When trying to conceive, it is understandable that couples want to optimize their chances by using the highest quality sperm. But what defines good sperm? Understanding what makes some sperm better than others can help inform decisions about conceiving naturally or steps to take before attempting pregnancy.
Sperm Morphology
One of the main factors in sperm quality is morphology – the size and shape of the sperm. Normal sperm have an oval-shaped head and a long tail. Abnormally shaped sperm may have defects in the head, midpiece or tail.
Sperm morphology is analyzed as part of a semen analysis. The World Health Organization standards state that in a normal semen sample, at least 4% of sperm should have normal morphology. Samples with less than 4% normal forms may indicate lower fertility.
There are several types of abnormal shapes that can occur:
- Large heads – The heads of sperm are larger than normal.
- Small heads – The heads of sperm are smaller than normal.
- Tapered heads – The heads come to a point instead of being oval.
- Round heads – The heads are round instead of oval-shaped.
- Amorphous heads – The heads have an irregular, undefined shape.
- Bent necks – The sperm neck is angled rather than straight.
- Bent tails – The tail is curved or crooked.
- Coiled tails – The tail is twisted into a corkscrew shape.
- Two heads – Some sperm have two heads instead of one.
- Two tails – Some sperm have two tails rather than one.
In general, sperm with normal oval-shaped heads and long straight tails have the best morphology. Abnormalities can impair the sperm’s ability to reach and penetrate the egg. For example, sperm with misshapen heads may not recognize the egg or release enzymes properly. Tails that are coiled or bent will not be able to propel the sperm forward correctly.
Sperm Motility
Another vital aspect of sperm quality is motility – the ability to move properly. Sperm motility is graded based on the speed and direction of movement:
- Progressive motility – Sperm move forward in a straight line at a moderate to rapid speed.
- Non-progressive motility – Sperm do not move forward despite motion; they may only jitter or swim in tiny circles.
- Immotile – Sperm do not move at all.
Sperm with progressive motility have the highest quality. At least 32% of sperm should show progressive motility in a normal semen sample. Lower percentages can indicate problems with sperm function.
Non-progressive and immotile sperm have difficulty reaching the egg. The vigor and propulsion of sperm movement are vital for penetrating cervical mucus and the egg shell. Weak swimming diminishes the chances of fertilization.
Sperm Concentration
Sperm concentration, also known as sperm count, is another parameter examined in semen analysis. It refers to the number of sperm per milliliter of semen. Normal values are:
- 15 million sperm per mL or greater
- Total sperm number of 39 million per sample or higher
Low sperm concentration, known as oligozoospermia, indicates some degree of infertility. Azoospermia refers to no sperm at all in the semen. Sperm counts under 15 million/mL are associated with reduced rates of conception.
However, having a higher sperm concentration does not necessarily equal better fertility. Sperm function and quality matter more than sheer numbers. An sample with 80 million sperm/mL is not necessarily twice as fertile as one with 40 million/mL if the sperm have poor morphology and motility.
Sperm DNA Fragmentation
Sperm DNA fragmentation is a measure of damaged DNA in the sperm. It can be tested with sperm chromatin structure assay (SCSA) or sperm chromatin dispersion (SCD). Normal values are less than 15% DNA fragmentation.
Higher levels of sperm DNA damage are associated with:
- Lower fertility
- Lower embryo quality
- Higher miscarriage rates
DNA damage can interfere with the sperm’s ability to fertilize the egg and activate the embryo’s genes after fertilization. Testing for DNA fragmentation provides additional information beyond standard semen analysis.
Sperm Selection Techniques
Various techniques exist to separate the highest quality sperm from a semen sample:
Density Gradient Centrifugation
This technique uses a centrifuge to separate sperm based on the difference in density between sperm and other cells/debris. Sperm are isolated on a density gradient solution. It selects motile, morphologically normal sperm.
Swim-Up Method
With this method, semen is layered under culture media in a tube. After incubation, the most motile sperm swim up into the media and are collected. Less robust sperm remain at the bottom of the tube.
Microfluidic Sperm Sorting
This emerging technology uses microfluidic chips to isolate sperm. Flow channels guide motile sperm based on fluid mechanics. It allows real-time sorting of thousands of sperm.
Magnetic-Activated Cell Sorting
MACS involves incubating sperm with magnetic beads coated with antibodies. Abnormal sperm bind to the beads, while healthy sperm remain in suspension. A magnet separates bead-bound and unbound sperm.
These techniques may be used in conjunction with IVF or intrauterine insemination to select the most optimal sperm. This can enhance pregnancy rates compared to using unprocessed sperm samples.
Sperm Selection in IVF
In IVF, embryos are examined to help select the ones most likely to implant. Similar principles are sometimes applied to sperm selection:
Intracytoplasmic Morphologically Selected Sperm Injection (IMSI)
IMSI is a variation of ICSI, in which sperm are examined at 6000x magnification. Abnormally-shaped sperm are discarded, and the best looking sperm are injected into each egg.
Blastocyst Biopsy with PGT-A
Embryos can be biopsied at the blastocyst stage and tested with preimplantation genetic testing for aneuploidy (PGT-A). Testing reveals which embryos are chromosomally normal. This indirectly provides information on which sperm created healthy embryos.
Time-Lapse Imaging
Incubators with time-lapse imaging track embryo development over time. The growth patterns and timing provide clues about the quality of the sperm that formed the embryo.
These strategies help identify sperm less likely to transmit defects causing embryo arrest or miscarriage.
Impact of Male Age and Lifestyle
A man’s age and lifestyle affect sperm quality:
Age
As men get older, sperm morphology, motility, and count tend to decline. DNA damage also increases with age. Paternal age over 40 is associated with higher miscarriage rates.
Smoking
Smoking can damage sperm DNA through oxidative stress. It is linked to reduced sperm count and motility.
Alcohol
Heavy alcohol use can lower testosterone, impair sperm production and function, and increase DNA fragmentation.
Obesity
Obesity is connected to lowered sperm count, motility, and abnormal morphology. It may impact hormones regulating sperm production.
Drugs
Certain drugs like anabolic steroids, marijuana, and chemotherapy agents can reduce sperm count and quality.
Radiation & Toxins
Environmental toxins and radiation sources can generate free radicals damaging to sperm DNA.
Optimizing the man’s health through diet, exercise, avoiding toxins, etc. can improve sperm quality before conception.
Key Takeaways
In summary, good quality sperm generally have these characteristics:
- Normal oval-shaped heads
- Long straight tails
- Good progressive motility
- Higher total sperm count
- Lower DNA fragmentation
High quality sperm have the greatest potential to result in a healthy pregnancy. Understanding sperm morphology, motility, count, and DNA integrity helps gauge fertility status. Techniques to select the most optimal sperm can maximize conception success.
Conclusion
The quality of sperm plays a major role in natural and assisted conception outcomes. While there is no single perfect measure of sperm health, examining multiple parameters provides a comprehensive picture. Couples trying to conceive should take steps to optimize the man’s fertility through lifestyle choices. Talk to a doctor if sperm quality issues are suspected after semen analysis. Techniques exist to isolate the healthiest sperm and give couples the best chances of pregnancy.