For decades, researchers have attempted to use a centrifugation (spinning) method to separate X and Y sperm for gender selection purposes. Dr. Ronald J. Ericsson of Gametrics Limited developed this method in the early 1970’s. He first used a simple filtering process based on the scientific fact that the X chromosome is larger than the Y chromosome, therefore, he assumed X-bearing sperm were heavier than Y-bearing sperm and would consequently reach the bottom of a tube first.
In Ericsson’s patented method, semen is placed in a test tube on top of increasingly thicker layers of the protein albumin. Rapid spinning in a centrifugal machine causes particles in a liquid to separate into layers, based on their density. The heavier, denser X-sperm (female producers) were thought to separate from the lighter Y-sperm (male producers). Following Ericsson’s lead, researchers began reporting experiments of spinning sperm in various types of solutions, and several initially reported success in creating all X- or all Y-sperm samples. The best known is Ericsson’s albumin method, possibly the only sperm-spinning method still used today.
Once separated, couples desiring a male baby have their doctor inseminate the prospective mother with the X or Y sperm. Ericsson has claimed a 78% to 85% success rate for boys, 73% to 75% for girls.
The problem is that although the chromosomal DNA mass is 2.8% greater in female sperm, the mass of the entire sperm cell includes many other parts, like the tail, membranes and vesicles. The overall difference in the mass between male and female sperm is essentially miniscule and negligible. Most fertility experts dismiss this method as ineffective. Numerous medical studies using reliable methods have shown that the Ericsson method does not alter the 50:50 ratio of Y and X sperm as originally claimed.