Biopsy – collection of cells for testing from an organ or tissue. Embryo biopsy - collection of embryonic cells for testing. Usually cells for testing are taken from trophectoderm – future placenta. It is called trophectoderm biopsy.
Blastocyst – an embryo stadium on day 5. Due to natural selection in average every third normally fertilized egg develops up to blastocyst stadium. Not all embryos of good morphology on day 3 will develop to embryos of good morphology on day 5. Some of them will stop between day 3 and day 5. This is again the way natural selection works.
Under “good quality embryo” = “embryo of good morphology” we understand that the embryo’s looks under microscope correlates with a good chance to attach (based on follow up after many hundreds thousands of embryo transfers). Still good morphology does not guarantee that the embryo is genetically normal. In the age of 30 1 in 4 good in morphology blastocysts is abnormal, in the age of 41 3 in 4 good morphology blastocysts are abnormal. [Ata, Munne al 2012 – 875 cycles, 4600 embryos]
Chromosome aneuploidy – abnormal chromosome number. Normally humans have 46 chromosomes or 23 chromosome pairs: 22 pairs of similar non-gender chromosomes and 1 pair presented by two X chromosomes in females and by X an Y chromosomes in males
Euploid embryo – embryo with correct (normal) chromosome number. In human all somatic cells contain 23 chromosome pairs. 22 pairs are presented by non-gender chromosomes. The 23rd pair is presented by two X chromosomes in female and by chromosomes X and Y in males. Each of two chromosomes in each pair is received from an egg and a sperm, hence from a mother and a father. Not all embryos good in morphology are euploid.
Aneuploid embryo – an embryo with abnormal chromosome number. 90% of aneuploid embryos stop development very early and do not implant. Only 10 % of them can implant and result either in Biochemical pregnancy or in miscarriage under 12 weeks, or very seldom in life birth with Down syndrome. Some embryos of good morphology are aneuploid. Aneuploidy rate depends on the age of the egg. 1 in 4 morphologically good blastocysts is abnormal in the age of 30, 3 in 4 morphologically good blastocysts are abnormal in the age of 41.
PGS – preimplantation genetic screening
Single elective embryo transfer (SET) – transfer of only one embryo to the uterus, usually on day 5, selected on the basis of good morphology. Embryo chosen for SET has the best morphology and hence a potency to implant in comparison to the rest of the embryos produced from one egg collection. Still a good morphologically good embryo can be aneuploid with the risk of 20-30% in the age around 30 and risk of 70-80% in the age around 40. Additional screening of morphologically good embryos for 23 chromosome pairs helps not to use aneuploidy embryos and hence increases the efficiency of SET in all patients groups.
Biochemical pregnancy – pregnancy which has progressed to positive HCG test but not further
Clinical pregnancy – pregnancy confirmed by ultrasound
Implantation rates – amount of fetal sacs in the uterus per amount of transferred embryos
Implantation failure – no pregnancy after embryo transfer
Recurrent implantation failure – 3 or more fresh ETs without result