Sperm: Embryologist Reveals the Difference Between 'Good' and 'Bad' Swimmers

When it comes to male fertility, not all sperm are created equal. In an Instagram reel, embryologist Dr. Lisa Lee (@drlisalee_ivf) broke down the differences between "good" and "bad" swimmers, analyzing semen samples and pointing out key characteristics. As an embryologist of over 15 years' experience, Dr. Lee works in an IVF lab, helping infertile couples create embryos in a controlled environment. She told Newsweek that while sperm motility is important, it's not the only factor in fertilization.

"A bad swimmer can still fertilize an egg and result in a healthy pregnancy, but it's the DNA inside that matters," Dr. Lee said. "[The] majority of the sperm shown in the video won't make it to the egg but in IVF, we can assist by injecting the sperm directly into the egg for fertilization." In the clip, which has amassed 3.2 million views, Dr. Lee first points out sperm with "bad necks" that struggle to swim straight. Next, she identifies a sperm with a mix of abnormalities and warns that agglutination—when sperm cells stick together—"is not good." She then showcases what healthy, motile sperm should look like before challenging viewers to "spot the pinhead sperm swimming downwards." Other poor examples include a sperm swimming in circles and another case where two sperm have their heads fused together. Dr. Lee explained that proper anatomy, such as the head shape, midpiece, tail formation and length, is key when it comes to good quality sperm. "However, just because it's a good swimmer doesn't mean it necessarily has the right amount of DNA, but being a good swimmer does mean it's more likely to be a normal sperm," she said. Dr. Lee's clip also clocked up over 53,000 likes and hundreds of comments. Many users were fascinated by what they could see under the microscope. "It's truly amazing how everything comes together for us to be born," one user wrote. "If I ever date, I'm bringing my guy to the lab first, to see if there's a future," a second joked. Other users pointed out that men also have a big part to play in their female partner's pregnancy. "The blame for pregnancy complications was and is still blamed on women. I hope that with time we'll get rid of the bias," another wrote. Dr. Lee also explained how lifestyle choices significantly impact sperm health. "A life cycle of sperm is typically between 72–74 days, [meaning], lifestyle factors will impact the formation of sperm in the testes," she said. For those looking to optimize sperm for conception, Dr. Lee advised minimizing or eliminating alcohol, not smoking or taking recreational drugs. "Diet will also have an impact. Don't forget it takes almost three months for the sperm life cycle, so start working on this early," she said. Do you have a tip on a health story that Newsweek should be covering? Do you have a question about fertility? Let us know via science@newsweek.com.