Sperm may seem an odd choice of subject for a “young woman’s guide to gynecology and obstetrics.” But it is this last word, obstetrics, that makes sperm a good choice for an entry subject. Arguably, without sperm, obstetrics would not exist. This may not always be the case, but for the time being, each human pregnancy makes use of sperm somewhere in the process. So, let’s talk about sperm, baby!
Sperm is the male counterpart to the female gamete, the ovum (or egg). Technically, what we commonly refer to as a sperm should be considered more of a sperm cell called a spermatozoon (spermatozoa, plural). Since virtually everyone refers to the spermatozoon as a sperm, I will continue to use the word sperm in its place. The human sperm consists of, ostensibly, a head an a tail. This simple-looking structure belies its key importance in creating life. Stored within the sperm is a complex DNA code that will (usually) determine the sex of the resultant child and influence its phenotypical appearance–short or tall, dark or light, thin or stout–and many other genetic factors.
Each sperm is about three micrometers at its widest and about fifty micrometers long. The tail of the sperm powers it forward, almost like a propeller, at about 1 to 3 millimeters per minute. The semen, the fluid in which sperm are expelled from the male, has a chemical balance that keeps the sperm mostly inert until it is neutralized by the acidic environment of a vagina. The sperm, when entering the vagina, journey upward in search of an egg to fertilize. If the sperm do find an egg they will attempt to penetrate the membrane. A single sperm will succeed in penetrating the egg and the fusion of the two begins the process of meiosis in which the DNA of the mother and the father are spliced together to form a new set of DNA.
At this point, the sperm has reached its goal and blends into the developing human. However, the sperm has many variations and not all sperm conform to the usual model we have in mind. Abnormal sperm are actually quite common and come in many varieties. For example, there are sperm with two heads, two tails, both, neither, and various other extra and missing parts. Most abnormally structured sperm do not pose a genetic complication or threat to a potential pregnancy. Because of structural deficiencies these abnormal sperm are not likely to reach an egg in the first place.
In all, sperm are an interesting and integral part to creating life and without them, there would be little basis for obstetrics. So, any time you are thinking about obstetrics keep in mind the “little swimmers” that help make it possible. Comments, questions, otherwise? Please bring them forward!
 I am careful to say that the sperm usually determines the sex of a child because certain genetic problems can preclude a child with XY sex chromosomes from developing male characteristics, including genitalia, thus the Y-sperm from the father in this case does not determine the sex of the child.