Table 5.

The main oocyte and embryo biopsy approaches to conduct preimplantation genetic testing

	PB biopsy	Blastomere/cleavage-stage biopsy	Blastocyst/TE biopsy
Fragment origin	Waste products of maternal meiosis	Totipotent cells	TE gives origin to the placenta and the extraembryonic membranes
Number of cells 2 (both required) retrieved		Two might be “one” retrieved, but it is discouraged	5-10 trophectoderm cells
Complexity in the acquisition of the skill	Day 0+ day 1 approach	Moderate	Day 3 hatching-based strategy: Low-to-moderate
	Moderate
	Day 1 only approach		Morula hatching-based strategy: Low to moderate
			Same day hatching-based strategy: Low to moderate
	Moderate to high (PB1 and PB2 should be reliably recognized)	Simultaneous ZP opening and TE cells retrieval strategy: Moderate to high
Complexity in the performance of tubing	Moderate to high	Moderate	Moderate to high
Embryo developmental competence	Unpredictable at this stage	Unpredictable at this stage	Only embryos developing to the blastocyst stage are biopsied
Laboratory workload	High (all oocytes/zygotes should be biopsied regardless of their developmental competence)	Moderate (all oocytes/zygotes/cleavage-stage embryos should be biopsied regardless of their developmental competence)	Multiple time slots required (day 5-7) and cryopreservation mostly mandatory
			Day 3 hatching-based strategy: Moderate to high (all embryos should undergo ZP opening at the cleavage stage regardless of their developmental competence)
			Morula hatching-based strategy: Moderate to high (all morulae should undergo ZP opening regardless of their developmental competence)
			Same day hatching-based strategy: Moderate to high (all blastocysts should undergo ZP opening and monitoring of TE cells hatching)
			Simultaneous ZP opening and TE cells retrieval strategy: Moderate
Extended embryo culture	Suggested but not mandatory	Suggested but not mandatory	Not mandatory
Cryopreservation following biopsy	According to laboratory policy	According to laboratory policy	Mostly mandatory
Meiotic errors assessed	Only maternal	Yes	Yes
Mitotic errors assessed	Not	Not	Possible within given technical, methodological, and biological limitations (e.g., molecular platform and bioinformatic parameters - dependent, inevitable sampling bias)
Inconclusive diagnosis (%)	10	10	<10
Impact on reproductive competence	Not reported, but more data are still required	Reduced implantation potential post biopsy	Not reported, but more data are still required

The parameters “low,” “moderate,” and “high” were agreed unanimously after a thorough discussion among all the components of the working group. TE=Trophectoderm, PB=Polar body, ZP=Zona pellucida