It is well known that a woman’s age is a key factor in determining pregnancy outcomes. As a woman ages, the rates of miscarriage and congenital fetal malformations increase, while pregnancy and live birth rates decline; the risk of complications for older mothers significantly increases.
In contrast, the role of “sperm” appears to be diminished, with comments like “a man can make a woman pregnant at 90 years old” being common. The reasons for the poor development of embryos during the IVF process are varied. In the past, issues with embryos were always attributed to the eggs, but modern research has found that sperm quality also directly or indirectly impacts embryo development.
What indicators of sperm quality affect embryo development?
Currently, the main indicators used to evaluate sperm quality include sperm concentration, motility, morphology, and sperm DNA fragmentation index (DFI), among others.
1. Conventional indicators of sperm
Most studies believe that sperm concentration, motility, and total motile sperm count (TMC) do not have a significant relationship with the quality of embryos in ICSI cycles; however, a very low normal morphology rate may negatively impact embryo development.
In a foreign study involving 666 patients, researchers observed 1456 ICSI cycles and found that total motile sperm count had no significant effect on the development of embryos during cleavage stages. Conversely, domestic scholars conducting a retrospective analysis of 4756 IVF/ICSI cycles categorized sperm morphology into three groups: >15%, 4%-15%, and <4%, and found that, regardless of whether it was IVF or ICSI, the rate of high-quality embryos in the <4% group significantly decreased (P<0.05).
2. Sperm DFI fragmentation rate
Some studies suggest that sperm DFI affects embryo quality in IVF/ICSI cycles, while other studies indicate there is no significant correlation between early embryo development in IVF/ICSI and sperm DFI. Currently, the correlation between IVF/ICSI embryo quality and sperm DNA damage indicators is not universally recognized, although half of the published studies suggest that sperm DNA damage affects embryo quality, most of which are retrospective.
3. Morphology of sperm heads
The presence of vacuoles in sperm heads is one potential indicator. The IMSI system can magnify sperm by 6500 times to select sperm without vacuoles for ICSI injection, leading to an increased blastocyst formation rate. However, there is currently insufficient evidence from evidence-based medicine to demonstrate that IMSI can improve live birth rates and rates of miscarriage, necessitating further research.
4. Genetic and epigenetic factors of sperm affecting embryo development
(1) Since embryo gene expression begins during the embryo’s second division (4-cell to 8-cell stage), early research suggested that sperm nuclei did not have DNA transcription products (RNA), leading to the belief that only the egg’s transcription products were functional, irrelevant to sperm (which displeases sperm!). Recent research over the past decade has challenged or overturned this traditional view, revealing that sperm nuclei contain transcription products including not only mRNA, tRNA, and rRNA but also a large number of small RNAs, such as miRNA, siRNA, and piRNA. These small RNAs are carried into the egg upon fertilization by the sperm.
Research from domestic scholars found a significant correlation between sperm miRNA-34C levels and embryo quality after ICSI, with patients having higher quality embryos showing higher levels of sperm miRNA-34C than those with lower quality embryos. This suggests that sperm miRNA-34C could potentially serve as a predictor of embryo development in the future. Additionally, other scholars have reported that sperm DNA methylation patterns also affect embryo development. These molecular biology studies are progressing rapidly, with more sperm regulatory genes gradually being discovered, ultimately piecing together a complete mechanism map to explain the mysteries of embryo development.
(2) The balanced translocation of small segments at the ends of male chromosomes often quietly causes small deletions and duplications in embryonic chromosomes, leading to infertility, poor embryo development, and recurrent miscarriages. Conventional prenatal chromosome G-banding karyotype analysis often fails to detect these hidden “killers.” Without embryonic materials as clues, such as infertility, poor embryo development, or recurrent implantation failure, physicians are often “at a loss,” sometimes having to rely on more advanced testing and analysis methods to uncover the “culprit.”
[Summary 1] Egg quality is a key factor in embryo development, while sperm also influences embryo quality. Current research confirms that a high rate of sperm abnormalities may have a certain impact on embryo development. Additionally, sperm miR
