No fertilisation; no embryo development; no implantation

Fertilisation can fail, and fertilised eggs can fail to divide or undergo cleavage properly. The reason can lie with the sperm (usually fertilisation failure rather than cleavage failure), with the egg, or both.

Fertilisation can fail when not enough sperm attach to the egg’s surrounding coat. This can happen because the number of healthy sperm is too low, or because there are antisperm antibodies that prevent sperm from attaching. Either way, future cycles can overcome this problem by using intracytoplasmic sperm injection (ICSI).

In addition, fertilisation and/or cleavage might fail if the follicles from which the eggs were extracted had begun to fail prior to egg collection. This can be an inherent problem with the ovaries or it can result from suboptimal stimulation.

Most embryos that fail to implant and/or fail to result in a baby (even though they might look normal in the lab) fail through a combination of intrinsic and extrinsic shortcomings. Intrinsic shortcomings might be based on insufficient metabolic energy or an abnormal chromosome count. Extrinsic shortcomings might occur during follicular stimulation or in very rare cases, during laboratory handling.

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