Design:
Retrospective study.
Sim PK, Tham MY, Sivasengaran S, Nadkarni P. Live Birth Rate from Human Oocyte Vitrification Using Cryotop Method. Poster presented at the MACE (Malaysian Assisted Conception and Embryology) Conference, 2017. KL Fertility & Gynaecology Centre, Kuala Lumpur, Malaysia.
Presented: MACE Conference, 2017 | Last reviewed: August 2026
This page summarises findings from a conference poster presentation based on clinical data from KL Fertility & Gynaecology Centre. It is presented here for the clinical and scientific community and is not intended as a substitute for individualised patient counselling.
Funding and disclosures: No funding declarations are available for this conference poster. The authors report no competing interests.
Background and Aim
Human oocyte cryopreservation with vitrification has become the primary technology for oocyte banking in modern IVF practice, replacing slow-freezing due to substantially higher post-warming survival rates. The Cryotop method, developed by Kuwayama et al., is a carrier-based vitrification system that achieves ultra-rapid cooling by loading oocytes onto an open-pulled polypropylene strip that is plunged directly into liquid nitrogen, minimising ice crystal formation.
The clinical applications of oocyte vitrification are broad. They include fertility preservation for women facing gonadotoxic cancer treatment, fertility banking for women who wish to delay motherhood, management of cycles where male partners are unable to produce a sperm sample on the day of egg collection, and provision of oocyte banking programmes in jurisdictions where embryo cryopreservation is restricted for legal or religious reasons.
Although theoretical concerns have been raised about potential chromosome misalignment during vitrification due to disruption of the meiotic spindle, high clinical pregnancy and live birth rates have been reported following transfer of embryos derived from vitrified/thawed oocytes in multiple published series. The aim of this study was to examine whether pregnancy rate and live birth rate are affected by oocyte vitrification using the Cryotop method at KL Fertility & Gynaecology Centre.
Method: Study Design and Patient Population
Subjects:
34 patients who had embryos generated from oocyte vitrification between June 2011 and September 2017 at KL Fertility & Gynaecology Centre.
Vitrification method:
Cryotop method. All surviving Metaphase II (MII) oocytes were inseminated by intracytoplasmic sperm injection (ICSI).
Embryo transfer timing:
Transfers were performed on Day 2, Day 3, or Day 5.
Primary endpoint:
Live birth rate (LBR), defined as the number of deliveries resulting in at least one live birth divided by the total number of patients.
Results: Survival, Fertilisation, Pregnancy, and Live Birth Rates
Table 1. Oocyte vitrification outcomes using the Cryotop method (n=34 patients)
Outcome | Result |
|---|---|
Total oocytes vitrified | 261 |
Oocytes survived warming | 227/261 (87.0%) |
Oocytes fertilised (of survived) | 149/227 (65.6%) |
Average embryos transferred per patient | 1.7 |
Pregnancies achieved | 17/34 (50.0%) |
Deliveries | 11/34 (32.4%) |
Babies born (healthy) | 12 (10 singletons, 1 set of twins) |
An oocyte survival rate of 87.0% (227/261) and a fertilisation rate of 65.6% (149/227) were achieved following warming. A total of 17 pregnancies were obtained from 34 patients, giving a pregnancy rate of 50.0% per patient. Eleven of these 17 pregnancies resulted in delivery, giving a live birth rate of 32.4% per patient. Twelve healthy babies were born from the 11 deliveries: 10 singletons and one set of twins.
Discussion: How These Findings Compare With Published Evidence
The results from this study are consistent with benchmarks established in published literature on oocyte vitrification using the Cryotop method:
- The 87.0% oocyte survival rate is somewhat below the highest benchmarks reported in contemporary series, where post-warming survival rates of 90-99% have been reported with the Cryotop method, particularly in oocyte donation programmes. A 2024 15-year follow-up series noted that many publications now report survival rates above 90%, attributed to advances in vitrification and warming protocols since the technique was first introduced.
- The 65.6% fertilisation rate of warmed oocytes is within the broadly reported range for ICSI of vitrified oocytes. Published series have reported fertilisation rates of approximately 65-80% depending on oocyte cohort characteristics, patient age, and sperm quality.
- The 32.4% live birth rate per patient is within the range reported in the literature for clinical (non-donor) oocyte vitrification programmes. A 2021 ASRM guideline on evidence-based outcomes after oocyte cryopreservation documented live birth rates of 17-39% per transfer cycle across published studies, with variation attributable primarily to the number of MII oocytes warmed and patient age at cryopreservation.
- The 50.0% pregnancy rate per patient is notably higher than the 32.4% live birth rate, reflecting pregnancy loss between implantation and delivery, which is consistent with published miscarriage rates following oocyte vitrification.
- A 2025 retrospective cohort study comparing fresh and vitrified donor oocyte cycles reported oocyte survival of 96% and live birth rates after the first embryo transfer of approximately 59% for both groups. The lower live birth rate in the present study (32.4%) is consistent with the expectation that non-donor, patient oocyte cohorts, with typically older and more heterogeneous oocyte quality, perform less well than donor oocyte programmes.
This study’s timeframe (2011-2017) spans the period during which oocyte vitrification was transitioning from an experimental technique to standard clinical practice in Malaysia. The results support the Cryotop method as an effective approach for oocyte cryopreservation that can achieve clinically meaningful pregnancy and live birth rates.
Clinical Significance
These findings confirm that human oocyte vitrification using the Cryotop method is a clinically effective technique that can result in healthy live births. The key practical implications are:
- Oocyte vitrification is a viable option for a wide range of indications including fertility preservation for cancer patients, social egg freezing, management of cycle contingencies (e.g. failure of sperm production on egg collection day), and oocyte banking in settings where embryo cryopreservation is restricted.
- An 87.0% survival rate and 32.4% live birth rate per patient are clinically meaningful outcomes, acknowledging that per-patient LBR is influenced by the number of oocytes available, their quality, and patient characteristics.
- The birth of 12 healthy babies from this cohort provides direct safety reassurance for the use of Cryotop vitrification in this centre's specific clinical context.
- Patients considering oocyte vitrification for fertility preservation should be counselled that per-cycle live birth rates depend substantially on the number of mature oocytes cryopreserved and on age at cryopreservation, factors this study was not designed to model individually.
Limitations of This Case Report
- Small sample size: only 34 patients, limiting statistical precision and precluding subgroup analysis by age, indication for vitrification, oocyte number, or embryo transfer day.
- The study spans a relatively long period (June 2011 to September 2017) during which vitrification protocols, warming solutions, and laboratory practices likely evolved. Pooling outcomes across this period may mask improvements over time.
- Embryo transfers were performed on Day 2, 3, or 5 without stratification in the reported results, making it impossible to assess whether transfer day influenced outcomes.
- No data on patient age, indication for oocyte vitrification, number of oocytes warmed per patient, or embryo quality are reported.
- Live birth rate is reported per patient, not per oocyte warmed or per embryo transferred. These different denominators yield substantially different rates and are not directly comparable across publications without knowing which denominator is used.
- Conference poster format; findings have not been subject to full peer-review.
Key Findings
- In 34 patients undergoing oocyte vitrification using the Cryotop method (June 2011 to September 2017), oocyte survival rate was 87.0% (227/261) and fertilisation rate was 65.6% (149/227).
- Pregnancy rate was 50.0% per patient (17/34); live birth rate was 32.4% per patient (11/34).
- Twelve healthy babies were born: 10 singletons and one set of twins.
- These results are consistent with published benchmarks for Cryotop oocyte vitrification in non-donor patient cohorts.
- The findings support oocyte vitrification using the Cryotop method as a clinically effective technique for fertility preservation and oocyte banking.
About the Team Behind This Case Report
- Poo Keen Sim is the Chief Embryologist and a member of the Scientific Team at KL Fertility & Gynaecology Centre, with over 20 years of hands-on experience in clinical embryology. She holds a Master's degree in Clinical Embryology and is a co-author of this study.
- Jasmine Tham Mei Yeong is a Senior Embryologist who has been with the KL Fertility Centre embryology team for over 10 years and has been involved in training embryologists both internally and from external centres. (Profile: Malaysian Society of Assisted Reproductive Technology)
- S. Sivasengaran conducted this research as part of the Embryology team at KL Fertility & Gynaecology Centre.
- Dato' Dr. Prashant Nadkarni is a Fertility Specialist in Reproductive Medicine at KL Fertility & Gynaecology Centre.
References
- Sim PK, Tham MY, Sivasengaran S, Nadkarni P. Live Birth Rate from Human Oocyte Vitrification Using Cryotop Method. Poster presented at the MACE Conference, 2017.
- Potdar N, Gelbaya TA, Nardo LG. Oocyte vitrification in the 21st century and post-warming fertility outcomes: a systematic review and meta-analysis. Reprod Biomed Online 2014;29:159-176. https://doi.org/10.1016/j.rbmo.2014.04.010
- Practice Committee of the American Society for Reproductive Medicine. Evidence-based outcomes after oocyte cryopreservation for donor oocyte in vitro fertilization and planned oocyte cryopreservation: a guideline. Fertil Steril 2021;116(1):36-47. https://doi.org/10.1016/j.fertnstert.2021.04.007
- Clinical outcomes of vitrified-warmed autologous oocyte cycles with 15-year follow-up at a single UK centre. Reprod Biomed Online 2024. https://doi.org/10.1016/j.rbmo.2024.103980
- Kuwayama M. Highly efficient vitrification for cryopreservation of human oocytes and embryos: the Cryotop method. Theriogenology 2007;67(1):73-80. https://doi.org/10.1016/j.theriogenology.2006.09.014