Sperm Morphology
The shape and structure of sperm cells; at least 4% normal forms (Kruger criteria) is considered adequate.
Morphology assesses whether sperm are shaped normally — oval head, intact midpiece, and single uncoiled tail without excess cytoplasmic droplets. The WHO uses the strict Kruger criteria, which classifies a sperm as normal only if it meets very precise dimensional standards. A result above 4% normal forms is considered normal.
Teratozoospermia (low morphology) is associated with reduced fertilization rates in conventional IVF and may prompt a recommendation for ICSI, where a single sperm is injected directly into the egg.
Morphology can be temporarily reduced by fever, infection, heat exposure, and certain medications. Lifestyle improvements may modestly improve morphology over several months.
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