A sperm can fertilize a woman’s egg, the head of the sperm must attach to the outside of the egg, and the sperm then pushes through the outer layer to the inside of the egg where fertilization takes place.
Sometimes the sperm cannot penetrate the outer layer, for a variety of reasons. The egg’s outer layer may be thick or hard to penetrate or the sperm may be unable to swim. In these cases, a procedure called intracytoplasmic sperm injection (ICSI) can be done along with in vitro fertilization (IVF) to help fertilize the egg. During ICSI, a single sperm is injected directly into the cytoplasm of the egg.
Fertilization occurs when one of the sperm enters the cytoplasm of the egg. In the ICSI process, a tiny needle, called a micropipette, is used to inject a single sperm into the center of the egg. With either traditional IVF or ICSI, once fertilization occurs, the fertilized egg (now called an embryo) grows in a laboratory for 1 to 5 days before it is transferred to the woman’s uterus. ICSI fertilizes 50% to 80% of eggs.
ICSI helps to overcome fertility problems, such as:
- The male partner produces too few sperm to do artificial insemination (intrauterine insemination [IUI]) or IVF.
- The sperm may have reduced motility.
- The sperm may have poor morphology.
- A blockage in the male reproductive tract may keep sperm from getting out.
- Failed fertilization with traditional IVF in the previous cycle.
- Previously frozen eggs are being used
The chance of birth defects associated with ICSI is similar to IVF but slightly higher than in natural conception. The slightly higher risk of birth defects may actually be due to infertility and not the treatments used to overcome infertility.