Selection of the embryo to be transferred is very important. There is a close relationship between pregnancy rates and the transferred embryo number and quality.

Above all, it depends on the number and the quality of the eggs collected from the patient. The main reason for better pregnancy results in young patients is this. With declining age the number and the quality of the collected eggs decrease.

Chromosome defects in the eggs effects the development of the embryo negatively. With declining age, the risk of having chromosome defects in embryo increases.

The technical hardware of the test tube baby centre, liquids and media used, the conditions of the laboratory and the incubator, hygienic conditions.

The knowledge and experience of the embryologist and biologists working in the laboratory.

The size of the blastomers establishing the embryo and their shapes’ being symmetrical

Percentage of the fragments in the embryo (fragmentation)

Grade I: Blastomers are of equal size, fragmentation is not present or < 20%

Grade II: Blastomers of unequal sizes, fragmentation is not present or < 20%

Grade III : Fragmentation 20-50% and/or nonhomogenous cytoplasm and /or multi-nuclear blastomers.

Grade IV: Fragmentation > 50%

Today, embryo transfers are usually performed on the 3rd day following the egg collection process. On this 3rd day, when grade 1 and 8 celled embryo is transferred, the best pregnancy results are obtained.