Effective protection: the embryonic development and clinical outcomes of emergency vitrification of 1246 oocytes and Day 0–Day 5 embryos in a natural disaster
Authors: Song Wenyan , Zhang Fuli , Wang Yuan , Shi Hao , Sun Ning , Jin Haixia , Wang Xiaopeng , Guo Yihong , Hu Linli , Zhai Jun , Dai Shanjun , Zhang Yile , Su Yingchun , Yao Guidong , Shi Senlin , Wen Shuang , Song Ning , Wu Zhaoting , Chen Lei , Cheng Tingting , Kang Beijia , Sun Jing , Huang Xianju , Sun Zhimin , Cheng Luyao , Liang Yuling , Sun Yingpu 
Published: October 2023

Abstract

STUDY QUESTION
Can emergency vitrification protect embryos and oocytes during natural disasters or other events that prevent normal practice to achieve satisfactory embryonic development and clinical outcomes at a later time?

SUMMARY ANSWER
Emergency vitrification of oocytes and Day 0–Day 5 (D0–D5) embryos during disasters is a safe and effective protective measure.

WHAT IS KNOWN ALREADY
When some destructive events such as floods, earthquakes, tsunamis, and other accidents occur, emergency vitrification in embryo laboratories to protect human embryos, oocytes, and sperm is one of the important measures of an IVF emergency plan. However, there are few detailed reports on emergency vitrification in a state of disaster, especially about oocytes and D0 zygotes. Therefore, the effectiveness and safety of emergency vitrification of oocytes and D0–D5 embryos in disaster states are still unclear.

STUDY DESIGN, SIZE, DURATION
A retrospective study was made in the Reproductive Medicine Center of the First Affiliated Hospital of Zhengzhou University from January 2018 to November 2022. The record rainstorms in Zhengzhou, China, caused severe flooding, traffic disruptions, and power outages. From 17:30, 20 July 2021 to 17:30, 21 July 2021, 1246 oocytes and D0–D5 embryos of 155 patients were vitrified whilst the laboratory had only an emergency power supply.

PARTICIPANTS/MATERIALS, SETTING, METHODS
As of 21 December 2021, 1149 emergency vitrified oocytes and D0–D5 embryos of 124 patients underwent frozen-thawed embryo transfer (FET). They were divided into the following four groups according to the days of embryo culture in vitro: oocyte group, Day 0–Day 1 (D0–D1) group, Day 2–Day 3 (D2–D3) group, and Day 4–Day 5 (D4–D5) group. Control groups for each were selected from fresh cycle patients who underwent IVF/ICSI from January 2018 to October 2021. Control and emergency vitrification patients were matched on criteria that included age, fertilization method, days of embryonic development, and number and grade of transferred embryos. A total of 493 control patients were randomly selected from the eligible patients and matched with the emergency vitrification groups in a ratio of 4:1. The results of assisted reproduction and follow-up of pregnancy were analyzed. The embryonic development, clinical outcomes, and birth outcomes in each group were statistically analyzed.

MAIN RESULTS AND THE ROLE OF CHANCE
A significant difference was observed in fertilization rate (81% versus 72%, P = 0.022) between the oocyte group and the control group. Significant differences were also observed in the monozygotic twin pregnancy rate (10% versus 0%, P = 0.038) and ectopic pregnancy rate (5% versus 0%, P = 0.039) between the D0–D1 group and the control group. No significant differences (P &gt; 0.05) were observed between vitrified oocytes/D0–D1 embryos/D2–D3 embryos and the control group on the number of high-quality embryos (3.17 ± 3.00 versus 3.84 ± 3.01, P = 0.346; 5.04 ± 3.66 versus 4.56 ± 2.87, P = 0.346; 4.85 ± 5.36 versus 5.04 ± 4.64, P = 0.839), the number of usable blastocysts (1.22 ± 1.78 versus 1.21 ± 2.03, P = 0.981; 2.16 ± 2.26 versus 1.55 ± 2.08, P = 0.090; 2.82 ± 3.23 versus 2.58 ± 3.32, P = 0.706), clinical pregnancy rate (56% versus 57%, P = 0.915; 55% versus 55%, P = 1.000; 40% versus 50%, P = 0.488), miscarriage rate (30% versus 15%, P = 0.496; 5% versus 11%, P = 0.678; 17% versus 20%, P = 1.000), and live birth rate (39% versus 49%, P = 0.460; 53% versus 50%, P = 0.772; 33% versus 40%, P = 0.635). No significant differences (P &gt; 0.05) were observed between the D4–D5 group and the control group on clinical pregnancy rate (40% versus 55%, P = 0.645), miscarriage rate (0% versus 18%, P = 1.000), and live birth rate (40% versus 45%, P = 1.000)

LIMITATIONS, REASONS FOR CAUTION
The retrospective study design is a limitation. The timing and extent of natural disasters are unpredictable, so the sample size of vitrified oocytes, zygotes, and embryos is beyond experimental control.

WIDER IMPLICATIONS OF THE FINDINGS
This study is the first study analyzing embryonic development, clinical outcomes, and birth outcomes of large samples of oocytes, D0 zygotes, and D1–D5 embryos after emergency vitrification under the disaster conditions. The results show that emergency vitrification is a safe and effective protective measure applicable to oocytes and D0–D5 embryos. The embryology laboratories need to be equipped with an emergency uninterrupted power supply capable of delivering for 6–8 h at full load.

STUDY FUNDING/COMPETING INTEREST(S)
This work was supported by the National Natural Science Foundation of China (grant 81871206). The authors declare that they have no conflicts of interest. All authors have completed the ICMJE Disclosure form.

TRIAL REGISTRATION NUMBER
N/A.