P-234 The internal temperature of the catheter during the transfer: potential effects on the embryonic microenvironment
Authors: Scarica C , Moreno S , Barbarulo F , Bianco C , Carconi G , Sanchez M , Gardini F , Monaco A 
Published: July 2024

Abstract

Study question
Do the external environment and the different loading procedures affect temperature in the transfer catheter and embryo development during embryo transfer?

Summary answer
The inner temperature of transfer catheter dropped during the embryo transfer. Mouse 2-cell-embryos exposed to the transfer showed lower blastocyst and hatching rates.

What is known already
Embryo transfer is a crucial process composed of complex phases, which start from embryo loading into the catheter, and culminate in the transfer room in an open environment at room temperature. Although the transfer technique has been refined over time and several adjustments have been proposed towards its standardization (ASRM, 2017, D’Angelo et al., 2022), there is still great variability (Cirillo et al 2020). Few literature data are available regarding possible influences of the external environment on inner catheter conditions. Only recently, temperature drop during transfer has been described (Macklon et al 2021).

Study design, size, duration
We addressed possible temperature variations to which the embryo is exposed during transfer, by using a thin temperature probe placed inside a catheter. We simulated a total of 120 transfers (60 transfers with “fluid only” methodology and 60 with “air-fluid”). Additionally, we performed Mouse Embryo Assay (MEA) during transfer simulations and then cultured up to blastocyst to assess any impact of temperature drop exposure during transfer

Participants/materials, setting, methods
120 mock transfers were performed, recording the temperature in the inner catheter were the embryos are loaded. In our setting, the procedure lasts 60-100 seconds. The internal temperature of the catheter was recorded after 15 min of preheating, at the loading and in the following 60 seconds. Environmental temperature and humidity values were recorded. A total of 73 mouse embryo were used for MEA (39 exposed to catheter, 34 controls) and cultured in time-lapse

Main results and the role of chance
The 120 simulations took place at an average environmental temperature of 22.43 °C± 0.85, and a relative humidity of 57.4%± 5.1. After 15 min of preheating the empty catheter reached an average temperature of 33.04 °C ±2.08. Upon loading, the average temperature inside the catheter was 31.22 °C± 1.67 and after 60 seconds, it dropped to 29.15 °C ±1.88. The comparison between the “fluid only” and “air-fluid” shows the following results: internal temperature at “fluid only” loading 31.97 °C ± 1.87, “air-fluid” 30.11 °C ± 1.48 (p &lt; 0.001); Average temperature after 60 seconds “fluid only” 29.98 °C ± 1.71, “air-fluid” 27.91 °C ± 1.38 (p &lt; 0.001). Seventy-three 2-cells mouse embryos were thawed and used to perform MEA tests. 39 of them were exposed to 5 transfer simulations of 200 seconds, and then put in culture in time-lapse incubator (single step medium, 6% CO2, 5%O2). The blastocyst rate was 82% in the control group and 74% in the exposed group (X2 (1, N = 73) = 0.6783, p &gt;0.05). Hatching rate significantly differed (61% in controls vs. 34% in the exposed (X2 (1, N = 57) = 3.9, p = 0.04). Morphokinetics were not different among groups

Limitations, reasons for caution
The monocentric nature of this pilot study can represent the limitation of the single environmental conditions at which the catheters are exposed during the embryo transfer

Wider implications of the findings
The transfer procedure exposes embryos to a drastic decrease in temperature, directly proportional to the execution time. Mouse embryos showed an impaired development after being exposed to transfer simulations. Novel strategies to stabilize temperature during embryo transfer are needed.

Trial registration number
non-clinical trial