A new study from Spain may offer a way to improve the success rate of in vitro fertilization (IVF) procedures with no additional cost or hormone interventions. Improved outcomes are anticipated by using only the most promising portion of a man’s ejaculate to fertilize an egg. The study finds that the most virile sperm are ejaculated first and the remainder of the ejaculated fluids may actually hinder fertilization.

“Ejaculate has always been considered as a whole,” according to María Hebles, who led the study from the Ginemed Assisted Human Reproduction Clinic in Seville. In a typical IVF procedure, it is collected in one container, mixing the earliest ejaculated fluids with those that come later. “This could have a detrimental effect on the sperm population,” according to Hebles.

To test her theory that not all semen is created equal, she and her research team enlisted 40 men to provide two semen samples from one ejaculation, with the first ejaculate going into one container and the remainder in a second container. The researchers discovered:

  • The first ejaculate fraction (FEF) contained secretions from the prostate gland.
  • The second ejaculate fraction (SEF) contained more secretions from the seminal vesicle.
  • The FEF accounted for approximately 15% to 45% of total ejaculate volume while the majority was produced by the SEF.
  • The FEF contained fewer individual sperm cells but these were of much higher quality than those which came later. The FEF sperm were greater in number, more highly concentrated, more vigorous, and contained healthier DNA than those of the SEF.
  • The FEF also contained higher concentrations of zinc, magnesium, citric acid, and acid phosphatase which promote the health of the sperm while protecting it from the acidic environment of the vagina.
  • The SEF fluids contained a higher concentration of elements known to damage sperm health.

Hebles speculates the initial release of the most viable sperm enhances the chance of fertilization while the less fertile secondary ejaculate uses its damaging elements to ensure no rival sperm from another source impregnates the egg. The current protocol of mixing all ejaculated fluids into one container may actually hinder fertilization in some cases. She suggests asking men to collect their ejaculate in two fractions to improve the likelihood IVF will result in fertilization.


  1. Hebles, María, et al. "Seminal quality in the first fraction of ejaculate." Systems Biology in Reproductive Medicine 61.2: 113-16. Informa Plc. Web. 15 June 2015.
  2. "Semen: What is Semen." SexInfo Online. University of California, Santa Barbara, 2015. Web. 15 June 2015.