Sperm processing affected ratio of X- and Y-bearing sperm

Studies showed that assisted reproductive technology changed the sex ratio at birth, but the effect of semen processing (swim-up technique and density-gradient separation) on enriching either Xor Y-bearing sperm is always controversial. We recruited 30 healthy males and their semen samples were obtained by masturbation after sexual abstinence for 2-7 days. Each sample was divided into 3 aliquots: 1 as control without sperm processing, and the other 2 were handled with density-gradient or swim-up separation. Fluorescent in situ hybridization (FISH) was used to verify the ratio of Xand Y-bearing sperm. We found X/Y sperm ratio was significantly different among the 3 groups, with gradient group vs control group (1.04±0.04 vs 1.0±0.03, P<0.001), swim-up group vs control group (0.48±0.04 vs 1.0±0.03, P<0.001), and gradient group vs swim-up group (P<0.001). We concluded that swim-up technique enriched Y-bearing sperm and density-gradient separation enriched Xbearing sperm, though X/Y sperm ratio before fertilization is not necessarily parallel with human sex ratio at birth.