What is ICSI and why do it?
Injecting a sperm into an egg or Intracytoplasmic Sperm Injection (ICSI) is an assisted reproduction laboratory technique invented in1992. ICSI has given men with extremely poor sperm quality and low sperm count the ability to father children. Because sperm are injected directly into the egg, sperm that can't swim or can't bind to an egg are still able to fertilize an egg because these problems are bypassed.
Collection and Preparation of the Sperm
Sperm for ICSI is collected by either masturbation, electro-ejaculation or various surgical techniques. Sperm is processed in the lab to remove seminal fluid and cellular debris. Processed sperm is placed in droplets containing a thick liquid to slow down swimming sperm, allowing the technician to "catch" the sperm using a tiny, hollow, sharp glass needle called an injection pipette. The diameter of the injection pipette is barely wide enough to accommodate the sperm head, so that the sperm can be sucked up in the pipette and easily oriented head-first toward the egg. Prior to injection, the sperm must be immobilized by breaking the membrane behind the sperm head, without breaking off the sperm tail. This crucial step opens up the cell membrane and is essential for fertilization to occur once the sperm enters the egg.
Collection and Preparation of the Egg
Eggs are collected by a surgical procedure (transvaginal ultrasound-guided egg retrieval) under anesthesia in the operating room. When the egg is collected, it is enclosed in a cloud of cells (cumulus cells) which were needed for egg development and maturation but must be removed before sperm injection. Once the egg is free of cumulus cells, it is possible to visualize the structures around and within the egg. In preparation for fertilization, the mature egg expels a residual structure called a polar body, which contains an extra set of 23 chromosomes. Both the egg and discarded polar body are contained within a transparent shell called the zona pellucida.
Injecting the Sperm into the Egg
Sperm injection is performed using a specially outfitted microscope with joysticks operating hydraulically controlled syringes to transform the crude motions of the technician's hands into delicate microscopic movements. One syringe controls the injection pipette and the other the holding pipette. The holding pipette is a larger hollow glass needle with a smooth blunt end which can be used to pick up and manipulate the egg when gentle suction is applied. Rotating the egg so the polar body is at the 12 o'clock position identifies a safe injection zone on the egg. The injection pipette is used to suction up the immobilized sperm tail-end first. The sharp tip on the injection pipette breaches the zona pellucida and pierces the egg membrane, bringing the pipette inside the egg. The sperm is released from the pipette within the egg cytoplasm and the injection pipette is gently pulled from the egg, leaving the sperm behind. The egg is released from the holding pipette and moved to a drop of culture medium for continued development.
Fertilization Assessment: Did It Work?
The sperm is safely inside the egg, but the egg is not fertilized yet. Fertilization occurs when a cascade of biochemical and mechanical steps involving both sperm and egg bring maternal and paternal chromosomes together. The sperm head must open up to release its paternal chromosomes to be repackaged into a structure called a male pronucleus. Similarly, the egg has to produce a female pronucleus containing its maternal chromosomes. Male and female pronucleus merge in a process called syngamy and cell division begins. Visualizing the male and female nucleus inside the egg under the microscope confirms that fertilization is under way.
