Sperm morphology — the size and shape of sperm — is one factor that's examined as part of a semen analysis to evaluate male infertility. Sperm morphology results are reported as the percentage of sperm that appear normal when semen is viewed under a microscope.

Normal sperm have an oval head with a long tail. Abnormal sperm have head or tail defects — such as a large or misshapen head or a crooked or double tail. These defects might affect the ability of the sperm to reach and penetrate an egg. However, having a large percentage of misshapen sperm isn't uncommon. Typically, only around 4% to 10% of the sperm in a semen sample are normal, meaning that the vast majority don't look perfect under the microscope.

Sperm morphology is poorly understood, and it can be subjective. Scores can vary on the same semen sample, in the same lab, using the same scoring techniques. Most male fertility experts agree that the role of sperm morphology in predicting pregnancy is unclear, and that it's a poor predictor of infertility unless nearly 100% of the sperm are abnormal.

Along with sperm morphology, a typical semen analysis also assesses:

• Semen volume
• Total sperm number
• Sperm concentration
• Vitality (percent alive)
• Movement (motility)

An abnormal semen analysis doesn't mean that you are infertile. Many men with low semen analysis values can still father children — it just might take longer. If you and your partner aren't able to conceive through sexual intercourse, assisted reproductive technology such as in vitro fertilization might be an option.