Table 8.

Main advantages and disadvantages of MRTs.

MRT	Advantages	Disadvantages
GVT	-Embryo generation not required -Germinal vesicle is large and easy to manipulate	-Very low efficacy (requires in vitro maturation) -Deficient growth in murine model
MST	-Embryo generation not required -Spindle has few surrounding mitochondrion (low carry-over) -Large number of articles with good results	-Meiotic spindle is hard to visualize (not surrounded by membrane) -Possibility of not transferring a chromosome disperse within the cytoplasm (frequent in elderly women’s oocytes) -Spindle is sensitive to micromanipulation (maturation premature activation)
PNT	-Pro-nuclei resist micromanipulation -Pro-nuclei are easily visible under the microscope (surrounded by membrane) -Large number of publications	-Generation and destruction of an embryo (donor zygote) -Carry-over rate depends on the operator (cytoplasm surrounding the pro-nucleus is rich in mitochondrion)
PB1T	-Embryo generation not required -Minimum carry-over -Easy manipulation of PB1 (isolated in a membrane) -Possible to combine with MST (saving maternal ovules)	-Possible epigenetic differences between PB1 and oocyte genomes ** -Lack of publications
PB2T	-Minimum carry-over -PB2 is easy to manipulate (isolated in a membrane) -Possible to combine with PNT (saving maternal ovules)	-Generation and destruction of an embryo (donor zygote) -Possible epigenetic differences between PB2 and oocyte genomes ** -Lack of publications -Poor efficacy: difficult to distinguish female pro-nucleus in human zygotes

** This disadvantage has been refuted by recent works [31,39], although further data will be required. MRT: mitochondrial replacement techniques. GVT: germinal vesicle transfer. MST: meiotic spindle transfer. PNT: pro-nucleus transfer. PB1T: first polar body transfer. PB2T: second polar body transfer.