An observational study in Infertility and Donor Oocyte Assisted Reproduction, sponsored by Center for Reproductive Medicine Bocian. Active, not recruiting at 1 site in Poland. Open to female participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-29.
Sponsored by Center for Reproductive Medicine Bocian · Observational
This multicenter retrospective observational study compares embryological and clinical outcomes following treatment with fresh versus vitrified-warmed donor oocytes at Bocian Fertility Clinic centers in Poland. The study focuses on a standardized allocation strategy in which recipients are intended to receive six mature (metaphase II, MII) donor oocytes. In the vitrified-warmed group, oocytes are cryopreserved at the MII stage and subsequently warmed for use. Oocytes lost during warming are not routinely replaced, allowing the study to evaluate the consequences of warming-related losses within the initial allocation. The study will assess fertilization, embryo development, usable blastocyst yield, the probability of obtaining an embryo for transfer, and live birth following the first embryo transfer originating from the allocated oocytes. Clinical effectiveness will be evaluated from the initial oocyte allocation, including cycles in which no embryo transfer occurs. The objective is to determine whether fresh and vitrified-warmed donor-oocyte strategies are associated with differences in embryological efficiency and the likelihood of live birth when the initial number of mature allocated oocytes is standardized.
Background and rationale Fresh and vitrified-warmed donor oocytes are widely used in assisted reproductive technology. Although modern vitrification has substantially improved oocyte survival, comparisons between fresh and warmed oocytes may be complicated by differences in the number of oocytes allocated to recipients and by the use of outcome measures restricted to cycles reaching embryo transfer. This study examines the entire reproductive pathway beginning with a standardized initial allocation of six mature donor oocytes. The approach allows the assessment of both quantitative losses associated with warming and subsequent embryological and clinical outcomes.
Study design and population This is a multicenter, retrospective, observational cohort study using routinely collected clinical and laboratory data from Bocian Fertility Clinic centers in Poland. Eligible donor-oocyte treatment cycles occurring up to September 30, 2026, will be evaluated. Two groups will be compared: recipients treated with fresh donor oocytes and recipients treated with vitrified-warmed donor oocytes.
Oocyte allocation and laboratory assessment Under the standard program, six mature donor oocytes are allocated to a recipient. In the fresh strategy, six mature oocytes are made available for intracytoplasmic sperm injection (ICSI). In the vitrified-warmed strategy, donor oocytes are vitrified at the MII stage, generally stored in groups of three per carrier, and warmed for treatment. Losses during warming are not routinely compensated for by warming additional oocytes. The study will examine the number of oocytes available for ICSI, normally fertilized oocytes (2PN), embryo development, blastocyst formation, and the number of usable blastocysts. Outcomes will be expressed using both the initial allocation and relevant stage-specific denominators.
Clinical outcomes The primary clinical outcome will be live birth following the first embryo transfer derived from the initial oocyte allocation, expressed per recipient allocation. Cycles without embryo transfer will remain in the initial cohort denominator. Live birth per performed first embryo transfer will be evaluated separately.
Where sufficiently complete follow-up is available, cumulative live birth outcomes arising from embryos obtained from the same initial allocation may also be examined.
Analysis Associations between oocyte strategy and reproductive outcomes will be assessed while considering relevant donor, recipient, paternal, calendar-period, and center characteristics. Repeated contributions from the same oocyte donor will be accounted for where linkage data permit.
The study is observational and does not alter routine treatment, oocyte allocation, vitrification, warming, fertilization, embryo culture, or embryo transfer procedures.
2,085 studies on the registry are indexed under Infertility; 357 are open to participants now.
This study's planned enrollment of 3,000 is above the median of 200 across 592 observational studies indexed under Infertility.
Browse Infertility studies →Center for Reproductive Medicine Bocian is the lead sponsor of 2 studies on the registry; none are open to participants now.
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The study population comprises adult female recipients undergoing assisted reproductive treatment with fresh or vitrified-warmed donor oocytes at Bocian Fertility Clinic centers in Poland. Participants will be identified retrospectively from routinely collected clinical and embryology databases. The principal analytical cohort includes recipient treatment cycles with an identifiable initial allocation of six mature donor oocytes. Outcomes will be evaluated from the initial allocation, irrespective of subsequent fertilization, embryo development, or embryo transfer.
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Exclusion Criteria:
Recipients undergoing assisted reproduction using fresh mature (metaphase II, MII) donor oocytes. Under the standard allocation strategy, six fresh MII oocytes are allocated to each recipient and made available for intracytoplasmic sperm injection (ICSI). Embryological and clinical outcomes are evaluated from the initial oocyte allocation, including cycles without embryo transfer.
Procedure: Fresh Donor Oocyte ICSI
Recipients undergoing assisted reproduction using donor oocytes vitrified at the mature (metaphase II, MII) stage. Under the standard allocation strategy, six vitrified MII oocytes, typically stored on two carriers containing three oocytes each, are allocated and warmed for treatment. Oocytes that do not survive warming are not routinely replaced with additional oocytes. Embryological and clinical outcomes are evaluated from the initial allocation of six MII oocytes, including warming-related losses and cycles without embryo transfer.
Procedure: Vitrified-Warmed Donor Oocyte ICSI
Recipients underwent routine ICSI using fresh mature donor oocytes. Under the standard allocation strategy, six MII oocytes were allocated to each recipient. No treatment procedures were assigned or modified for research purposes.
Recipients underwent routine ICSI using donor oocytes previously vitrified at the MII stage. Six vitrified MII oocytes were allocated for warming. Oocytes lost during warming were not routinely replaced. No treatment procedures were assigned or modified for research purposes.
Live Birth Following the First Embryo Transfer per Initial Donor-Oocyte Allocation
Proportion of eligible recipient allocations resulting in at least one live-born infant following the first embryo transfer derived from the initial donor-oocyte allocation. The denominator includes all eligible allocations of six mature (MII) donor oocytes, including those resulting in no transferable embryo or no embryo transfer. Each allocation contributes a maximum of one successful outcome. Allocations without a first transfer or with unresolved birth outcomes at the data cutoff will be identified and handled according to the prespecified analysis plan.
Time frame: From initial donor-oocyte allocation through the pregnancy outcome of the first embryo transfer, assessed up to December 2027.
Mature Oocyte Availability for ICSI per Initial Allocation
Number of mature donor oocytes available for ICSI relative to the initial allocation of six MII oocytes. The measure captures quantitative loss before insemination and is compared between fresh and vitrified-warmed cohorts.
Time frame: From initial allocation to ICSI (Day 0).
Normal Fertilization Rate
Proportion of injected MII oocytes exhibiting normal fertilization (2PN). Calculated per oocyte injected by ICSI, with the number of 2PN embryos per initial allocation also assessed.
Time frame: Approximately 16-20 hours after ICSI (Day 1).
Usable Blastocyst Yield per Initial Oocyte Allocation
Number of usable blastocysts obtained from the initial donor-oocyte allocation, including allocations producing zero usable blastocysts. Usability is determined according to the participating laboratory's clinical criteria for transfer or cryopreservation.
Time frame: Within 5-7 days after ICSI.
Availability of at Least One Usable Blastocyst
Proportion of initial donor-oocyte allocations producing at least one usable blastocyst suitable for embryo transfer or cryopreservation. All eligible allocations remain in the denominator.
Time frame: Within 5-7 days after ICSI.
First Embryo Transfer Opportunity
Proportion of eligible initial donor-oocyte allocations resulting in at least one embryo transfer derived from the allocated oocytes within the prespecified follow-up period. Allocations without a transfer are retained in the denominator.
Time frame: From initial allocation through December 2027.
Cumulative Live Birth per Initial Oocyte Allocation
Proportion of eligible initial donor-oocyte allocations resulting in at least one live birth from any embryo transfer derived from that allocation within the prespecified follow-up period. Assessed in a cohort with sufficiently complete follow-up; allocations with unresolved outcomes will be identified and addressed in the analysis.
Time frame: From initial allocation through June 2028.
Plan to share: No — Individual participant data will not be publicly shared because the study uses retrospective clinical and laboratory records containing sensitive reproductive health information. Data access is subject to patient confidentiality, institutional policies, and applicable data protection regulations. Aggregated results will be reported in scientific publications.
No publications or documents are linked to this record.
Started Mar 2026 (actual). Primary completion is estimated for Dec 2027, 21 months after the start.
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From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is active, not recruiting, as verified in Oct 2026. You cannot join it, but the record below documents what was studied.
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Center for Reproductive Medicine Bocian