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Sperm Spinning for Gender Selection:
Sperm Swim-Up

The story behind sperm swim-up for gender selection is almost exactly the same as with the Percoll method: separation of X and Y-sperm is suspected as a side effect of a standard technique used to isolate motile sperm for use in artificial insemination. Couples being treated for infertility who do not want gender selection can be assured that this commonly used technique has been proven not to change the X:Y ratio of sperm.

Sperm Preparation by Sperm Swim-Up

  • Semen is placed in a test tube; in some cases, it is previously washed and centrifuged.
  • A culture medium is carefully placed on top of the semen. The medium is a hospitable environment for the sperm, and healthy sperm will swim up into it. Slow and immotile sperm are left behind, along with most debris in the semen.
  • The test tube is let stand an hour or so; in some cases it is placed at an angle, and/or in an incubator.
  • In the standard procedure, the top layer is collected for use. In the modified swim-up technique for attempted male gender selection, a small fraction of the top layer is first discarded. This practice is based on the theory that a) a small fraction of X-sperm are the fastest of all, b) next fastest are the Y-sperm, and c) slowest are the majority of X-sperm. The modified swim-up attempted to discard that first group of fast X-sperm.
  • Finally, the portion retained for use may be washed and centrifuged again.

Published Medical Studies About Sperm Swim-Up

A Controlled Study for Gender Selection Using Swim-Up Separation
1998, Gynecologic and Obstetric Investigation (New York)
  • The modified swim-up technique was used to achieve 52 pregnancies of 15 mothers wanting a girl and 37 wanting a boy.
  • For those wanting a girl, clomiphene citrate and human chorionic gonadotropin was administered. One IUI was performed on cycle days 12-14 when the follicle was 18-22mm, using the bottom layer of the separated semen.
  • For those wanting a boy, one IUI was performed when the follicle was 18-22mm, using the top layer of the separated semen.
  • The success rate was 87% for a girl, and 89% for a boy.
  • "This study reveals that the modified swim-up method with additional monitoring results in statistically significant gender preselection."
Failure of multitube sperm swim-up for sex preselection
Jun-1997, Fertility & Sterility (Nebraska)
  • A modified swim-up technique was used on semen samples from donors reporting for routine semen analysis.
  • X:Y ratio was verified by double-label fluorescence in situ hybridization (FISH), and was found to remain at 1:1 after swim-up.
  • "No clinically significant change in the ratio of X- to Y-bearing spermatozoa was detected independent of time. Therefore, clinical application of this procedure should be strongly discouraged."
Detection of X- and Y-bearing human spermatozoa after motile sperm isolation by swim-up
Dec-1993, Fertility & Sterility (Australia)
  • The swim-up technique was used to process semen samples from 10 healthy donors.
  • The X:Y ratio was verified by double-label fluorescence in situ hybridization (FISH).
  • The X:Y ratio was found to be essentially 1:1 both before and after swim-up.
  • "Because [swim-up] is an important procedure for routine IUI, IVF-ET, and GIFT, the results of this study are important reassurance that the sex ratio is not altered by this method of sperm preparation."
A prospective study to evaluate the efficacy of modified swim-up preparation for male sex selection
Feb-1993, Human Reproduction
  • The sex ratio of births following the use of a modified swim-up technique was 88.5% male, compared to 50% male/female using the Percoll method sperm.
  • "One must hypothesize that the modified swim-up procedure damages the x-spermatozoa."
The sex ratio of normal and manipulated human sperm
Feb-1993, Fertility & Sterility
  • Semen samples were analyzed after swim-up or Sephadex filtration.
  • The ratio of Y-sperm was determined using quantitative polymerase chain reaction (PCR), considered to be a much better method than quinacrine but less accurate than double-label FISH.
  • Before processing, the X:Y ratio was close to 1:1. Neither swim-up or Sephadex filtering altered the ratio.