Human reproduction is often considered a “miracle” due to the relative difficulty of successfully getting pregnant – even under ideal conditions, successful fertilization is not guaranteed. Now, a new study from the assisted human reproduction clinic Ginemed in Seville, Spain sheds some light on why that is: Ejaculate from males actually comes in two parts, with the second part actually being detrimental to the sperm’s survival.
“The ejaculate has always been considered as a whole. However, we think that is divided into two well differentiated by their composition and physiological functions, aimed at getting two equal shares in major reproductive phases,” explains Maria Hebles, co-director of the laboratory of reproduction clinic Ginemed Seville (Spain) and first author of the study.
The seemingly strange dichotomy is the result of a quirk of human evolution: The first expulsion of ejaculate contains the strongest, healthiest sperm which set out with the intention to fertilize the female egg. Subsequent bursts, however, have a different objective. They contain compounds designed to inhibit sperm, with the thought being that it’s the male body’s way of preventing any future suitors from successfully fertilizing the egg themselves.
The problem for couples, particularly those struggling to conceive, is that the ejaculate phases are difficult (if not impossible) to separate in a normal sexual setting. In order to test the hypothesis, researchers worked with 40 participants to collect ejaculate in two containers – one for the first expulsion, and one for everything else. Scientists were then able to study the two phases independently of one another.
The researchers found that the first bursts of ejaculate account for anywhere from 15-45% of the total volume, and tend to be richer in sperm count and health. They also contain acid phosphatase, citric acid, magnesium and zinc, which the researchers say have help insulate the sperm from damaging compounds. The later bursts, on the other hand, contain reactive oxygen elements which can actually damage sperm.
“As expected, the sperm of the first phase of the ejaculate were higher in mobility and counting and, more importantly, had a higher integrity of sperm DNA from the second phase,” said Hebles.
For couples looking to in vitro or other assisted fertilization techniques, the finding is a godsend: A novel, non-surgical way to significantly improve their odds of conception at virtually no cost.