Male fertility may be more complex than previously imagined. The combination of motility and semen volume traditional measurements of semen quality are not, it seems, as important as other factors when predicting the likelihood of impregnation.
Results of a study of 430 couples show that while the possibility of conception increased with increasing sperm concentration up to 40 x 104 /mL seminal fluid, it was also very important that the sperm were of normal shape (morphology) and motility.
The study found that a man with a lower sperm concentration is still likely to be fertile, providing a high proportion of the sperm present were of a normal morphology.
The study also found that sperm concentrations above 40 x 104 /mL did not make a man significantly more likely to impregnate his partner. Indeed, some men with sperm counts above the lower limits of normal (20 X 104 /mL, as defined by the World Health Organisation, may actually be sub fertile (Lancet, 1998; 352: 1172-7).