Infertility, defined by the World Health Organization (WHO) as the inability to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse, affects many individuals and couples globally. This challenge often leads to exploring assisted reproductive technologies (ARTs), medical procedures designed to help overcome biological or medical barriers to conception. Intracytoplasmic Sperm Injection (ICSI) represents a significant advancement within modern fertility treatments.
Understanding Intracytoplasmic Sperm Injection
Intracytoplasmic Sperm Injection (ICSI) is a specialized laboratory procedure performed as part of in vitro fertilization (IVF) that directly addresses fertilization challenges. An embryologist uses a tiny needle (micropipette) to inject a single sperm directly into the cytoplasm, the gel-like substance within a mature egg. This precise, microscopic intervention bypasses the natural process where sperm must navigate to and penetrate the egg’s outer layers.
This direct injection method differs from conventional IVF, where thousands of sperm are placed in a culture dish with an egg, and fertilization occurs spontaneously. In conventional IVF, sperm must swim to the egg, bind to its outer coating (zona pellucida), penetrate it, and then merge with the egg’s membrane to fertilize it. ICSI, by contrast, removes these natural barriers, ensuring a direct encounter between one selected sperm and one egg.
When ICSI is Recommended
ICSI is commonly recommended for specific infertility scenarios, particularly those involving male reproductive factors. It is frequently employed when there is a very low sperm count (oligozoospermia) or a complete absence of sperm in the ejaculate (azoospermia). Additionally, ICSI is beneficial for cases with poor sperm motility, where sperm struggle to swim effectively, or abnormal sperm morphology. For men with azoospermia, sperm can often be surgically retrieved directly from the testes or epididymis using techniques like testicular sperm aspiration (TESA) or percutaneous epididymal sperm aspiration (PESA).
Beyond male factor infertility, ICSI may also be advised in other situations. Couples who have experienced previous failed fertilization attempts with conventional IVF, where few or none of the eggs fertilized, often benefit from ICSI. It is also considered when using cryopreserved (frozen) eggs, as the freezing and thawing process can sometimes make the egg’s outer layer more difficult for sperm to penetrate naturally. Furthermore, ICSI can be a choice for cases of unexplained infertility or when preimplantation genetic testing (PGT) of embryos is planned, as it helps prevent contamination of the embryo biopsy by extraneous sperm.
The ICSI Process
The ICSI procedure begins with the female partner undergoing ovarian stimulation, typically involving daily hormonal injections for about 10 to 14 days to produce multiple mature eggs. Regular ultrasounds and blood tests monitor the growth of follicles, the fluid-filled sacs containing the eggs, and hormone levels. Once the follicles reach an optimal size, a “trigger shot” of hCG hormone is administered to induce the final maturation of the eggs.
Approximately 34 to 36 hours after the trigger shot, egg retrieval is performed, a minimally invasive, ultrasound-guided procedure where a needle collects the mature eggs from the ovaries. Simultaneously, the male partner provides a semen sample, or if needed, sperm is surgically retrieved from the testes or epididymis. The collected sperm sample is then processed in the lab to isolate the healthiest and most motile sperm.
The actual ICSI fertilization takes place under a high-powered inverted microscope. An embryologist uses a specialized holding pipette to gently secure a mature egg. A single, healthy sperm is then selected, often immobilized by a gentle touch to its tail, and aspirated into a fine microinjection needle. The needle is carefully inserted through the egg’s outer layer and into its cytoplasm, where the single sperm is released.
After injection, the eggs are placed in an incubator and monitored for signs of fertilization, which typically occurs within 18 to 24 hours. The resulting embryos are then cultured in the laboratory for three to five days before the best-quality embryo or embryos are selected for transfer into the woman’s uterus.
Outcomes and Considerations
ICSI achieves a high fertilization rate, typically 50% to 80% of injected eggs. However, fertilization does not directly guarantee a successful pregnancy or live birth. The ultimate success rates for pregnancy and live birth with ICSI are comparable to those with conventional IVF once fertilization has occurred.
Success rates for ICSI are influenced by several factors, with maternal age a key factor; younger women have higher success rates due to better egg quality. For women under 35, the average live birth rate per IVF cycle with ICSI is approximately 30-35%. This rate can decline to around 35-40% for women aged 35-37, and further to 10-25% for women over 40. While ICSI can overcome severe male factor infertility by ensuring sperm and egg interaction, studies suggest that for couples without male infertility issues, ICSI may not significantly improve pregnancy or live birth rates compared to conventional IVF.