Fathers of non-identical twins have better quality sperm than other men, according to a study by Danish fertility specialists. The observation suggests that twinning rates could provide a useful measure of male fertility in a given population.
Earlier research had revealed that men who took longer to father a child were less likely to have non-identical (dizygotic) twins. And some research had hinted that non-identical twins were less common in populations with low male fertility. But there was little or no research on semen quality in fathers of twins, until now
A team at the University Hospital of Copenhagen compared sperm quality in
37 men who had fathered non-identical twins with a control group of 349 men with normal, healthy sperm. On average, they found that fathers of twins had more normal and motile, or mobile, sperm than the control group. Their sperm counts were also higher, although not significantly.
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“Our results support the idea that changes in semen quality may influence the non-identical twinning rates,” says team leader Camilla Asklund. Indeed, the researchers conclude that the prevalence of non-identical twinning in a population could prove a useful measure of male fertility.
Genetic differences
However, Lynn Fraser, a sperm expert at Kings College London, UK, suggests that genetic differences between different populations may be at least as important in determining the prevalence of non-identical twins.
“We know that in the Yoruba tribe in Nigeria, for instance, the rate of dizygotic twinning is 5.2%, which is very high, and this must be down to genetic differences that mean the women there are more likely to shed two eggs at once,” Fraser says. “And let’s not forget, if the woman doesn’t release two eggs, it’s not possible to have dizygotic twins in the first place.”
The Danish researchers concede that the chances of having non-identical twins is generally higher in older women, as the probability of releasing two eggs in one cycle rises with maternal age. Historically, about one birth in 80 gives rise to twins (1.3%). This rate has increased in some Western countries – particularly the US – in recent years due to the rise in IVF treatments.
However, if maternal factors are considered equal among fathers of twins and fathers of singletons, differences in the fertilisation of the two eggs released are probably related to semen quality, they say.
As part of the study, the researchers also tested the sperm quality of 15 men who had fathered identical (monozygotic) twins. Unexpectedly, they found that these men also had higher than average sperm quality. They were unable to explain this observation and say the finding might be an anomaly that occurred to due to the small sample size.
Journal reference: Human Reproduction (vol 22, p 751)
![Astronomers have long known that understanding how star clusters come to be is key to unlocking other secrets of galactic evolution. Stars form in clusters, created when clouds of gas collapse under gravity. As more and more stars are born in a collapsing cloud, strong stellar winds, harsh ultraviolet radiation and the supernova explosions of massive stars eventually disperse the cloud, and their light can bear down on other star-forming regions in the galaxy. This process is called stellar feedback, and it means that most of the gas in a galaxy never gets used for star formation. Researching how star clusters develop can answer questions about star formation at a galactic scale. Now, the state of the art has been further developed with both Hubble and Webb working together to provide a broad-spectrum view of thousands of young star clusters. An international team of astronomers has pored over images of four nearby galaxies from the FEAST observing programme (#1783), trying to solve this mystery. Their results show that it is the most massive star clusters that clear away their gaseous shroud the fastest, and begin lighting their galaxy the earliest. The team identified nearly 9000 star clusters in the four galaxies in different evolutionary stages: young clusters just starting to emerge from their natal clouds of gas, clusters that had partially dispersed the gas (both from Webb images), and fully unobstructed clusters visible in optical light (found in Hubble images). With Webb???s ability to peer inside the gas clouds, they were able to then estimate the mass and age of each cluster from its light spectrum. This image shows a section of one of the spiral arms of Messier 51 (M51), one of the four galaxies studied in this work, as seen by Webb???s Near-Infrared Camera (NIRCam). The thick clumps of star-forming gas are shown here in red and orange, representing infrared light emitted by ionised gas, dust grains, and complex molecules such as polycyclic aromatic hydrocarbons (PAHs). Within these gas complexes, each tens or hundreds of light years across, Webb reveals the dense, extremely bright clusters of massive stars that have just recently formed. The countless stars strewn across the arm of the galaxy, many of which would be invisible to our eyes behind layers of dust, are also laid bare in infrared light. [Image description: A large, long portion of one of the spiral arms in galaxy M51. Red-orange, clumpy filaments of gas and dust that stretch in a chain from left to right comprise the arm. Shining cyan bubbles light up parts of the gas clouds from within, and gaps expose bright star clusters in these bubbles as glowing white dots. The whole image is dotted with small stars. A faint blue glow around the arm colours the otherwise dark background.]](https://images.newscientist.com/wp-content/uploads/2026/05/13114322/SEI_296271016.jpg)
