compaction has occurred.[2] It has been theorized that a protease-like enzyme is released in vivo either by the blastocyst itself or by the endometrium which aids with the hatching and subsequent implantation.[3],[4] Successful pregnancies have been reported by transferring embryos that have been treated to remove the zona using pronase [5] or acid Tyrode's.[3],[6] Here, we report a case of thirteen human blastocysts that had all naturally hatched out completely from their zonae on day 5 in vitro without any assisted hatching treatment, and a clinical pregnancy following transfer of three of these fully hatched blastocysts.

  Case Presentation and Outcome Top

This case involved a donor-recipient cycle: The donor was 28-year-old, whilst the recipient was 44-year-old with primary infertility. Culture was performed in Global Total Media (LifeGlobal, Brussels, Belgium) using a Cook Mini-incubator (MINC, Cook, Australia) supplied with a trigas mixture of 6% carbon dioxide, 5% oxygen and 89% nitrogen (BOC, UK). Thirty-three normally fertilized embryos resulted following conventional IVF and were cultured to day 5. On the morning of day 5, three embryos had achieved the expanded blastocyst stage whilst the remaining embryos were either at the early blastocyst or compacting morula stage. On the evening of day 5, at 123 h post insemination, thirteen fully expanded blastocysts had naturally hatched and completely escaped from their zona pellucidae without any assisted hatching intervention [Figure 1]. Three zona-free blastocysts with the best grades (most expanded with clearly defined good quality inner cell masses and trophectoderms) were carefully loaded into a KJETS 7019 SIVF (Cook, Australia) catheter and transferred to the uterus under ultrasound guidance. Ten zona-free blastocysts were vitrified. A blood test performed 14 days after transfer confirmed a positive pregnancy and ultrasound scan at 6 weeks showed development of a single in-utero gestational sac.
Figure 1: Two of the several completely hatched blastocysts (one slightly collapsed)

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  Discussion Top

There have been several reports of successful pregnancies by transferring embryos that have been treated to remove the zona by pronase [5] or acid Tyrode's.[3],[6] From this case report, we support and agree with the view that the blastocysts secrete an enzyme on their own which aids complete hatching from the zona for subsequent implantation in the endometrium. The excellent development of these embryos to hatch on their own on day 5 reflects optimal culture conditions, as culturing under suboptimal conditions can deleteriously impact on embryo quality and progression through subsequent stages of pre-implantation development in vitro.[7]

It is of interest that the same culture conditions were used for all patients treated at our institution, yet this natural phenomenon of complete zona hatching by so many embryos on day 5 has never been witnessed to date, or since. One might speculate that there could possibly be an intrinsic/epigenetic factor that engendered these particular embryos to grow so well and therefore be able to hatch out completely by day 5. Since in vitro embryo development may be delayed in culture compared to in vivo development, embryos that develop more quickly have historically been considered to be more viable because they are thought to more closely follow the typical in vivo timeline.[7] However, in contrast another study found that faster-growing embryos exhibited more perturbation in genomic imprinting, suggesting an inability to faithfully maintain epigenetic information when embryos transition too rapidly through the first few embryonic divisions.[8] Whilst the complete unaided hatching of thirteen embryos on day 5 was considered a positive indication of embryo quality, the successful implantation and development of only one embryo after transfer may indicate that viability may have been compromised in the other two transferred embryos. Further research is needed to appreciate the epigenetics and genomic imprinting of pre-implantation embryos that can fully hatch in vitro on day 5 without intervention.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Cohen J. Assisted hatching of human embryos. J in vitro Fert Embryo Transf: IVF 1991;8:179-90.  Back to cited text no. 1
Fong CY, Bongso A, Ng SC, Anandakumar C, Trounson A, Ratnam S. Ongoing normal pregnancy after transfer of zona-free blastocysts: Implications for embryo transfer in the human. Hum Reprod 1997;12:557-60.  Back to cited text no. 2
Cohen J, Alikani M, Reing AM, Ferrara TA, Trowbridge J, Tucker M. Selective assisted hatching of human embryos. Ann Acad Med Singapore 1992;21:565-70.  Back to cited text no. 3
Fong CY, Bongso A, Sathananthan H, Ho J, Ng SC. Ultrastructural observations of enzymatically treated human blastocysts: Zona-free blastocyst transfer and rescue of blastocysts with hatching difficulties. Hum Reprod 2001;16:540-6.  Back to cited text no. 4
Fong CY, Bongso A, Ng SC, Kumar J, Trounson A, Ratnam S. Blastocyst transfer after enzymatic treatment of the zona pellucida: Improving in vitro fertilization and understanding implantation. Hum Reprod 1998;13:2926-32.  Back to cited text no. 5
Mansour RT, Rhodes CA, Aboulghar MA, Serour GI, Kamal A. Transfer of zona-free embryos improves outcome in poor prognosis patients: A prospective randomized controlled study. Hum Reprod 2000;15:1061-4.  Back to cited text no. 6
La Salle S. Growing fast or slow: What makes the best embryo? Biol Reprod 2012;86:142, 1-2.  Back to cited text no. 7
Market Velker BA, Denomme MM, Mann MR. Loss of genomic imprinting in mouse embryos with fast rates of preimplantation development in culture. Biol Reprod 2012;86:143, 141-116.  Back to cited text no. 8


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