Sperm Morphology - Kruger Sperm Function Test

    Q: What is the importance of morphology in a semen analysis?


    A: One important parameter in the semen analysis is the morphology, or shape of the sperm. The shape of the sperm is a reflection of proper sperm development in the testicle, or spermatogenesis. Men with a defect in sperm maturation tend to have problems with sperm morphology and may then be at risk for failure of their sperm to fertilize their partner's eggs.

    There are two methods for performing a semen analysis:

    1. Most clinical laboratories perform a crude estimation of the percentage of sperm in the ejaculated specimen that appear to have normal shape.
    2. Only specialized andrology laboratories have trained technicians that can perform a "strict" semen analysis. Only these "strict criteria" (also known as Krueger criteria) have been studied with regard to fertilization success or failure.

    If a man has a decreased number of normally shaped sperm on the Krueger strict morphology analysis, he is at risk of fertilization failure or at least low rates of fertilization. However, an increased number of abnormally shaped sperm with 'non-strict' criteria may indicate a fertilization problem, but to be certain this test should probably be repeated in a laboratory that performs strict analysis. Strict morphology is a useful test to perform with couples that have unexplained infertility, even if the semen analysis and non-strict morphology are otherwise normal.

    The strict morphology of the sperm predicts a man's fertility potential (fertilizing capacity) even in cases where the sperm count, motility and/or regular morphology of the SA are normal. The strict morphology takes a critical look at many individual sperm according to a very strict set of criteria. Only specialized andrology laboratories have trained technicians who can analyze the sperm according to these "strict criteria". The sperm are stained and examined under oil at 1000X power for normal size and shape of the head, mid piece, tail or for any other abnormalities. Even a minor defect in any category rates the sperm as abnormal. Therefore, relatively few sperm are rated as "normal" or perfect (near-perfect) during the strict morphology test, as compared to the "estimated crude morphology" done during a regular semen analysis (WHO criteria). The strict morphology score is a result that indicates and predicts the sperm's potential for fertilization:

    • Strict morphology score over 14 % normal: (normal; fertilizing capacity excellent)
    • Strict morphology score 4-14 % normal: (abnormal; possibly decreased or impaired fertilizing capacity)
    • Strict morphology score 0-3% normal: (abnormal; severe impairment or probable inability to fertilize