When a Semen Analysis is ordered, sperm morphology is an important parameter to consider. Sperm morphology specifically refers to the shape of the sperm, ideally with a single oval shaped head, neck or midpiece and a single tail. In order for morphology to be assessed accurately, the slide needs to be stained properly and observed under oil immersion since spermatozoa can often be mistaken for leukocytes, debris and round cells. Abnormalities of the head of the sperm may impair fertilization through failure of the acrosome reaction while tail defects are thought to decrease sperm Motility. The presence of a high number of tapered heads may be indicative of a varicocele.
For many years, the World Health Organization (WHO) criteria for normal sperm morphology was 30% while Kruger’s or strict criteria is 14%. Originally described by T.F. Kruger, M.D. in 1986, his studies have demonstrated a correlation between low sperm morphology and fertilization in IVF (in vitro fertilization) cycles. Men with low sperm morphology have lower fertilization rates than men with normal sperm morphology, but they can still achieve a pregnancy, particularly through IVF with intracytoplasmic sperm injection (ICSI). This year, the 5th Edition of the WHO was published, and the lower reference limit for sperm morphology by strict criteria is 4%. At Fertility Centers of Illinois, we continue to use the strict criteria for sperm morphology with 14% or above as the normal range.
The clinical question has been raised of a possible association between fertilization with abnormal shaped sperm and birth defects. There is a report by McKenzie et al. from 2004 of 45 men, all with no morphologically normal sperm by strict criteria, who underwent IVF with ICSI. Their offspring were followed to one year after birth with no congenital anomalies noted. A more recent article published this year by French et al. in over 1000 cycles performed with ICSI verified high fertilization, pregnancy and live birth rates with low miscarriage rates even in the group of patients with no morphologically normal sperm by strict criteria.
World Health Organization. WHO Laboratory Manual for examination and processing of human semen. Fifth edition, July 2010; Geneva: WHO Press.
French DB, Sabanegh ES, Goldfarb J, Desai N. Does severe teratospermia affect blastocyst formation, live birth rate, and other clinical outcome parameters in ICSI cycles? Fertility and Sterility 2010; 93: 1097-1103.