P-135 Clinical outcomes depending on post-warming culture duration of vitrified-warmed single blastocyst transfer cycles
Authors: Errazuriz J , Alwane E , Filselcker I , Durruty G , Sanhueza P , Gonzalez P , Donoso P 
Published: June 2022

Study question

What is the impact of post-warming blastocysts after very short-term culture (&lt;2 hours) or short-term culture (2–4 hours) on the clinical outcomes?

Summary answer

The clinical outcomes of very short-term culture and short-term culture were not significantly different in vitrified-warmed blastocyst transfer.

What is known already

In vitrified-warmed blastocyst transfer (VBT), complete blastomere survival and mitotic resumption during warming are generally considered to be the most important factors affecting pregnancy outcomes. It has been assumed that a sufficient warming time may be required for resumption of cell proliferation and development. Currently there is evidence that suggests a minimum mean time of 2.70 ± 1.20 necessary to complete the re-expansion of the embryo that allows evaluating its adequate development. However, the effect of culture duration on pregnancy outcomes in VBT remains controversial.

Study design, size, duration

A retrospective observational study was carried out, with all the patients who had frozen-thawed embryos transferred between January and December 202, in Clínica Alemana, Santiago, Chile. The average standard time for embryo thawing in our center is 2 hours. However, on certain occasions, due to its insufficient development and the pressing schedule of surgery rooms, a second embryo must be thawed, usually in less than 2 hours.

Participants/materials, setting, methods

Embryos were divided into two study groups depending on whether their post-warming culture period was very short-term (&lt;2 hours) or short-term culture (2–4 hours). Only transfers of 1 embryo on day 5-6 were included. Embryo morphology was analyzed with a Garner microscope score to estimate the quality of the embryos in both groups.

Main results and the role of chance

During the study period, a total of 127 single VBT cycles were included: 48 in the very short-term group and 79 in the short-term group. Patients’ demographic characteristics did not significantly differ between the groups. (Age 34.9±3.6 vs 35±3.4, p=0.89; Infertility duration (yr) 2.75±1.1 vs 2.5 ±1.1, p=0.24; AMH 2.1 [0.2-5.4] vs 2.1 [0.2-5], p=0.84) An analysis of previous fresh in vitro fertilization cycles and subsequent VBT cycle parameters revealed no differences in the number of retrieved oocytes (11.7 vs 12, p=0.74), the number of fertilized oocytes (8.6 vs 8.5, p=0.86), the number of vitrified blastocysts (3.4 vs 3.6, p=0.87) and in both groups. The clinical pregnancy rate per embryo transferred were similar in the very short-term culture group and the short-term culture group (66.7% vs. 68.4%, p=0.44). There was no significant difference in the ongoing pregnancy rate per embryo transferred between the two groups (18,8% vs. 16.5.%, p=0.74). The miscarriage rate in both groups was comparable (p=0.77).

Limitations, reasons for caution

The small number of women recruited ant the retrospective design of the study, should be recognized as possible sources of bias.

Wider implications of the findings

This study showed that the culture time after warming was irrelevant for blastocyst implantation potential, and that the speed of re-expansion was not correlated with clinical outcomes.

Embryo transfer timing after warming may be determined by optimizing each laboratory’s work flow.

Trial registration number

0