In a popular fertility treatment that helps infertile men become fathers, a single sperm is injected into an egg to induce fertilization.  As a rule, embryologists select the sperm that looks the best under the assumption that the best-looking sperm is also the healthiest.  Researchers at the Jones Institute for Reproductive Medicine in Norfolk, Virginia, however, have determined that microscopic inspection of even the best-looking sperm can harbor DNA that is damaged enough to jeopardize a pregnancy or the health of a child born under such circumstances.

The fertility treatment, intracytoplasmic sperm injection (ICSI), is used when men are infertile due to moderate or severe abnormalities of the sperm, a condition known as teratozoospermia.  In such cases, the sperm’s abnormalities are visible under microscopic examination.  Visibly damaged sperm are rejected for this procedure while the single sperm in a sample that looks the best is used.  Sperm health is determined by the regular, oval shape of the head and its long, straight tail.

Conrado Avendano and his colleagues from the Virginia institute took the examination one step further and found that looks can be deceiving.  Using sperm samples from both fertile and infertile men, the team randomly selected 400 individual sperm cells from each sample.  They evaluated each sperm using standard measures but also examined each sperm cell using fluorescence microscopy, which reveals the integrity of the DNA in each cell.

The research team found that even cells that look acceptable under the standard microscopic examination were likely to have fragmented DNA under fluorescent examination.  The DNA damage, or fragmentation, makes successful fertilization problematic.  DNA damage was found in 20% to 66% of the sperm cells that appeared visually normal.

DNA damage in the sperm reduces the chance of pregnancy and can lead to miscarriage when a pregnancy does occur.  In the event a child is born of such a pregnancy, the child’s risk of chromosomal abnormalities are increased, as are birth defects and childhood cancer.

Several factors are known to cause DNA fragmentation, including a man’s age, smoking habits, abnormal testicular warming, and exposure to air pollution.  Infections of the reproductive tract can cause oxidative stress that also damages sperm DNA.

Avendano believes sperm selection should include examination of the DNA to ensure the best results and healthiest children instead of a mere visual check when ICSI is being undertaken.  He would like to see more research into the biology of the sperm to minimize future problems.  He presented the findings of his study at the European Society of Human Reproduction and Embryology’s 24th annual conference on July 8.

Source: European Society for Human Reproduction and Embryology