“Tinder for Sperm: Even in the Petri Dish, Looks and Athleticism Are Prized: What Makes One Sperm Cell—A Blob of DNA With a Tail—Stand Out? The Selection Process Is like a Microscopic Mr. America Contest”, 2019-07-18 (; backlinks; similar):
Fertility treatments have gone so high-tech, it’s logical to assume there’s an exact formula for each procedure. Embryos are frozen and warmed at precise temperatures, hormones are measured to the billionth of a gram, and women inject themselves with strictly-calibrated doses of drugs. But sperm selection remains more art than science. Though fertility specialists generally agree that an “ideal” human sperm has a smooth, olive-shaped head and a long, undulating tail, the degree to which the appearance of sperm cells correlates with their fertilizing potential is a subject of much controversy. It isn’t always possible to find sperm with this ideal physique in a given sample, Lo noted, and even homely, misshapen sperm can produce healthy babies. Sometimes, Lo said, “You pick the least ugly of the sample you have.”
…These days, many leading fertility centers use techniques that allow them to bypass all these steps. Instead, they pick a single sperm and inject it into the egg, a technique called intracytoplasmic sperm injection or ICSI (pronounced ICK-see). ICSI was designed to help men with few or defective sperm, but has become so common that it’s used in more than half of all I.V.F. procedures. (Despite its widespread use, studies have not proven that ICSI boosts pregnancy rates when men have sufficient numbers of healthy sperm.)
…Techniques to sort sperm by putting them through fine mesh filters and by having them swim through specially-engineered pathways called microchannels have also failed to yield better results than simply choosing by appearance. Research efforts continue but, for now, sperm selection is generally left up to the esthetic judgement of the individual embryologist.
…Since it’s impossible to individually examine each of the thousands of sperm in a typical sample, embryologists acknowledge that the quest for the best possible sperm involves an element of fate. “If I look in my scope and say, ‘That one looks really great’, I’ll choose it”, Lo explained. But if an especially strong swimmer darts across his field of vision, he sometimes changes course at the last minute. When this happens, he said, he wonders, “Did I choose that sperm? Did the sperm choose me?”