Assisted Reproductive Technology (ART) refers to medical procedures used to address infertility by handling eggs and sperm in a laboratory environment. The most common form is In Vitro Fertilization (IVF), which involves fertilizing an egg outside the body. IVF encompasses two distinct methods: conventional IVF and Intracytoplasmic Sperm Injection (ICSI). These techniques share preparatory steps but differ fundamentally at the moment of fertilization.
How Standard In Vitro Fertilization Works
Conventional IVF begins with ovarian stimulation, using injectable hormone medications to encourage the ovaries to produce multiple mature eggs in a single cycle. This process is monitored closely using ultrasound and blood tests to track the development of follicles. The goal is to retrieve more than the single egg that normally matures during a natural cycle.
Once follicles reach maturity, a final injection triggers the eggs’ final maturation. Approximately 36 hours later, the eggs are retrieved through transvaginal ovum retrieval. A needle, guided by ultrasound, is inserted through the vaginal wall to aspirate the fluid containing the eggs from the follicles.
In the laboratory, the retrieved eggs and a prepared sperm sample are placed together in a culture dish, known as co-incubation. This defining step of conventional IVF relies on the sperm’s innate ability to penetrate the egg’s outer layer and achieve fertilization on its own, mimicking natural conception. The embryologist monitors the dish, allowing the strongest sperm to naturally fertilize the egg over several hours.
Intracytoplasmic Sperm Injection: The Key Difference
Intracytoplasmic Sperm Injection (ICSI) is a specialized technique within the IVF cycle that completely bypasses the natural selection process. Instead of placing thousands of sperm with the egg, ICSI involves direct, manual intervention by an embryologist, requiring a specialized inverted microscope and ultrafine micromanipulation tools.
To perform ICSI, a single, morphologically normal and motile sperm is selected from the sample. Using a tiny, hollow glass needle called a micropipette, the embryologist immobilizes the sperm by gently touching its tail and draws it into the needle for injection.
The mature egg is held steady using a separate holding pipette. The injection needle containing the single sperm is inserted directly through the egg’s outer shell and into the cytoplasm. This physical delivery ensures fertilization, overcoming barriers that prevent natural penetration. The resulting fertilized egg is then cultured and transferred to the uterus as in conventional IVF.
Indications for Choosing ICSI
ICSI is primarily recommended to manage severe male factor infertility, such as extremely low sperm count (oligozoospermia) or poor sperm movement (asthenozoospermia). ICSI ensures fertilization even when sperm lack the numbers or motility required to penetrate the egg naturally. This technique is also necessary when sperm is surgically retrieved directly from the epididymis or testicle (e.g., TESA or PESA), as this sperm may not be fully functional for conventional fertilization.
ICSI is also utilized after poor or total fertilization failure in a previous conventional IVF cycle, even with a normal sperm sample. This suggests an issue with the sperm’s ability to activate or penetrate the egg. Furthermore, ICSI is routinely performed when Preimplantation Genetic Testing (PGT) is planned for the resulting embryos. The direct injection minimizes the risk of extraneous sperm contaminating the genetic sample, which could skew test results.
Success Rates and Procedural Risks
ICSI significantly increases the fertilization rate for eggs retrieved from couples with male factor infertility, often achieving 50% to 80% successful fertilization. Conventional IVF typically achieves a fertilization rate closer to 50%. However, once fertilization occurs, the subsequent success rates—the chances of achieving a clinical pregnancy and live birth per embryo transfer—are comparable between ICSI and conventional IVF.
Both procedures carry the same risks associated with ovarian stimulation and egg retrieval, such as ovarian hyperstimulation syndrome (OHSS) and multiple pregnancies. ICSI introduces an additional procedural risk, as the physical injection can damage the egg in about 5% to 15% of cases, rendering it unusable. Some studies suggest a slightly increased risk of certain congenital anomalies in ICSI-conceived children, particularly when male infertility is genetic. ICSI also increases the overall cost of the ART cycle due to the specialized equipment and highly skilled micromanipulation time required.