It is the shape and size of sperm. Which means the head of sperm should be oval in shape, have a mid-section, and have a long, straight tail. If sperm is a combination of double tail, no tail, or a head that has double heads, or too large, it is considered as abnormal sperm, and therefore unable to successfully enter into an egg. Most men have a large percentage of abnormal sperm, with only 4-15% of their sperm being considered normal.
Men with abnormal sperm can still be a parent; it may take longer time than normal to do so. If natural conception failed to work, you always have a second of assisted reproductive technology like in Artificial Insemination and Intra Cytoplasmic Sperm Injection (ICSI).
The following treatments can help you with the issues related to abnormal sperm
Intra-cytoplasmic sperm injection (ICSI)