Embryology is the science of embryo development, which occurs from fertilization of the egg to the fetus stage. The term embryo refers to a tiny ball of dividing cells from the moment the fertilized egg implants into the uterus wall until the end of the 8th week after initial conception. After the 8th week, which is the 10th week of pregnancy, the developing human is called a fetus.
Intracytoplasmic Sperm Injection (ICSI)
Intracytoplasmic sperm injection is a procedure where a single sperm cell is injected directly into each egg to fertilize it. This procedure is used when male factor infertility is an issue, such as low sperm count, problems with sperm movement (motility), and abnormal sperm shapes.
ICSI is often chosen after previous fertilization failure. This technique can also be used for men who have had a previous vasectomy, or when vasectomy reversal was not successful. ICSI is a good choice for couples in which the man has suffered injury to the spina cord (affects erection) and for men with poor quality sperm.
Laser Selective Assisted Hatching
Laser selective assisted hatching is a procedure involving making a tiny hole in the tough outer layer of the embryo (zona pellucida). This is done to allow the embryo to properly emerge (hatch) from the shell to implant into the uterine lining (endometrium). The zona pellucida often undergoes changes that interfere with hatching.
Factors that affect hatching include advanced reproductive age, diminished egg quality, in vitro culture conditions, and diminished embryo quality related to severe fragmentation of cells. The embryologist performs assisted hatching using a tiny laser beam, and it is done right before embryo transfer.
Also called extended culture, blastocyst culture involves allowing the embryo to reach a more advanced development stage. Most human embryos are transferred on day three, called day-3 embryos. A blastocyst is a day-5 embryo. Normal developing embryos at day 4-6 have gene information that can be evaluated before the transfer.
Blastocyst culture allows the embryologist to determine which embryos are more likely to survive, and which embryos have genetic problems. Allowing the embryos to further develop also reduces the risk of multiple pregnancies, as blastocysts have higher implantation potential.
Preimplantation Genetic Screening (PGS)
Preimplantation genetic screening, also called embryo screening, is a sophisticated form of technology that allows the specialist to examine embryos for chromosome problems. Anomalies of chromosomes include single gene defects, structural chromosome anomalies (translocations), and numerical anomalies (aneuploidies). PGS allows embryo selection to increase chances of carrying the baby to term.
The highly controversial technique known as family balancing is a form of gender selection. New procedures now allow the embryologist to transfer embryos that are male or female. Gender selection is confirmed by analysis of the sex chromosomes in the embryo’s cells.
Cryopreservation of embryos involves preserving embryos at sub-zero temperatures. This form of embryo freezing is called vitrification, which has the greatest success rates regarding the thawing process and implantation. Embryo cryopreservation is an option for couples who have several embryos remaining after IVF who wish to attempt later cycles. Many couples who achieve pregnancy donate embryos for other couples use.