P–515 Clinical outcome of mosaic-blastocyst transfer versus euploid-blastocyst transfer in single frozen blastocyst transfer cycles
Authors: Yap W Y , Lim M W , Lee C S S 
Published: August 2021

Abstract

Study question
What is the clinical outcome of transferring a mosaic blastocyst versus a euploid blastocyst in single frozen blastocyst transfer (sFBT) cycles?

Summary answer
Single mosaic blastocyst transfer has similar clinical outcome to single euploid blastocyst transfer.

What is known already
Embryonic mosaicism occurs when there are two or more distinct cell lines found in preimplantation embryos derived from IVF. Data from recent studies show that mosaic blastocysts have the potential to implant and can result in healthy live births. As a result, patients now have the option of transferring mosaic blastocyst when they do not have any euploid blastocyst available for transfer. However, the clinical outcome of transferring mosaic blastocyst has not been definitively reported. Thus, a retrospective study was conducted to compare the clinical outcome of mosaic sFBT and euploid sFBT.

Study design, size, duration
A total of 602 patients underwent frozen blastocyst transfer in Alpha IVF from January to October 2019 and had their blastocysts screened for aneuploidy. These patients were divided into 2 groups: 26 patients with mosaic blastocysts transferred (Group A, age ranged 19–44), and 576 patients with euploid blastocysts transferred (Group B, age ranged 21–44). The mean age of patients from Group A and B were 34.0 and 32.8 respectively (p &gt; 0.05).

Participants/materials, setting, methods
All samples had their DNA libraries constructed for sequencing using Next Generation Sequencing according to manufacturer’s specification (IonTorrent, USA). All blastocysts were frozen for subsequent sFBT cycle (Cryotech, Japan). All thawed blastocysts for sFBT survived with morphologically intact inner cell mass and trophectoderm cells. The importance of antenatal confirmation of the fetal chromosome status was emphasized in patients from Group A. The clinical outcomes of both groups were analysed and compared.

Main results and the role of chance
No significant differences were seen in the clinical pregnancy and implantation rate of Group A and B (65.4% vs 63.0%; p &gt; 0.05). The miscarriage rate of Group A and B were 23.5% and 14.0% respectively. Albeit the higher miscarriage rate in Group A, there was no statistical significance between these two groups (p &gt; 0.05).
Group A was further divided into two subgroups, Subgroup A1: low risk mosaic blastocyst transfer; Subgroup A2: high risk mosaic blastocyst transfer. In the comparison of Group A subgroups, the clinical pregnancy and implantation of Group A1 is higher than Group A2 (76.9% vs 44.4%). In addition, the miscarriage rate of Group A1 and A2 were 23.1% and 0.0% respectively. Interestingly, there was no statistical significance in clinical pregnancy rate, implantation rate and miscarriage rate between these two subgroups.

Limitations, reasons for caution
This is a retrospective study and the sample size was comparatively smaller in the mosaic blastocyst transfer group than the euploid blastocyst transfer group. Further studies with a larger sample size should be carried out to ascertain the clinical outcome.
Wider implications of the findings: Single mosaic blastocyst transfer has similar clinical outcome to single euploid blastocyst transfer. Thus, mosaic blastocyst can be considered for transfer when no euploid blastocyst are available. Nevertheless, stringent antenatal surveillance for chromosomal abnormalities to confirm the chromosomal status of the fetus must be followed.

Trial registration number
Not applicable