P-763 effect of duration of cryo-storage of vitrified embryos on obstetric and perinatal outcomes
Authors: Shibasaki S , Hattori H , Nakamura Y , Takahashi M , Aono N , Toya M , Igarashi H , Kyono K 
Published: June 2022

Abstract

Study question
Does the duration of cryo-storage of vitrified embryos affect obstetric and perinatal outcomes?

Summary answer
Duration of cryo-storage with an open vitrification system did not affect obstetric and perinatal outcomes.

What is known already
Frozen-thawed blastocyst transfer has been performed widely with improvement of embryo culture conditions and cryopreservation techniques. Although blastocyst vitrification has become an essential method to improve clinical outcomes of IVF, there has been little study into the relationship between a long duration of cryo-storage in liquid nitrogen and obstetric and perinatal outcomes.

Study design, size, duration
This retrospective study was conducted at Kyono ART Clinic from January 2007 to December 2020. This study includes a total of 1053 singletons derived from 2461 frozen-thawed blastocyst transfers in 2461 patients. Steel’s multiple comparison test was performed for clinical and perinatal outcomes with cases of cryo-storage of less than 3 months as a control group. P &lt; 0.05 was considered statistically significant.

Participants/materials, setting, methods
The subjects are patients who underwent their first single frozen-thawed blastocyst transfer (FBT) with an open vitrification system. Females &gt;40 years old at cryopreservation and those who underwent preimplantation genetic testing were excluded. According to cryo-storage duration, patients were grouped as follows: group A, 0-3 months (1255 cycles); group B, 3-6 months (1008 cycles); group C, 6-12 months (162 cycles), group D, 12-24 months (36 cycles).

Main results and the role of chance
Both the mean maternal age at blastocyst cryopreservation (A: 33.7±3.6, B: 34.1±3.5, C: 34.8±3.2, D: 35.1±3.3) and the mean maternal age at FBT (A: 33.8±3.6, B: 34.4±3.5, C: 35.5±3.1, D: 36.4±3.3) in groups B, C, and D were significantly higher compared to those in group A.. There was no significant difference in the survival rate after blastocyst thawing [A: 97.4% (1256/1290), B: 98.3% (1010/1027), C: 99.4% (163/164), D: 97.2% (35/36)]. The pregnancy rate in group C was significantly lower compared to group A [A: 60.0% (752/1254), B: 61.4% (619/1008), C: 48.1% (78/162), D: 63.9% (23/36)] The gestational age of group C was significantly lower compared to group A (A: 39.5±1.8, B: 39.4±1.8, C: 38.4±3.1, D: 39.8±1.6), but there were no significant differences in live birth weight or height. There were no significant differences in congenital abnormality rate [A: 1.3% (7/541), B: 2.5% (11/440), C: 1.8% (1/56), D: 0.0% (0/16)], placental abnormalities such as placenta previa [A: 1.3% (7/541), B: 1.6% (7/440), C: 1.8% (1/56), D: 0.0% (0/16)], perinatal abnormalities such as hypertensive disorders of pregnancy or gestational diabetes [A: 6.1% (33/541), B: 8.6% (38/440), C: 1.8% (1/56), D: 6.3% (1/16)] among the four groups.

Limitations, reasons for caution
We could not provide sufficient information on confounding factors such as smoking habits, and the sample size was too small for multivariate analysis. The safety of longer storage will need to be verified as this has not been clarified in this study.

Wider implications of the findings
The pregnancy rate in group C was significantly lower than that in group A, but the effect was small: 0.065, power of 0.78. Our data suggested that the duration of cryopreservation with an open vitrification system in liquid nitrogen did not affect obstetric or perinatal outcomes.

Trial registration number
not applicable