Poor Embryonic Morphology Due to Sperm

Semen tests that indicate the presence of abnormal sperm are not uncommon and not necessarily bad, according to Dr. Todd Nippoldt of the Mayo Clinic. Although sperm morphology does affect male fertility to some degree, it is unlikely that misshapen sperm will have any affect on embryos. This is due largely to gamete (sperm cell) competition, which ensures that only the healthiest sperm are able to fertilize egg cells.

Healthy Fertilization

• Normal sperm primarily consist of two parts: an ovular head and a whiplike tail. The motion of this tail is what allows the sperm to swim through the passages of the female reproductive system and possibly fertilize an egg. The egg and sperm fuse upon fertilization and form a single-celled zygote, which will divide several times to form a multicellular embryo. At the embryonic stage, the cells of the major bodily systems begin to differentiate; hence, proper embryonic morphology is crucial to development.

Sperm Competition

• Upon human male ejaculation, an average of 280 million sperm are released from his body. Of these 280 million, only one (or, in the case of some twins, two) will finally fuse with a female egg cell to form a zygote, the precursor to an embryo. In other words, 280 million sperms cells must compete to penetrate the egg cell. In addition, the sperm must subsist in the harsh environment of the female reproductive system before any cell is able to fertilize an egg.

Fertilization

• Due to the enormous amount of competition between sperm cells, unhealthy sperm have a reduced chance of successfully fertilizing egg cells. Common sperm abnormalities include sperm with two heads, multiple tails, or other motility issues. The normal sperm cells will have a speed advantage over the abnormal cells, and will therefore be more likely to fertilize the eggs to form zygotes. Slow or immobile sperm will be also be more exposed to the acidic conditions in the early portion of the female canal, which will eventually kill the sperm.

Embryo Morphology

• If by chance an abnormal sperm did fuse with an egg cell and grow into an embryo, Dr. Nippoldt says there is no increased chance of abnormal embryo morphology or future birth defects. Abnormal embryos are usually the result of a chromosomal defects, which are equally likely to occur in the sperm or the egg. Benkhalifa and Menezo confirm that chromosomal abberations are the most significant cause of poor embryonic morphology.

Embryonic Development

• If an embryo were to develop severe morphological problems due to chromosomal defects (from either the sperm or the egg), the embryo would cease to develop due to insufficient genetic information or widespread cellular death as a result of the chromosomal aberration. As stated in Healthy Fertilization, morphology is crucial to development. Defective embryos could not progress into a viable human being, and the body would take appropriate action to cease further growth. Birth defects are a result of trauma later in the pregnancy or minor chromosomal changes, not from abnormalities in early-stage embryonic morphology.