IntraCytoplasmic sperm injection (ICSI) is the most recent development
in the field of assisted fertilization. The first pregnancy from
any of the assisted fertilization techniques was reported in 1988,
and resulted from partial zona dissection (PZD) in which a small
incision or tear was made in the shell (zona pellucida) of the
egg to aid access for sperm. These defects in the zona pellucida
of the eggs were associated with a high number of polyspermic
embryos (eggs fertilized with more than one sperm, therefore abnormal
and not viable). Also in 1988 the first pregnancy from subzonal
insertion of sperm (SUZI) was reported. In the SUZI procedure
several sperm are placed into the perivitteline space between
the outer shell of the egg (zona pellucida) and the plasma membrane
of the egg. It was not until 1992 that the initial pregnancies
with ICSI were reported, yet since that time this technique has
overwhelmed the field of assisted fertilization.
The history of ICSI is interesting and shows how long it takes
for medical advances to decome clinically available even in the
most successful of situations.
In 1976, researchers reported that the injection of whole spermatozoa
into hamster eggs resulted in the transformation of the sperm's
nucleus into the male pronucleus. This illustrated that whole
mature sperm can be microsurgically injected into the cytoplasm
of eggs and the genetic material within the chromosomes (DNA)
will organize into the normal structure (the male pronucleus).
This important discovery allowed for the development of ICSI in
humans.
In 1988, researchers first reported the finding that microinjection
of human spermatozoa into human oocytes resulted in pronuclear
formation. This confirmation that a similar procedure with human
material resulted in a similar outcome occurred some 13 years
after the initial hamster finding.
In 1992 the first pregnancies following intracytoplasmic injection
of single spermatozoon into an oocyte were reported.
In 1997, ICSI has about a 60-80% fertilization rate per egg with
an overall "take home baby" rate that compare nicely
to rates of standard IVF performed for couples without a male
factor.
This success for ICSI is incredible since the only criterion required
for the sperm is that they are alive. Live sperm can be most easily
detected by their motility but even nonmotile live sperm or immature
sperm from testicular biopsy has been used successfully with ICSI.
This is because the sperm do not have to accomplish fertilization
on their own, rather, they are placed directly into the egg's
cytoplasm.
Related Topics: Sperm
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