Normal Male Fertility and Pregnancy Rates
An Overview of Normal Male Fertility
Normal Pregnancy Rates
When couples with no known infertility issues start trying to have a baby, their odds of achieving a pregnancy are about 15–25 percent each month. About 75-80 percent of these couples will have successfully established a pregnancy within six months, and 90 percent will have done so within one year. After a year of unsuccessful trying, however, a couple’s chances of naturally establishing a pregnancy will have dropped to approximately 3–5 percent each month.
Normal Sperm Production
Sperm production is initiated and maintained by the male hormonal system. The pituitary gland, which sits at the base of the brain, is the hormonal “control center” of the body. Cells within the front part of the pituitary gland produce two very important hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH induces the spermatogenic cells within the testicles to make sperm, while LH signals the Leydig cells within the testicles to make testosterone.
FSH and LH play complementary roles in normal sperm production. Without FSH, the spermatogenic cells would not make sperm. However, sperm production requires high testosterone levels within the testicles; hence the importance of LH stimulation to drive increased testosterone production.
Normal Sperm Maturation
Unlike women, who are born with all the eggs they will ever have, after puberty men continuously make new sperm. The sperm development process takes approximately ten weeks, as sperm precursor cells slowly transform into fully mature sperm. During this maturation process, the sperm leave the testicle and enter into the epididymis, a structure that wraps around the side of the testicle. When sperm leave the epididymis and enter into the long tube called the vas deferens, they are fully mature and ready to swim. Large numbers of sperm are concentrated within the vas deferens in preparation for future ejaculation.
Normal Male Sexual Function
The bulbourethral glands (also called Cowper’s glands) are a pair of small glands that sit beneath the urethra near the prostate. During sexual intercourse, the bulbourethral glands produce a small amount of clear fluid (called pre-ejaculate) that lubricates the urethra and neutralizes the acidity of any residual urine left behind from the last urination. When ejaculation occurs, the vas deferens rhythmically contracts, forcing the sperm to flow into the ejaculatory ducts. Within the ejaculatory ducts, the sperm pick up fluid from the seminal vesicles, which then joins fluid from the prostate gland as it enters the urethra. Strong contractions of the surrounding muscles then force the sperm out of the urethra, through the tip of the penis, and into the woman’s vagina.
Following ejaculation, sperm are deposited near the woman’s cervix, which is a structure at the top of the vagina leading into the uterus. The part of the ejaculate fluid that was produced by the seminal vesicles causes the semen to coagulate (stick together), and this helps to protect the sperm from the harsh, acidic environment of the vagina. The prostate fluid contains enzymes that gradually release the sperm from the coagulated mass of the rest of the ejaculated fluid, thereby allowing the sperm to enter the woman’s cervix. Hormonal changes in women around the time of ovulation (when a mature egg is released from the ovary) cause the cervix to be more receptive to allowing sperm to pass into the uterus. The sperm then swim up the uterus into the fallopian tubes in search of an egg. During this process, the vast majority of the sperm will die. Only a small number of the fittest, best-swimming sperm actually make it up the fallopian tubes to the area where fertilization can occur. If the timing is right, these sperm will meet up with an egg that has been released from the woman’s ovary. A single sperm will penetrate the egg, causing a chemical reaction within the egg that excludes any other sperm from entering as well. The miracle of fertilization and embryo development then ensues, with the embryo traveling down the rest of the fallopian tube and implanting within the wall of the uterus, the lining of which has thickened under hormonal influence to grow and provide the rich blood supply necessary to sustain a growing embryo.
Conception is a fascinating and complex process. Although it takes place within the female reproductive tract, the male contribution obviously plays a vital role and contributes half of the DNA of the future baby. With all of the myriad steps and mechanisms necessary for normal conception, it is amazing that the process proceeds normally in the majority of couples. There are many steps along the way, though, where problems can present themselves, and overcoming these obstacles to fertility on the male side is the focus of this book.